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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2010	Jan. 31, 2011	Jun. 30, 2010
Document and Entity Information [Abstract]
Entity Registrant Name	BIOGEN IDEC INC.
Entity Central Index Key	0000875045
Document Type	10-K
Document Period End Date	Dec. 31, 2010
Amendment Flag	false
Document Fiscal Year Focus	2010
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 11,688,813,825.2
Entity Common Stock, Shares Outstanding		240,911,883

Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Revenues:
Product	$ 3,470,056	$ 3,152,941	$ 2,839,651
Unconsolidated joint business	1,077,244	1,094,863	1,128,238
Other	169,123	129,544	129,618
Total revenues	4,716,423	4,377,348	4,097,507
Costs and expenses:
Cost of sales, excluding amortization of acquired intangible assets	400,262	382,104	401,989
Research and development	1,248,604	1,283,068	1,072,058
Selling, general and administrative	1,031,540	911,034	925,305
Collaboration profit sharing	258,071	215,904	136,041
Amortization of acquired intangible assets	208,928	289,811	332,745
Restructuring charge	75,153
Acquired in process research and development	244,976		25,000
Gain on dispositions, net	1,643		(9,242)
Total cost and expenses	3,467,534	3,081,921	2,883,896
Income from operations	1,248,889	1,295,427	1,213,611
Other income (expense), net	(18,983)	37,252	(57,728)
Income before income tax expense	1,229,906	1,332,679	1,155,883
Income tax expense	331,333	355,617	365,776
Net income	898,573	977,062	790,107
Net income (loss) attributable to noncontrolling interests, net of tax	(106,700)	6,930	6,940
Net income attributable to Biogen Idec Inc.	$ 1,005,273	$ 970,132	$ 783,167
Basic earnings per share attributable to Biogen Idec Inc.	$ 3.98	$ 3.37	$ 2.67
Diluted earnings per share attributable to Biogen Idec Inc.	$ 3.94	$ 3.35	$ 2.65
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Idec Inc.	252,307	287,356	292,332
Diluted earnings per share attributable to Biogen Idec Inc.	254,867	289,476	294,984

Consolidated Balance Sheets - USD ($) $ in Thousands	12 Months Ended
Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2010	Dec. 31, 2009
Current assets:
Cash and cash equivalents	$ 759,598	$ 581,889
Marketable securities	448,146	681,835
Accounts receivable, net of allowances of $54,922 and $43,818, respectively	605,329	551,208
Due from unconsolidated joint business	222,459	193,789
Inventory	289,066	293,950
Other current assets	215,822	177,924
Total current assets	2,540,420	2,480,595
Marketable securities	743,101	1,194,080
Property, plant and equipment, net	1,641,634	1,637,083
Intangible assets, net	1,772,826	1,871,078
Goodwill	1,146,314	1,138,621
Investments and other assets	248,198	230,397
Total assets	8,092,493	8,551,854
Current liabilities:
Current portion of notes payable, line of credit and other financing arrangements	137,153	19,762
Taxes payable	84,517	75,891
Accounts payable	162,529	118,534
Accrued expenses and other	665,923	500,755
Total current liabilities	1,050,122	714,942
Notes payable and line of credit	1,066,379	1,080,207
Long-term deferred tax liability	200,950	240,618
Other long-term liabilities	325,599	254,205
Total liabilities	$ 2,643,050	$ 2,289,972
Commitments and contingencies (Notes 2, 3, 10, 16, 18, 19, 20, and 21)
Equity:
Preferred stock, par value $0.001 per share	$ 0	$ 0
Common stock, par value $0.0005 per share	124	144
Additional paid-in capital	3,895,103	5,781,920
Accumulated other comprehensive income (loss)	(21,610)	50,496
Retained earnings	1,872,481	1,068,890
Treasury stock, at cost; 7,662 shares and 13,639 shares, respectively	(349,592)	(679,920)
Total Biogen Idec Inc. shareholders' equity	5,396,506	6,221,530
Noncontrolling interests	52,937	40,352
Total equity	5,449,443	6,261,882
Total liabilities and equity	$ 8,092,493	$ 8,551,854

Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands	Dec. 31, 2010	Dec. 31, 2009
Current assets:
Allowance for Doubtful Accounts Receivable, Current	$ 54,922,000	$ 43,818,000
Equity:
Preferred stock, par value	0.001	0.001
Common stock, par value	$ 0.0005	$ 0.0005
Treasury stock, shares	7,662	13,639

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Cash flows from operating activities:
Net income	$ 898,573	$ 977,062	$ 790,107
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization of property, plant and equipment and intangible assets	354,101	427,961	462,059
Acquired in process research and development	271,376		25,000
Share-based compensation	167,826	160,902	146,207
Excess tax benefit from share-based compensation	(13,136)	(3,436)	(27,990)
Deferred income taxes	(81,410)	(137,351)	(139,549)
Write-down of inventory to net realizable value	11,808	16,924	29,850
Impairment of marketable securities, investments and other assets	20,846	16,184	61,644
Non-cash interest (income) expense and foreign exchange remeasurement loss (gain), net	5,808	(7,892)	(4,934)
Cash received upon termination of interest rate swap			53,873
Realized (gain) loss on sale of marketable securities and strategic investments	(16,321)	(23,974)	1,078
(Gain) loss on sale of property, plant and equipment, net	1,643		(9,242)
Changes in operating assets and liabilities, net:
Accounts receivable	(99,227)	(100,442)	(57,565)
Due from unconsolidated joint business	(28,670)	13,136	(40,239)
Inventory	(4,527)	(42,772)	(54,204)
Other assets	(12,584)	22,271	3,711
Accrued expenses and other current liabilities	130,875	(48,942)	146,420
Other liabilities and taxes payable	17,692	(194,733)	176,219
Net cash flows provided by operating activities	1,624,673	1,074,898	1,562,445
Cash flows from investing activities:
Proceeds from sales and maturities of marketable securities	2,668,694	3,319,007	2,941,060
Purchases of marketable securities	(1,988,394)	(3,548,119)	(3,163,824)
Acquisitions	(72,476)		(25,000)
Acquisition of a variable interest entity, net	(84,952)
Purchases of property, plant and equipment	(173,055)	(165,646)	(275,954)
Purchases of other investments	(4,492)	(44,086)	(20,373)
Proceeds from the sale of strategic investments		13,822
Collateral received under securities lending		29,991	178,218
Net cash flows used in investing activities	345,325	(395,031)	(365,873)
Cash flows from financing activities:
Purchase of treasury stock	(2,077,579)	(751,170)	(738,938)
Proceeds from issuance of stock for share-based compensation arrangements	183,486	47,810	178,486
Excess tax benefit from share-based compensation	13,136	3,436	27,990
Change in cash overdraft	11,781	12,275	(498)
Net distributions to noncontrolling interests	(23,475)	4,356	2,047
Repayments of borrowings	(18,073)	(10,867)	(1,512,474)
Proceeds from borrowings			986,980
Net proceeds from financing arrangement for the sale of the San Diego facility	126,980
Repayments on financing arrangement for the sale of the San Diego facility	(1,175)
Obligation under securities lending		(29,991)	(178,218)
Net cash flows provided by (used in) in investing activities	(1,784,919)	(724,151)	(1,234,625)
Net increase (decrease) in cash and cash equivalents	185,079	(44,284)	(38,053)
Effect of exchange rate changes on cash and cash equivalents	(7,370)	3,788	776
Cash and cash equivalents, beginning of the year	581,889	622,385	659,662
Cash and cash equivalents, end of the year	$ 759,598	$ 581,889	$ 622,385

Consolidated Statements of Shareholders' Equity - USD ($) shares in Thousands, $ in Thousands	3 Months Ended				12 Months Ended
	Dec. 31, 2010	Mar. 31, 2010	Dec. 31, 2009	Mar. 31, 2009	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Statement [Line Items]
Beginning Balance		$ 6,261,882		$ 5,833,952	$ 6,261,882	$ 5,833,952	$ 5,554,023
Comprehensive income:
Net income	$ 271,800	220,000	$ 306,000	246,600	898,573	977,062	790,107
Unrealized gains (losses) on securities available for sale, net of tax of $1,123, $380 and $689 for 2008, 2009 and 2010, respectively					1,144	795	(67)
Unrealized gains (losses) on foreign currency forward contracts, net of tax of $1,522, $3,582 and $964 for 2008, 2009 and 2010, respectively					(11,269)	41,668	(36,140)
Unrealized gains (losses) on pension benefit obligation, net of tax of $0, $67 and $0 for 2008, 2009 and 2010, respectively					(1,942)	501	(43)
Currency translation adjustment					(62,279)	19,835	(54,948)
Total comprehensive income					824,227	1,039,861	698,909
Fair value of assets and liabilities acquired and assigned to noncontrolling interests (Note 18)					145,000
Distribution to noncontrolling interests					(33,891)	(2,832)	(2,817)
Capital contribution from noncontrolling interests					2,488	7,188	4,864
Deconsolidation of Cardiokine Biopharma LLC					7,928
Repurchase of common stock for Treasury, at cost					(2,077,579)	(751,170)	(738,938)
Issuance of common stock from conversion of subordinated notes payable							227
Issuance of common and treasury stock under stock option and stock purchase plans							178,486
Issuance of treasury stock under stock option and stock purchase plans					183,486	47,810
Issuance of treasury stock under stock award plans					(54,840)	(43,305)	(44,395)
Compensation expense related to share-based payments					171,435	167,207	153,748
Tax benefit from share-based payments					19,307	(36,829)	29,845
Ending Balance	5,449,443		6,261,882		5,449,443	6,261,882	5,833,952
Biogen Idec Inc. Shareholders' Equity
Statement [Line Items]
Beginning Balance		6,221,530		5,806,083	6,221,530	5,806,083	5,534,295
Comprehensive income:
Net income					1,005,273	970,132	783,167
Unrealized gains (losses) on securities available for sale, net of tax of $1,123, $380 and $689 for 2008, 2009 and 2010, respectively					1,144	795	(67)
Unrealized gains (losses) on foreign currency forward contracts, net of tax of $1,522, $3,582 and $964 for 2008, 2009 and 2010, respectively					(11,269)	41,668	(36,140)
Unrealized gains (losses) on pension benefit obligation, net of tax of $0, $67 and $0 for 2008, 2009 and 2010, respectively					(1,942)	501	(43)
Currency translation adjustment					(60,039)	18,638	(54,102)
Total comprehensive income					933,167	1,031,734	692,815
Repurchase of common stock for Treasury, at cost					(2,077,579)	(751,170)	(738,938)
Issuance of common stock from conversion of subordinated notes payable							227
Issuance of common and treasury stock under stock option and stock purchase plans							178,486
Issuance of treasury stock under stock option and stock purchase plans					183,486	47,810
Issuance of treasury stock under stock award plans					(54,840)	(43,305)	(44,395)
Compensation expense related to share-based payments					171,435	167,207	153,748
Tax benefit from share-based payments					19,307	(36,829)	29,845
Ending Balance	5,396,506		6,221,530		5,396,506	6,221,530	5,806,083
Preferred Stock
Statement [Line Items]
Beginning Balance		$ 0		$ 0	$ 0	$ 0	$ 0
Beginning Balance, shares		8		8	8	8	8
Comprehensive income:
Ending Balance	$ 0		$ 0		$ 0	$ 0	$ 0
Ending Balance, shares	8		8		8	8	8
Common Stock
Statement [Line Items]
Beginning Balance		$ 144		$ 149	$ 144	$ 149	$ 147
Beginning Balance, shares		288,494		297,253	288,494	297,253	295,698
Comprehensive income:
Retirement of common stock pursuant to 2009 and 2010 share repurchase plan					$ (20)	$ (5)
Retirement of common stock pursuant to 2009 and 2010 share repurchase plan, shares					(40,294)	(8,759)
Issuance of common stock from conversion of subordinated notes payable, shares							16
Issuance of common and treasury stock under stock option and stock purchase plans							$ 1
Issuance of common and treasury stock under stock option and stock purchase plans, shares							852
Issuance of treasury stock under stock award plans							$ 1
Issuance of treasury stock under stock award plans, shares							688
Forfeiture of common stock under restricted stock plan, shares							(1)
Ending Balance	$ 124		$ 144		$ 124	$ 144	$ 149
Ending Balance, shares	248,200		288,494		248,200	288,494	297,253
Additional Paid-in Capital
Statement [Line Items]
Beginning Balance		$ 5,781,920		$ 6,073,957	$ 5,781,920	$ 6,073,957	$ 5,807,071
Comprehensive income:
Retirement of common stock pursuant to 2009 and 2010 share repurchase plan					(2,077,559)	(422,415)
Issuance of common stock from conversion of subordinated notes payable							227
Issuance of common and treasury stock under stock option and stock purchase plans							34,297
Issuance of treasury stock under stock award plans							(29,800)
Compensation expense related to share-based payments					171,435	167,207	153,748
Tax benefit from share-based payments					19,307	(36,829)	29,845
Treasury stock reclassifications							78,569
Ending Balance	$ 3,895,103		$ 5,781,920		3,895,103	5,781,920	6,073,957
Accumulated Other Comprehensive Income
Statement [Line Items]
Beginning Balance		50,496		(11,106)	50,496	(11,106)	79,246
Comprehensive income:
Unrealized gains (losses) on securities available for sale, net of tax of $1,123, $380 and $689 for 2008, 2009 and 2010, respectively					1,144	795	(67)
Unrealized gains (losses) on foreign currency forward contracts, net of tax of $1,522, $3,582 and $964 for 2008, 2009 and 2010, respectively					(11,269)	41,668	(36,140)
Unrealized gains (losses) on pension benefit obligation, net of tax of $0, $67 and $0 for 2008, 2009 and 2010, respectively					(1,942)	501	(43)
Currency translation adjustment					(60,039)	18,638	(54,102)
Ending Balance	(21,610)		50,496		(21,610)	50,496	(11,106)
(Accumulated Deficit) / Retained Earnings
Statement [Line Items]
Beginning Balance		1,068,890		270,180	1,068,890	270,180	(352,169)
Comprehensive income:
Net income					1,005,273	970,132	783,167
Issuance of common and treasury stock under stock option and stock purchase plans							(56,223)
Issuance of treasury stock under stock option and stock purchase plans					(28,632)	(27,191)
Issuance of treasury stock under stock award plans					(173,050)	(144,231)	(26,026)
Treasury stock reclassifications							(78,569)
Ending Balance	1,872,481		1,068,890		1,872,481	1,068,890	270,180
Treasury Stock
Statement [Line Items]
Beginning Balance		$ (679,920)		$ (527,097)	$ (679,920)	$ (527,097)	$ 0
Beginning Balance, shares		(13,639)		(9,207)	(13,639)	(9,207)	0
Comprehensive income:
Repurchase of common stock for Treasury, at cost					$ (2,077,579)	$ (751,170)	$ (738,938)
Repurchase of common stock for Treasury, at cost, shares					(40,294)	(15,982)	(12,778)
Retirement of common stock pursuant to 2009 and 2010 share repurchase plan					$ 2,077,579	$ 422,420
Retirement of common stock pursuant to 2009 and 2010 share repurchase plan, shares					40,294	8,759
Issuance of common and treasury stock under stock option and stock purchase plans							$ 200,411
Issuance of common and treasury stock under stock option and stock purchase plans, shares							3,380
Issuance of treasury stock under stock option and stock purchase plans					$ 212,118	$ 75,001
Issuance of treasury stock under stock option and stock purchase plans, shares					4,020	1,181
Issuance of treasury stock under stock award plans					$ 118,210	$ 100,926	$ 11,430
Issuance of treasury stock under stock award plans, shares					1,957	1,610	191
Ending Balance	$ (349,592)		$ (679,920)		$ (349,592)	$ (679,920)	$ (527,097)
Ending Balance, shares	(7,662)		(13,639)		(7,662)	(13,639)	(9,207)
Noncontrolling Interests
Statement [Line Items]
Beginning Balance		$ 40,352		$ 27,869	$ 40,352	$ 27,869	$ 19,728
Comprehensive income:
Net income					(106,700)	6,930	6,940
Currency translation adjustment					(2,240)	1,197	(846)
Total comprehensive income					(108,940)	8,127	6,094
Fair value of assets and liabilities acquired and assigned to noncontrolling interests (Note 18)					145,000
Distribution to noncontrolling interests					(33,891)	(2,832)	(2,817)
Capital contribution from noncontrolling interests					2,488	7,188	4,864
Deconsolidation of Cardiokine Biopharma LLC					7,928
Ending Balance	$ 52,937		$ 40,352		$ 52,937	$ 40,352	$ 27,869

Consolidated Statements of Shareholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Comprehensive income:
Tax effect on unrealized gains (losses) recognized on securities available for sale	$ 689	$ 380	$ 1,123
Tax effect of unrealized gains (losses) recognized on foreign currency forward contracts	964	3,582	1,522
Tax effect of unrealized gains (losses) recognized on pension benefit obligation	0	67	0
Biogen Idec Inc. Shareholders' Equity
Comprehensive income:
Tax effect on unrealized gains (losses) recognized on securities available for sale	689	380	1,123
Tax effect of unrealized gains (losses) recognized on foreign currency forward contracts	964	3,582	1,522
Tax effect of unrealized gains (losses) recognized on pension benefit obligation	0	67	0
Accumulated Other Comprehensive Income
Comprehensive income:
Tax effect on unrealized gains (losses) recognized on securities available for sale	689	380	1,123
Tax effect of unrealized gains (losses) recognized on foreign currency forward contracts	964	3,582	1,522
Tax effect of unrealized gains (losses) recognized on pension benefit obligation	$ 0	$ 67	$ 0

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2010

Summary of Significant Accounting Policies [Abstract]

Summary of Significant Accounting Policies


1.	Summary of Significant Accounting Policies

Business Overview

Biogen Idec is a global biotechnology company focused on discovering, developing, manufacturing and marketing products for the treatment of serious diseases with a focus on neurological disorders. We currently have four marketed products: AVONEX, RITUXAN, TYSABRI, and FUMADERM. Our marketed products are used for the treatment of multiple sclerosis (MS), non-Hodgkin’s lymphoma (NHL), rheumatoid arthritis (RA), Crohn’s disease, chronic lymphocytic leukemia (CLL) and psoriasis.

Consolidation

Our consolidated financial statements reflect our financial statements, those of our wholly-owned subsidiaries and those of certain variable interest entities in which we are the primary beneficiary. For such consolidated entities in which we own less than a 100% interest, we record net income (loss) attributable to noncontrolling interest in our consolidated statements of income equal to the percentage of the economic or ownership interest retained in the collaborative arrangement or joint venture by the respective noncontrolling parties. All material intercompany balances and transactions have been eliminated in consolidation.

Effective January 1, 2010, we adopted a newly issued accounting standard which provides updated guidance for the consolidation of variable interest entities and requires an enterprise to determine whether its variable interest or interests give it a controlling financial interest in a variable interest entity. The adoption of this standard did not have an impact on our financial position or results of operations. This new consolidation guidance for variable interest entities replaces the prior quantitative approach for identifying which enterprise should consolidate a variable interest entity, which was based on which enterprise was exposed to a majority of the risks and rewards, with a qualitative approach, based on which enterprise has both (1) the power to direct the economically significant activities of the entity and (2) the obligation to absorb losses of, or the right to receive benefits from, the entity that could potentially be significant to the variable interest entity. These considerations impact the way we account for our existing collaborative and joint venture relationships and determine the consolidation of companies or entities with which we have collaborative or other arrangements. Determination about whether an enterprise should consolidate a variable interest entity is required to be evaluated continuously as changes to existing relationships or future transactions may result in us consolidating or deconsolidating our partner(s) to collaborations and other arrangements.

Use of Estimates

The preparation of consolidated financial statements in accordance with U.S. GAAP requires management to make estimates and judgments that may affect the reported amounts of assets, liabilities, revenues and expenses, and related disclosure of contingent assets and liabilities. On an on-going basis, we evaluate our estimates and judgments and methodologies, including those related to revenue recognition and related allowances, our collaborative relationships, clinical trial expenses, the consolidation of variable interest entities, the valuation of contingent consideration resulting from a business combination, the valuation of acquired intangible assets, including in process research and development, inventory, impairment and amortization of long-lived assets including intangible assets, impairments of goodwill, share-based compensation, income taxes including the valuation allowance for deferred tax assets, valuation of investments, derivatives and hedging activities, contingencies, litigation, and restructuring charges. We base our estimates on historical experience and on various other assumptions that are believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results may differ from these estimates under different assumptions or conditions.

Revenue Recognition

We recognize revenue when all of the following criteria are met: persuasive evidence of an arrangement exists; delivery has occurred or services have been rendered; the seller’s price to the buyer is fixed or determinable; and collectibility is reasonably assured.

Product Revenues

Revenues from product sales are recognized when title and risk of loss have passed to the customer, which is typically upon delivery. However, sales of TYSABRI in the U.S. are recognized on the “sell-through” model, that is, upon shipment of the product by Elan Pharma International, Ltd. (Elan), an affiliate of Elan Corporation, plc, to its third party distributor rather than upon shipment to Elan.

Product revenues are recorded net of applicable reserves for discounts and allowances. Our product revenue reserves are based on estimates of the amounts earned or to be claimed on the related sales. These estimates take into consideration our historical experience, current contractual requirements and statutory requirements, specific known market events and trends and forecasted customer buying patterns.

Reserves for Discounts and Allowances

We establish reserves for trade term discounts, wholesaler incentives, Medicaid rebates, Veterans Administration (VA) and Public Health Service (PHS) discounts, managed care rebates, product returns and other applicable allowances. Reserves established for these discounts and allowances are classified as reductions of accounts receivable (if the amount is payable to our customer) or a liability (if the amount is payable to a party other than our customer). In addition, we distribute no-charge product to qualifying patients under our patient assistance and patient replacement goods program. This program is administered through one of our distribution partners, which ships product for qualifying patients from its own inventory received from us. Gross revenue and the related reserves are not recorded on product shipped under this program and cost of sales is recorded when the product is shipped.

Product revenue reserves are categorized as follows: discounts, contractual adjustments and returns.

Discount reserves include trade term discounts and wholesaler incentives. Trade term discounts and wholesaler incentive reserves primarily relate to estimated obligations for credits to be granted to wholesalers for remitting payment on their purchases within established incentive periods and credits to be granted to wholesalers for compliance with various contractually-defined inventory management practices, respectively. We determine these reserves based on our experience, including the timing of customer payments.

Contractual adjustment reserves primarily relate to Medicaid and managed care rebates, VA and PHS discounts and other applicable allowances.


	•	Medicaid rebate reserves relate to our estimated obligations to states under established reimbursement arrangements. Rebate accruals are recorded in the same period the related revenue is recognized resulting in a reduction of product revenue and the establishment of a liability which is included in other current liabilities. Our liability for Medicaid rebates consists of estimates for claims that a state will make for the current quarter, claims for prior quarters that have been estimated for which an invoice has not been received, invoices received for claims from the prior quarters that have not been paid and an estimate of potential claims that will be made for inventory that exists in the distribution channel at period end.

	•	VA rebates or chargeback reserves represent our estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices we charge to wholesalers which provide those products. The wholesaler charges us for the difference between what the wholesaler pays for the products and the ultimate selling price to the qualified healthcare providers. Rebate and chargeback reserves are established in the same period as the related revenue is recognized resulting in a reduction in product revenue and accounts receivable. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider from the wholesaler, and we generally issue credits for such amounts within a few weeks of the wholesaler notifying us about the resale. Our reserves for VA and chargebacks consists of amounts that we expect to issue for inventory that exists at the wholesalers that we expect will be sold to qualified healthcare providers and chargebacks that wholesalers have claimed for which we have not issued a credit.


	•	Managed care rebate reserves represent our estimated obligations to third parties, primarily pharmacy benefit managers. Rebate accruals are recorded in the same period the related revenue is recognized resulting in a reduction of product revenue and the establishment of a liability which is included in accrued expenses and other current liabilities. These rebates result from performance-based goals that are primarily based on attaining contractually specified sales volumes and growth. The calculation of the accrual for these rebates is based on an estimate of the customer’s buying patterns and the resulting applicable contractual rebate rate(s) to be earned over a contractual period.

Product return reserves are established for returns expected to be made by wholesalers and patients and are recorded in the period the related revenue is recognized, resulting in a reduction to product revenue in the period of sale. In accordance with our standard contractual terms, wholesalers are permitted to return product for reasons such as damaged or expired product. Expired product return reserves are estimated through a comparison of historical return data to their related sales on a production lot basis. Historical rates of return are determined for each product and are adjusted for known or expected changes in the marketplace specific to each product.

In addition to the discounts and rebates described above and classified as a reduction of revenue, we also maintain certain customer service contracts with distributors and other customers in the distribution channel that provide us with inventory management and distribution services. We have established the fair value of these services and classified these customer service contracts as sales and marketing expense. If we had concluded that we did not receive a separate identifiable benefit or have sufficient evidence that the fair value did not exist for these services, we would have been required to classify these costs as a reduction of revenue.

Revenues from Unconsolidated Joint Business

We collaborate with Genentech on the development and commercialization of RITUXAN. Revenues from unconsolidated joint business consist of (1) our share of pre-tax co-promotion profits in the U.S.; (2) reimbursement of our selling and development expense in the U.S.; and (3) revenue on sales of RITUXAN in the rest of world, which consists of our share of pretax co-promotion profits in Canada and royalty revenue on sales of RITUXAN outside the U.S. and Canada by F. Hoffmann-La Roche Ltd. (Roche) and its sublicensees. Pre-tax co-promotion profits are calculated and paid to us by Genentech in the U.S. and by Roche in Canada. Pre-tax co-promotion profits consist of U.S. and Canadian sales of RITUXAN to third-party customers net of discounts and allowances less the cost to manufacture RITUXAN, third-party royalty expenses, distribution, selling and marketing, and joint development expenses incurred by Genentech, Roche and us. We record our share of the pretax co-promotion profits in Canada and royalty revenues on sales of RITUXAN outside the U.S. on a cash basis. Additionally, our share of the pretax co-promotion profits in the U.S. includes estimates supplied by Genentech. Actual results may ultimately differ from our estimates.

Royalty Revenues

We receive royalty revenues on sales by our licensees of other products covered under patents that we own. There are no future performance obligations on our part under these license arrangements. We record these revenues based on estimates of the sales that occurred during the relevant period. The relevant period estimates of sales are based on interim data provided by licensees and analysis of historical royalties that have been paid to us, adjusted for any changes in facts and circumstances, as appropriate. We maintain regular communication with our licensees in order to assess the reasonableness of our estimates. Differences between actual royalty revenues and estimated royalty revenues are adjusted for in the period in which they become known, typically the following quarter. Historically, adjustments have not been material when compared to actual amounts paid by licensees. If we are unable to accurately estimate revenue, then we record revenues on a cash basis.

Milestone Revenues

Under the terms of our collaboration agreement with Elan, once sales of TYSABRI exceeded specific thresholds, Elan was required to make milestone payments to us in order to continue sharing equally in the collaboration’s results. These amounts, totaling $125.0 million, were recorded as deferred revenue upon receipt and are recognized as revenue in our consolidated statements of income based on the ratio of units shipped in the current period over the total units expected to be shipped over the remaining term of the collaboration agreement. As of December 31, 2010, there is $108.3 million remaining to the amortized.

Multiple-Deliverable Revenue Arrangements

During the third quarter of 2010, in conjunction with our entering into a new arrangement to offer contract manufacturing services, we elected the early adoption of Accounting Standards Update (ASU) No. 2009-13, Multiple-Deliverable Revenue Arrangements (ASU 2009-13). ASU 2009-13, amends existing revenue recognition accounting pronouncements and provides accounting principles and application guidance on whether multiple deliverables exist, how the arrangement should be separated, and the consideration allocated. This guidance eliminates the requirement to establish the fair value of undelivered products and services and instead provides for separate revenue recognition based upon management’s best estimate of the selling price for an undelivered item when there is no other means to determine the fair value of that undelivered item. Previous accounting principles required that the fair value of the undelivered item be the price of the item either sold in a separate transaction between unrelated third parties or the price charged for each item when the item is sold separately by the vendor. The early adoption of this standard requires the disclosure of the effect of this guidance effective as of January 1, 2010, as applied to all previously reported interim periods in the fiscal year of adoption. Our adoption of this standard on January 1, 2010 had no impact on our reported financial position or results of operations, since we had not previously recorded any revenue in accordance with revenue recognition rules for multiple deliverables as described in ASU 2009-13 or its predecessor pronouncements.

Fair Value Measurements

Effective January 1, 2009, we adopted a newly issued accounting standard for fair value measurements of all nonfinancial assets and nonfinancial liabilities not recognized or disclosed at fair value in the financial statements on a recurring basis. The adoption of the accounting standard for these assets and liabilities did not have a material impact on our financial position or results of operations but may impact us in subsequent periods and require additional disclosures.

We have certain financial assets and liabilities recorded at fair value which have been classified as Level 1, 2 or 3 within the fair value hierarchy as described in the accounting standards for fair value measurements.


	•	Level 1 — Fair values are determined utilizing quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access;

	•	Level 2 — Fair values are determined by utilizing quoted prices for identical or similar assets and liabilities in active markets or other market observable inputs such as interest rates, yield curves and foreign currency spot rates; and

	•	Level 3 — Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable.

The carrying amounts reflected in the consolidated balance sheets for cash equivalents, current accounts receivable, due from unconsolidated joint business, other current assets, accounts payable, and accrued expenses and other, approximate fair value due to their short-term maturities.

In January 2010, we adopted a newly issued accounting standard which requires additional disclosure about the amounts of and reasons for significant transfers in and out of Level 1 and Level 2 fair value measurements. This standard also clarified existing disclosure requirements related to the level of disaggregation of fair value measurements for each class of assets and liabilities and requires disclosures about inputs and valuation techniques used to measure fair value for both recurring and nonrecurring Level 2 and Level 3 measurements. In addition, effective for interim and annual periods beginning after December 15, 2010, this standard further requires an entity to present disaggregated information about activity in Level 3 fair value measurements on a gross basis, rather than as one net amount. As this newly issued accounting standard only requires enhanced disclosure, the adoption of this standard did not impact our financial position or results of operations and will not affect them in the future.

Cash and Cash Equivalents

We consider only those investments which are highly liquid, readily convertible to cash and that mature within three months from date of purchase to be cash equivalents. As of December 31, 2010 and 2009, cash equivalents were comprised of money market funds and commercial paper.

Accounts Receivable

Our accounts receivable primarily arise from product sales and primarily represent amounts due from our wholesale distributors, large pharmaceutical companies, public hospitals and other government entities. We monitor the financial performance and credit worthiness of our large customers so that we can properly assess and respond to changes in their credit profile. We provide reserves against trade receivables for estimated losses that may result from a customer’s inability to pay. Amounts determined to be uncollectible are charged or written-off against the reserve. To date, such losses have not exceeded management’s estimates.

Concentration of Credit Risk

Financial instruments that potentially subject us to concentrations of credit risk include cash and cash equivalents, investments, derivatives, and accounts receivable. We attempt to minimize the risks related to cash and cash equivalents and investments by using highly-rated financial institutions that invest in a broad and diverse range of financial instruments as previously defined by us. We have established guidelines relative to credit ratings and maturities intended to safeguard principal balances and maintain liquidity. Our investment portfolio is maintained in accordance with our investment policy, which defines allowable investments, specifies credit quality standards and limits the credit exposure of any single issuer. We minimize credit risk resulting from derivatives instruments by choosing only highly rated financial institutions as counterparties.

Concentrations of credit risk with respect to receivables, which are typically unsecured, are limited due to the wide variety of customers and markets using our products, as well as their dispersion across many different geographic areas. The majority of our accounts receivable arise from product sales in the United States and Europe and have standard payment terms which are generally between 30 and 90 days. We continue to monitor economic conditions, including the volatility associated with international economies, and associated impacts on the relevant financial markets and our business, especially in light of the global economic downturn. The credit and economic conditions within Italy, Spain, Portugal and Greece, among other members of the European Union, have deteriorated throughout 2010. These conditions have resulted in, and may continue to result in, an increase in the average length of time that it takes to collect on our accounts receivable outstanding in these countries.

As of December 31, 2010, our accounts receivable balances in Italy, Spain, Portugal and Greece were $118.0 million, $100.6 million, $23.3 million and $3.9 million, respectively, totaling approximately $245.8 million. Approximately $45.0 million of this amount was outstanding for greater than one year, none of which related to our Greek distributor. As of December 31, 2010, we had $50.1 million of receivables that are expected to be collected beyond one year, which are included as a component of investments and other assets within our consolidated balance sheet. To date, we have not experienced any significant losses or write-offs with respect to the collection of our accounts receivable in these countries.

As of December 31, 2010 and 2009, one wholesale distributor accounted for approximately 11.5% and 8.1% of consolidated receivables, respectively.

Inventory

Inventories are stated at the lower of cost or market with cost determined under the first-in, first-out (FIFO) method. Included in inventory are raw materials used in the production of pre-clinical and clinical products, which are expensed as research and development costs when consumed.

Capitalization of Inventory Costs

We capitalize inventory costs associated with our products prior to regulatory approval, when, based on management’s judgment, future commercialization is considered probable and the future economic benefit is expected to be realized. We consider numerous attributes in evaluating whether the costs to manufacture a particular product should be capitalized as an asset. We assess the regulatory approval process and where the particular product stands in relation to that approval process, including any known safety or efficacy concerns, potential labeling restrictions and other impediments to approval. We evaluate our anticipated research and development initiatives and constraints relating to the product and the indication in which it will be used. We consider our manufacturing environment including our supply chain in determining logistical constraints that could hamper approval or commercialization. We consider the shelf life of the product in relation to the expected timeline for approval and we consider patent related or contract issues that may prevent or delay commercialization. We also base our judgment on the viability of commercialization, trends in the marketplace and market acceptance criteria. Finally, we consider the reimbursement strategies that may prevail with respect to the product and assess the economic benefit that we are likely to realize.

We expense previously capitalized costs related to pre-approval inventory upon a change in such judgment, due to, among other potential factors, a denial or delay of approval by necessary regulatory bodies. As of December 31, 2010 and 2009, the carrying value of our inventory did not include any costs associated with products that had not yet received regulatory approval.

Obsolescence and Unmarketable Inventory

We periodically review our inventories for excess or obsolete inventory and write-down obsolete or otherwise unmarketable inventory to its estimated net realizable value. If the actual net realizable value is less than that estimated by us, or if it is determined that inventory utilization will further diminish based on estimates of demand, additional inventory write-downs may be required. Additionally, our products are subject to strict quality control and monitoring which we perform throughout the manufacturing process. In the event that certain batches or units of product no longer meet quality specifications or become obsolete due to expiration, we will record a charge to cost of sales to write-down any obsolete or otherwise unmarketable inventory to its estimated net realizable value. In all cases product inventory is carried at the lower of cost or its estimated net realizable value. Amounts written-down to unmarketable inventory are charged to cost of sales, excluding amortization of acquired intangible assets.

Marketable Securities and Other Investments

Marketable Debt Securities

Available-for-sale debt securities are recorded at fair market value and unrealized gains and losses are included in accumulated other comprehensive income (loss) in equity, net of related tax effects, unless the security has experienced a credit loss, we have determined that we have the intent to sell the security or we have determined that it is more likely than not that we will have to sell the security before its expected recovery. Realized gains and losses are reported in other income (expense), net, on a specific identification basis.

Strategic Investments

As part of our strategic product development efforts, we invest in equity securities of certain biotechnology companies. These investments are known as strategic investments and are classified as available-for-sale and accounted for as marketable equity investments or as cost investments based upon our ownership percentage and other factors that suggest we have significant influence and are included in investments and other assets within our consolidated balance sheet. When assessing whether a decline in the fair value of a strategic investment below our cost basis is other-than-temporary, we consider the fair market value of the security, the duration of the security’s decline, and prospects for the underlying business, including favorable or adverse clinical trial results, new product initiatives and new collaborative agreements with the companies in which we have invested.

Non-Marketable Equity Securities

We also invest in equity securities of companies whose securities are not publicly traded and where fair value is not readily available. These investments are recorded using either the cost method or the equity method of accounting, depending on our ownership percentage and other factors that suggest we have significant influence. We monitor these investments to evaluate whether any decline in their value has occurred that would be other-than-temporary, based on the implied value of recent company financings, public market prices of comparable companies, and general market conditions and are included in investments and other assets within our consolidated balance sheet.

Evaluating Investments for Other-than-Temporary Impairments

We conduct periodic reviews to identify and evaluate each investment that has an unrealized loss, in accordance with the meaning of other-than-temporary impairment and its application to certain investments. An unrealized loss exists when the current fair value of an individual security is less than its amortized cost basis. Unrealized losses on available-for-sale securities that are determined to be temporary, and not related to credit loss, are recorded, net of tax, in accumulated other comprehensive income.

For available-for-sale debt securities with unrealized losses, management performs an analysis to assess whether we intend to sell or whether we would more likely than not be required to sell the security before the expected recovery of the amortized cost basis. Where we intend to sell a security, or may be required to do so, the security’s decline in fair value is deemed to be other-than-temporary and the full amount of the unrealized loss is reflected within earnings as an impairment loss.

Regardless of our intent to sell a security, we perform additional analysis on all securities with unrealized losses to evaluate losses associated with the creditworthiness of the security. Credit losses are identified where we do not expect to receive cash flows sufficient to recover the amortized cost basis of a security.

For equity securities, when assessing whether a decline in fair value below our cost basis is other-than-temporary, we consider the fair market value of the security, the duration of the security’s decline, and the financial condition of the issuer. We then consider our intent and ability to hold the equity security for a period of time sufficient to recover our carrying value. Where we have determined that we lack the intent and ability to hold an equity security to its expected recovery, the security’s decline in fair value is deemed to be other-than-temporary and is reflected within earnings as an impairment loss.

Property, Plant and Equipment

Property, plant and equipment are carried at cost, subject to review for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. The cost of normal, recurring, or periodic repairs and maintenance activities related to property, plant and equipment are expensed as incurred. The cost for planned major maintenance activities, include the related acquisition or construction of assets, is capitalized if the repair will result in future economic benefits.

Interest costs incurred during the construction of major capital projects are capitalized until the underlying asset is ready for its intended use, at which point the interest costs are amortized as depreciation expense over the life of the underlying asset. We also capitalize certain direct and incremental costs associated with the validation effort required for licensing by regulatory agencies of manufacturing equipment for the production of a commercially approved drug. These costs include primarily direct labor and material and are incurred in preparing the equipment for its intended use. The validation costs are amortized over the life of the related equipment.

We also capitalize certain internal use computer software development costs. If the software is an integral part of production assets, these costs are included in machinery and equipment and are amortized on a straight-line basis over the estimated useful lives of the related software, which generally range from three to five years.

We generally depreciate or amortize the cost of our property, plant and equipment using the straight-line method over the estimated useful lives of the respective assets, which are summarized as follows:


Asset Category		Useful Lives

Land		Not depreciated
Buildings		15 to 40 years
Leasehold Improvements		Lesser of the useful life or the term of the respective lease
Furniture and Fixtures		7 years
Machinery and Equipment		6 to 15 years
Computer Software and Hardware		3 to 5 years

When we dispose of property, plant and equipment, we remove the associated cost and accumulated depreciation from the related accounts on our consolidated balance sheet and include any resulting gain or loss in our consolidated statement of income.

Intangible Assets

Our intangible assets consist of patents, licenses, core developed technology, in process research and development acquired after January 1, 2009, trademarks, tradenames, assembled workforce and distribution rights. The majority of our intangible assets were recorded in connection with the merger of Biogen, Inc. and IDEC Pharmaceuticals Corporation in 2003. Our intangible assets are recorded at fair value at the time of their acquisition and are stated within our consolidated balance sheets net of accumulated amortization and impairments.

We amortize intangible assets over their estimated useful lives using the economic use method unless the straight-line method results in significantly greater amortization. Our amortization policy reflects the pattern that the economic benefits of the intangible assets are consumed. The useful lives of our intangible assets are primarily based on the legal or contractual life of the underlying patent or contract, which does not include additional years for the potential extension or renewal of the contract or patent. Intangible assets related to patents, licenses, core developed technology, assembled workforce, and distribution rights are amortized over their remaining estimated useful lives. Intangible assets related to trademarks, tradenames and in process research and development prior to commercialization are not amortized because they have indefinite lives, but they are subject to review for impairment. We review our intangible assets with indefinite lives for impairment annually, as of October 31, and whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable.

Our most significant intangible asset is the core technology related to our AVONEX product. Our amortization policy reflects our belief that the economic benefit of our core technology is consumed as revenue is generated from AVONEX. We refer to this amortization methodology as the economic consumption model, which involves calculating a ratio of actual current period sales to total anticipated sales for the life of the product and applying this ratio to the carrying amount of the intangible asset. An analysis of the anticipated lifetime revenue of AVONEX is performed at least annually during our long range planning cycle, and this analysis serves as the basis for the calculation of our economic consumption amortization model. Although we believe this process has allowed us to reliably determine the best estimate of the pattern in which we will consume the economic benefits of our core technology intangible asset, the model could result in deferring amortization charges to future periods in certain instances, due to continued sales of the product at a nominal level after patent expiration or otherwise. In order to ensure that amortization charges are not unreasonably deferred to future periods, we compare the amount of amortization determined under the economic consumption model against the minimum amount of amortization recalculated each year under the straight-line method. Amortization is then recorded based upon the higher of the amount of amortization determined under the economic consumption model or the minimum amortization amount determined under the straight-line method.

We monitor events and expectations on product performance to identify circumstances which may result in our inability to recover the carrying value of these assets. If there are any indications that the assumptions underlying our most recent analysis would be different than those utilized within our current estimates, our analysis would be updated and may result in a significant change in the anticipated lifetime revenue of AVONEX determined during our most recent annual review. If the AVONEX ’755 Patent that was issued in September 2009 was invalidated we may have to substantially increase the amount of related amortization expense compared to previous periods.

Impairment of Long-Lived Assets

Long-lived assets to be held and used, including property, plant and equipment as well as intangible assets, are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable such as:


	•	a significant decline in the observable market value of an asset;

	•	a significant change in the extent or manner in which an asset is used; or

	•	a significant adverse change that would indicate that the carrying amount of an asset or group of assets is not recoverable.

Determination of recoverability is based on an estimate of undiscounted future cash flows resulting from the use of the asset and its eventual disposition. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their estimated fair values. Long-lived assets to be disposed of are carried at fair value less costs to sell.

Goodwill

Goodwill relates largely to amounts that arose in connection with the merger of Biogen, Inc. and IDEC Pharmaceuticals Corporation and represents the difference between the purchase price and the fair value of the identifiable tangible and intangible net assets when accounted for using the purchase method of accounting. Goodwill is not amortized, but is subject to periodic review for impairment. Goodwill is reviewed annually, as of October 31, and whenever events or changes in circumstances indicate that the carrying value of the goodwill might not be recoverable.

We apply a two-step impairment test. In the first step, we compare the fair value of our reporting unit to its carrying value. If the carrying value of the net assets assigned to the reporting unit exceeds the fair value of our reporting unit, then the second step of the impairment test is performed in order to determine the implied fair value of our reporting unit’s goodwill. If the carrying value of our reporting unit’s goodwill exceeds its implied fair value, then the company records an impairment loss equal to the difference. As described in Note 24, Segment Information to these consolidated financial statements, we operate in one business segment which we consider our only reporting unit.

Acquired In Process Research and Development (IPR&D)

Acquired IPR&D represents the fair value assigned to research and development assets that we acquire that have not been completed at the date of acquisition. The value assigned to acquired IPR&D is determined by estimating the costs to develop the acquired technology into commercially viable products, estimating the resulting revenue from the projects, and discounting the net cash flows to present value. The revenue and costs projections used to value acquired IPR&D were, as applicable, reduced based on the probability of developing a new drug. Additionally, the projections considered the relevant market sizes and growth factors, expected trends in technology, and the nature and expected timing of new product introductions by us and our competitors. The resulting net cash flows from such projects are based on management’s estimates of cost of sales, operating expenses, and income taxes from such projects. The rates utilized to discount the net cash flows to their present value were commensurate with the stage of development of the projects and uncertainties in the economic estimates used in the projections described above.

Prior to January 1, 2009, we measured acquired IPR&D in a business combination at fair value and expensed it on acquisition date if that technology lacked an alternative future use, or capitalized it as an intangible asset if certain criteria were met; however, effective January 1, 2009, if we are purchasing a business, the acquired IPR&D is measured at fair value, capitalized as an intangible asset and tested for impairment at least annually until commercialization, after which time the IPR&D is amortized over its estimated useful life. If we acquire an asset or group of assets, that do not meet the definition of a business under applicable accounting standards; then the acquired IPR&D is expensed on its acquisition date. Future costs to develop these assets are recorded to expense as they are incurred if the technology lacks alternative future uses.

Valuation of Contingent Consideration Resulting from a Business Combination

For acquisitions completed after January 1, 2009, we record contingent consideration resulting from a business combination at its fair value on the acquisition date. Each reporting period thereafter, we revalue these obligations and record increases or decreases in their fair value as an adjustment to contingent consideration expense within the consolidated statement of income. Changes in the fair value of the contingent consideration obligations can result from adjustments to the discount rates and periods, updates in the assumed achievement or timing of any development milestones or changes in the probability of certain clinical events and changes in the assumed probability associated with regulatory approval. Significant judgment is employed in determining the appropriateness of these assumptions as of the acquisition date and for each subsequent period. Accordingly, any change in the assumptions described above, could have a material impact on the amount of contingent consideration expense we record in any given period.

Derivative Instruments and Hedging Activities

We recognize all derivative instruments as either assets or liabilities at fair value in our consolidated balance sheets. Changes in the fair value of derivatives are recorded each period in current earnings or accumulated other comprehensive income (loss), depending on whether a derivative is designated as part of a hedge transaction and, if it is, the type of hedge transaction. We classify the cash flows from these instruments in the same category as the cash flows from the hedged items. We do not hold or issue derivative instruments for trading or speculative purposes.

We assess, both at inception and on an ongoing basis, whether the derivatives that are used in hedging transactions are highly effective in offsetting the changes in cash flows or fair values of the hedged items. We also assess hedge ineffectiveness on a quarterly basis and record the gain or loss related to the ineffective portion to current earnings to the extent significant. If we determine that a forecasted transaction is no longer probable of occurring, we discontinue hedge accounting for the affected portion of the hedge instrument, and any related unrealized gain or loss on the contract is recognized in current earnings.

Translation of Foreign Currencies

The functional currency for most of our foreign subsidiaries is their local currency. For the Company’s non-U.S. subsidiaries that transact in functional currency other than the U.S. dollar, assets and liabilities are translated at current rates of exchange at the balance sheet date. Income and expense items are translated at the average foreign exchange rates for the period. Adjustments resulting from the translation of the financial statements of our foreign operations into U.S. dollars are excluded from the determination of net income and are recorded in accumulated other comprehensive income, a separate component of equity. For subsidiaries where the functional currency differs from the local currency, non-monetary assets and liabilities are translated at the rate of exchange in effect on the date assets were acquired while monetary assets and liabilities are translated at current rates of exchange as of the balance sheet date. Income and expense items are translated at the average foreign currency rates for the period. Translation adjustments of these subsidiaries are included in net income.

Accounting for Share-Based Compensation

Our share-based compensation programs grant awards which have included stock options, restricted stock units which vest based on stock performance known as market stock units (MSUs), performance-vested restricted stock units which will be settled in cash (CSPSs), performance-vested restricted stock units which settle in shares (PVRSUs), time-vested restricted stock units (RSUs) and shares issued under our employee stock purchase plan (ESPP). We charge the estimated fair value of awards against income over the requisite service period, which is generally the vesting period. Where awards are made with non-substantive vesting periods (for instance, where a portion of the award vests upon retirement eligibility), we estimate and recognize expense based on the period from the grant date to the date on which the employee is retirement eligible.

The fair values of our stock option grants are estimated as of the date of grant using a Black-Scholes option valuation model and reflect estimated forfeitures. The estimated fair values of the stock options are then expensed over the options’ vesting periods.

The fair values of our RSUs are based on the market value of our stock on the date of grant. Compensation expense for RSUs is recognized over the applicable service period, adjusted for the effect of estimated forfeitures.

We apply an accelerated attribution method to recognize stock based compensation expense, net of estimated forfeitures, when accounting for our MSUs. The probability of actual shares expected to be earned is considered in the grant date valuation, therefore the expense will not be adjusted to reflect the actual units earned.

We apply an accelerated attribution method to recognize stock based compensation expense when accounting for our CSPSs and the fair value of the liability is remeasured at the end of each reporting period through expected cash settlement. Compensation expense associated with CSPSs is based upon the stock price and the number of units expected to be earned after assessing the probability that certain performance criteria will be met and the associated targeted payout level that is forecasted will be achieved, net of estimated forfeitures. Cumulative adjustments are recorded each quarter to reflect changes in the stock price and estimated outcome of the performance-related conditions until the date results are determined and settled.

We apply an accelerated attribution method to recognize stock based compensation expense when accounting for our PVRSUs. The number of units reflected as granted represents the target number of shares that are eligible to vest in full or in part and are earned subject to the attainment of certain performance criteria established at the beginning of the performance period. Compensation expense associated with these units is initially based upon the number of shares expected to vest after assessing the probability that certain performance criteria will be met and the associated targeted payout level that is forecasted will be achieved, net of estimated forfeitures. Cumulative adjustments are recorded quarterly to reflect subsequent changes in the estimated outcome of performance-related conditions until the date results are determined.

The purchase price of common stock under our ESPP is equal to 85% of the lower of (i) the market value per share of the common stock on the participant’s entry date into an offering period or (ii) the market value per share of the common stock on the purchase date. However, for each participant whose entry date is other than the start date of the offering period, the amount shall in no event be less than the market value per share of the common stock as of the beginning of the related offering period. The fair value of the discounted purchases made under our ESPP is calculated using the Black-Scholes model. The fair value of the look-back provision plus the 15% discount is recognized as compensation expense over the purchase period. We apply a graded vesting approach since our ESPP provides for multiple purchase periods and is, in substance, a series of linked awards.

Research and Development Expenses

Research and development expenses consist of upfront fees and milestones paid to collaborators and expenses incurred in performing research and development activities, including compensation and benefits, facilities expenses, overhead expenses, clinical trial and related clinical manufacturing expenses, fees paid to clinical research organizations (CROs) and other outside expenses. Research and development expenses are expensed as incurred. Payments we make for research and development services prior to the services being rendered are recorded as prepaid assets on our consolidated balance sheets and are expensed as the services are provided.

From time to time, we enter into development agreements in which we share expenses with a collaborative partner. We record payments received from our collaborative partners for their share of the development costs as a reduction of research and development expense, except as discussed within Note 19, Collaborations to these consolidated financial statements. Expenses incurred by Genentech in the development of RITUXAN are not recorded as research and development expense, but rather reduce our share of co-promotion profits recorded as a component of unconsolidated joint business revenue.

Income Taxes

The provision for income taxes includes federal, state, local and foreign taxes. Income taxes are accounted for under the liability method. Deferred tax assets and liabilities are recognized for the estimated future tax consequences of temporary differences between the financial statement carrying amounts and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates expected to apply to taxable income in the year in which the temporary differences are expected to be recovered or settled. We evaluate the realizability of our deferred tax assets and establish a valuation allowance when it is more likely than not that all or a portion of deferred tax assets will not be realized.

We account for uncertain tax positions using a “more-likely-than-not” threshold for recognizing and resolving uncertain tax positions. We evaluate uncertain tax positions on a quarterly basis and consider various factors, including, but not limited to, changes in tax law, the measurement of tax positions taken or expected to be taken in tax returns, the effective settlement of matters subject to audit, new audit activity and changes in facts or circumstances related to a tax position. We also accrue for potential interest and penalties, related to unrecognized tax benefits in income tax expense.

Contingencies

We are currently involved in various claims and legal proceedings. On a quarterly basis, we review the status of each significant matter and assess its potential financial exposure. If the potential loss from any claim, asserted or unasserted, or legal proceeding is considered probable and the amount can be reasonably estimated, we accrue a liability for the estimated loss. Significant judgment is required in both the determination of probability and the determination as to whether an exposure is reasonably estimable. Because of uncertainties related to these matters, accruals are based only on the best information available at the time. As additional information becomes available, we reassess the potential liability related to pending claims and litigation and may revise our estimates. These revisions in the estimates of the potential liabilities could have a material impact on our consolidated results of operations and financial position.

Restructuring Charges

We have made estimates and judgments regarding the amount and timing of our restructuring expense and liability, including current and future period termination benefits and other exit costs to be incurred when related actions take place. We have also assessed the recoverability of certain long-lived assets employed in the business and, in certain instances shortened the expected useful life of the assets based on changes in their expected use. When we determine that the useful lives of assets are shorter than we had originally estimated, we record additional depreciation to reflect the assets’ new shorter useful lives. Severance and other related costs and asset-related charges are reflected within our consolidated statement of income as a component of total restructuring charges incurred. Actual results may differ from these estimates. For a more detailed description of our recent restructuring efforts, please read Note 3, Restructuring, to these consolidated financial statements.

Earnings per Share

Basic earnings per share is computed using the two-class method. Under the two-class method, undistributed net income is allocated to common stock and participating securities based on their respective rights to share in dividends. We have determined that our preferred shares meet the definition of participating securities, and have allocated a portion of net income to our preferred shares on a pro rata basis. Net income allocated to preferred shares is excluded from the calculation of basic earnings per share. For basic earnings per share, net income available to holders of common stock is divided by the weighted average number of shares of common stock outstanding. For purposes of calculating diluted earnings per share, net income is adjusted for the after-tax amount of net income allocable to preferred shares, and the denominator includes both the weighted average number of shares of common stock outstanding and potential dilutive shares of common stock from stock options, unvested restricted stock awards, restricted stock units and other convertible securities, to the extent they are dilutive.

New Accounting Pronouncements

In April 2010, the FASB issued ASU No. 2010-17, Revenue Recognition — Milestone Method (ASU 2010-017). ASU 2010-017 provides guidance in applying the milestone method of revenue recognition to research or development arrangements. Under this guidance management may recognize revenue contingent upon the achievement of a milestone in its entirety, in the period in which the milestone is achieved, only if the milestone meets all the criteria within the guidance to be considered substantive. This ASU is effective on a prospective basis for research and development milestones achieved in fiscal years, beginning on or after June 15, 2010, which for Biogen Idec means fiscal 2011. Early adoption is permitted; however, we have elected to implement ASU 2010-17 prospectively, and as a result, the effect of this guidance will be limited to future transactions. We do not expect adoption of this standard to have a material impact on our financial position or results of operations as we have no material research and development arrangements which will be accounted for under the milestone method.

In December 2010, the FASB issued ASU No. 2010-027, Fees Paid to the Federal Government by Pharmaceutical Manufacturers (ASU 2010-027). ASU 2010-027 provides guidance concerning the recognition and classification of the new annual fee payable by branded prescription drug manufactures and importers on branded prescription drugs which was mandated under the health care reform legislation enacted in the U.S. in March 2010. Under this new accounting standard, the annual fee would be presented as a component of operating expenses and recognized over the calendar year such fees are payable using a straight-line method of allocation unless another method better allocates the fee over the calendar year. This ASU is effective for calendar years beginning on or after December 31, 2010, when the fee initially becomes effective, which for Biogen Idec is fiscal 2011. As this standard relates only to classification, the adoption of this accounting standard will not have an impact on our financial position or results of operations.

Acquisitions

12 Months Ended

Dec. 31, 2010

Acquisitions [Abstract]

Acquisitions


2.	Acquisitions

Acquisition of Panima Pharmaceuticals AG

On December 17, 2010, we completed our acquisition of 100% of the stock of Panima Pharmaceuticals AG (Panima), an affiliate of Neurimmune AG. The purchase price is comprised of a $32.5 million cash payment, plus contingent consideration in the form of development milestones up to $395.0 million in cash. Panima is a business involved in the discovery of antibodies designed to treat neurological disorders. The acquisition was funded from our existing cash on hand and has been accounted for as the acquisition of a business. In addition to acquiring 100% of the stock of the entity and obtaining the rights to three antibodies, we have obtained the services of key employees focused on these activities and acquired certain tangible fixed assets. Panima has also entered into an operating lease for lab and office space as well as a related contract services agreement with Neurimmune AG for the development of the acquired antibodies.

As of the acquisition date, we have recorded a liability of $81.2 million respresenting the fair value of the contingent consideration. This amount was estimated through a valuation model that incorporated industry based probability weighted assumptions related to the achievement of these milestones and thus the likelihood of us making payments. These cash outflow projections have been discounted using a rate of 6.1%, which is the cost of debt financing for market participants. This fair value measurement is based on significant inputs not observable in the market and therefore represents a Level 3 measurement.

The purchase price consists of the following:


(In millions)


Cash portion of consideration	$	32.5
Contingent consideration	$	81.2

Total purchase price	$	113.7

We have allocated the purchase price to the following separately identifiable assets and liabilities assumed as of December 17, 2010:


(In millions)


In process research and development	$	110.9
Goodwill		25.6
Deferred tax liability		(23.7	)
Other, net		0.9

Total purchase price	$	113.7

The goodwill recognized is largely attributable to establishing a deferred tax liability for the acquired IPR&D intangible asset, which is not deductible for income tax purposes.

The amount allocated to acquired IPR&D represents the fair value of such IPR&D programs, which were determined based on comparable transactions and a risk-adjusted estimate of cash flows utilizing a discount rate of 17.5%. One program is expected to be completed in 2019 at a cost of approximately $391.0 million and the other two programs are expected to be completed beginning in 2021 at a cost of approximately $788.0 million. This fair value measurement is based on significant inputs not observable in the market and thus represents a Level 3 fair value measurement.

Our results of operations include the results of Panima following the acquisition date. Separate pro forma financial information has not been provided as pro forma amounts approximate amounts reported for 2010.

In 2007, we entered into a collaboration agreement with Neurimmune SubOne AG, a subsidiary of Neurimmune AG, for the development and commercialization of antibodies for the treatment of Alzheimer’s disease. For a more detailed description of our collaboration agreement with Neurimmune, please read Note 18, Variable Interest Entities to these consolidated financial statements.

Acquisition of Biogen Idec Hemophilia Inc.

In connection with our acquisition of Biogen Idec Hemophilia Inc. (BIH), formerly Syntonix Pharmaceuticals, Inc. (Syntonix), in January 2007, we agreed to make additional future consideration payments based upon the achievement of certain milestone events associated with the development of BIH’s lead product, long-lasting recombinant Factor IX, a product for the treatment of hemophilia B. One of these milestones was achieved when, in January 2010, we initiated patient enrollment in a registrational trial of Factor IX. As a result of the achievement of this milestone, we paid approximately $40.0 million to the former shareholders of Syntonix. We recorded this payment as a charge to acquired in process research and development within our consolidated statements of income in accordance with the accounting standard applicable to business combinations when we acquired BIH.

Restructuring

12 Months Ended

Dec. 31, 2010

Restructuring [Abstract]

Restructuring


3.	Restructuring

On November 3, 2010, we announced a number of strategic, operational and organizational initiatives designed to provide a framework for the future growth of our business, which are summarized as follows:


	•	We intend to focus our business on neurology and leverage our strengths in biologics research, development and manufacturing to pursue select biological therapies where there is a significant unmet need and where the drug candidate has the potential to be highly differentiated. Accordingly, during the fourth quarter of 2010, we began to reallocate resources within our research and development organization to maximize our investment in our highest-potential programs. As a result, we have terminated or are in the process of discontinuing certain research and development programs, including substantially all of our oncology programs (which we are looking to spin out or out-license), our cardiovascular programs and select neurology and immunology programs. In addition, we have substantially reduced our small molecule discovery activities in favor of outsourcing these efforts.

	•	We are in the process of vacating the San Diego, California facility and consolidating our Massachusetts facilities. In October 2010, we sold the San Diego facility and agreed to lease back the facility for a period of 15 months. For a more detailed description of these transactions, please read Note 10, Property, Plant and Equipment to these consolidated financial statements.

	•	We eliminated our RITUXAN oncology and rheumatology sales force and Genentech, Inc., a wholly-owned member of the Roche Group, has assumed sole responsibility for the U.S. sales and marketing efforts related to RITUXAN.

	•	We are in the process of completing a 13% reduction in workforce and realigning our overall structure to become a more efficient and cost-effective organization. The workforce reduction spans our sales, research and development and administrative functions.

We expect to incur total restructuring charges of approximately $110.0 million, comprised of approximately $90.0 million for workforce reduction and $20.0 million for facility consolidation.

We recognized $75.2 million of these charges within our consolidated statement of income during 2010, which are summarized as follows:


	For the Year Ended
(In millions)	December 31, 2010

Workforce reduction	$	67.2
Facility consolidation		8.0

Total restructuring charges	$	75.2

We expect that our restructuring effort will be substantially completed, and that substantially all of the remaining restructuring charges will be incurred by the end of 2011.

Costs associated with our workforce reduction primarily relate to employee severance and benefits. Facility consolidation costs are primarily comprised of charges associated with the closing of facilities, related lease obligations and additional depreciation recognized when the expected useful lives of certain assets have been shortened due to the consolidation and closing of related facilities and the discontinuation of certain research and development programs.

The following table summarizes the charges and spending related to our restructuring efforts during 2010:


	Workforce			Facility
(In millions)	Reduction			Consolidation			Total

Reserves established	$	67.2		$	8.0		$	75.2
Amounts paid		(6.6	)		—			(6.6	)
Additional depreciation and other non-cash charges		—			(2.2	)		(2.2	)

Restructuring reserves at December 31, 2010	$	60.6		$	5.8		$	66.4

We expect that substantially all remaining payments will be made, by the end of 2011.

Revenue Reserves

12 Months Ended

Dec. 31, 2010

Revenue Reserves [Abstract]

Revenue Reserves


4.	Revenue Reserves

Reserves for Discounts and Allowances

An analysis of the amount of, and change in, reserves is summarized as follows:


				Contractual
(In millions)	Discounts			Adjustments			Returns			Total

2010
Beginning balance	$	13.9		$	70.3		$	18.9		$	103.1
Current provisions relating to sales in current year		80.6			285.0			16.1			381.7
Adjustments relating to prior years		(2.7	)		(2.4	)		(1.8	)		(6.9	)
Payments/returns relating to sales in current year		(68.7	)		(184.3	)		(0.8	)		(253.8	)
Payments/returns relating to sales in prior years		(9.2	)		(61.6	)		(11.3	)		(82.1	)

Ending balance	$	13.9		$	107.0		$	21.1		$	142.0


				Contractual
(In millions)	Discounts			Adjustments			Returns			Total

2009
Beginning balance	$	9.2		$	48.1		$	18.1		$	75.4
Current provisions relating to sales in current year		74.0			192.5			15.8			282.3
Adjustments relating to prior years		—			—			0.8			0.8
Payments/returns relating to sales in current year		(60.8	)		(124.4	)		(0.6	)		(185.8	)
Payments/returns relating to sales in prior years		(8.5	)		(45.9	)		(15.2	)		(69.6	)

Ending balance	$	13.9		$	70.3		$	18.9		$	103.1


				Contractual
(In millions)	Discounts			Adjustments			Returns			Total

2008
Beginning balance	$	6.4		$	33.1		$	20.4		$	59.9
Current provisions relating to sales in current year		67.1			150.6			14.7			232.4
Adjustments relating to prior years		—			(1.6	)		(2.5	)		(4.1	)
Payments/returns relating to sales in current year		(57.8	)		(101.2	)		(0.1	)		(159.1	)
Payments/returns relating to sales in prior years		(6.5	)		(32.8	)		(14.4	)		(53.7	)

Ending balance	$	9.2		$	48.1		$	18.1		$	75.4

The total reserves above, included in our consolidated balance sheets, are summarized as follows:


	As of December 31,
(In millions)	2010		2009

Reduction of accounts receivable	$	36.7	$	43.3
Current liability		105.3		59.8

Total reserves	$	142.0	$	103.1

Healthcare Reform

In 2010, healthcare reform legislation was enacted in the U.S. This legislation contains several provisions that affected our business and our accounting estimates. Although many provisions of the new legislation do not take effect immediately, several provisions became effective in 2010. These include (1) an increase in the minimum Medicaid rebate to states participating in the Medicaid program from 15.1% to 23.1% on our branded prescription drugs; (2) the extension of the Medicaid rebate to Managed Care Organizations that dispense drugs to Medicaid beneficiaries; and (3) the expansion of the 340(B) PHS drug pricing program, which provides outpatient drugs at reduced rates, to include additional hospitals, clinics, and healthcare centers. These incremental discounts have been factored into determining the amount and timing of our revenues on sales to certain customers and are based upon several assumptions about the implementation of this new legislation. Our estimates are based upon our knowledge of current events and actual results may ultimately differ from these estimates.

Inventory

12 Months Ended

Dec. 31, 2010

Inventory [Abstract]

Inventory


5.	Inventory

The components of inventory are summarized as follows:


	As of December 31,
(In millions)	2010		2009

Raw materials	$	59.0	$	49.2
Work in process		142.2		174.0
Finished goods		87.9		70.8

Total inventory	$	289.1	$	294.0

The components of inventory by product are summarized as follows:


	As of December 31,
(In millions)	2010		2009

AVONEX	$	87.0	$	76.8
TYSABRI		117.0		144.0
Other		26.1		24.0

Total finished goods and work in process	$	230.1	$	244.8

Raw materials		59.0		49.2

Total inventory	$	289.1	$	294.0

Amounts written-down down related to unmarketable inventory were as follows:


	For the Years Ended
	December 31,
(In millions)	2010		2009		2008

Write-downs of unmarketable inventory	$	11.8	$	16.9	$	29.8

Intangible Assets and Goodwill

12 Months Ended

Dec. 31, 2010

Intangible Assets and Goodwill [Abstract]

Intangible Assets and Goodwill


6.	Intangible Assets and Goodwill

In December 2010, we completed our acquisition of Panima and allocated a portion of the total purchase price as follows: $110.9 million to IPR&D and $25.6 million to goodwill. For a more detailed description of this transaction, please read Note 2, Acquisitions to these consolidated financial statements.

Intangible Assets

Intangible assets, net of accumulated amortization, impairment charges and adjustments, are summarized as follows:


		As of December 31, 2010							As of December 31, 2009
	Estimated			Accumulated							Accumulated
(In millions)	Life	Cost		Amortization			Net		Cost		Amortization			Net

Intangible assets:
Out-licensed patents	12 years	$	578.0	$	(350.2	)	$	227.8	$	578.0	$	(306.0	)	$	272.0
Core developed technology	15-23 years		3,005.3		(1,636.9	)		1,368.4		3,005.3		(1,472.4	)		1,532.9
In process research and development	up to 15 years upon commercialization		110.9		—			110.9		—		—			—
Trademarks and tradenames	Indefinite		64.0		—			64.0		64.0		—			64.0
In-licensed patents	14 years		3.0		(1.3	)		1.7		3.0		(1.1	)		1.9
Assembled workforce	4 years		2.1		(2.1	)		—		2.1		(1.8	)		0.3
Distribution rights	2 years		12.7		(12.7	)		—		12.7		(12.7	)		—

Total intangible assets		$	3,776.0	$	(2,003.2	)	$	1,772.8	$	3,665.1	$	(1,794.0	)	$	1,871.1

Other than the amounts recorded in connection with our acquisition of Panima, intangible assets were unchanged as of December 31, 2010, as compared to December 31, 2009, exclusive of the impact of amortization. Our most significant intangible asset is the core technology related to our AVONEX product. The net book value of this asset as of December 31, 2010 and 2009 was $1,354.3 million and $1,516.7 million, respectively.

Amortization of acquired intangible assets totaled $208.9 million, $289.8 million and $332.7 million for the years ended December 31, 2010, 2009 and 2008, respectively. Based upon our most recent analysis, amortization of intangible assets included within our consolidated balance sheet as of December 31, 2010, is expected to be in the range of approximately $170.0 million to $210.0 million annually through 2015.

Goodwill

The following table provides a roll forward of the changes in goodwill:


	As of December 31,
(In millions)	2010			2009

Goodwill:
Beginning balance	$	1,138.6		$	1,138.6
Goodwill acquired during the year		25.6			—
Other		(17.9	)		—

Ending balance	$	1,146.3		$	1,138.6

During 2010, we recorded a decrease to goodwill of $17.9 million to establish a deferred tax asset that existed at the time of the merger of Biogen, Inc and IDEC Pharmaceuticals Corporation in 2003.

Fair Value Measurements

12 Months Ended

Dec. 31, 2010

Fair Value Measurements [Abstract]

Fair Value Measurements


7.	Fair Value Measurements

A majority of our financial assets and liabilities have been classified as Level 2. Our financial assets and liabilities (which include our cash equivalents, derivative contracts, marketable debt securities, and plan assets for deferred compensation) have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, typically utilizing third party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches and observable market inputs to determine value. These observable market inputs include reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates and other industry and economic events.

We validate the prices provided by our third party pricing services by reviewing their pricing methods and matrices, obtaining market values from other pricing sources, analyzing pricing data in certain instances and confirming that the relevant markets are active. After completing our validation procedures, we did not adjust or override any fair value measurements provided by our pricing services as of December 31, 2010 and December 31, 2009.

Our strategic investments in publicly traded equity securities are classified as Level 1 assets as their fair values are readily determinable and based on quoted market prices.

We also maintain certain investments classified as Level 3 whose fair value is initially measured at transaction prices and subsequently valued using the pricing of recent financing or by reviewing the underlying economic fundamentals and liquidation value of the companies. Our venture capital investments are the only investments for which we used Level 3 inputs to determine the fair value and represented approximately 0.3% of our total assets as of both December 31, 2010 and December 31, 2009. These investments include investments in certain biotechnology oriented venture capital funds which primarily invest in small privately-owned, venture-backed biotechnology companies. The fair value of our investments in these venture capital funds has been estimated using the net asset value of the fund. The investments cannot be redeemed within the funds. Distributions from each fund will be received as the underlying investments of the fund are liquidated. The funds and therefore a majority of the underlying assets of the funds will not be liquidated in the near future. The underlying assets in these funds are initially measured at transaction prices and subsequently valued using the pricing of recent financings or by reviewing the underlying economic fundamentals and liquidation value of the companies that the funds invest in. We apply judgments and estimates when we validate the prices provided by third parties. While we believe the valuation methodologies are appropriate, the use of valuation methodologies is highly judgmental and changes in methodologies can have a material impact on our results of operations. Gains and losses (realized and unrealized) included in earnings for the period are reported in other income (expense), net.

The tables below present information about our assets and liabilities that are measured at fair value on a recurring basis as of December 31, 2010 and December 31, 2009, and indicate the fair value hierarchy of the valuation techniques we utilized to determine such fair value:


			Quoted		Significant
			Prices		Other		Significant
	As of		in Active		Observable		Unobservable
	December 31,		Markets		Inputs		Inputs
(In millions)	2010		(Level 1)		(Level 2)		(Level 3)

Assets:
Cash equivalents	$	651.8	$	—	$	651.8	$	—
Marketable debt securities:
Corporate debt securities		313.0		—		313.0		—
Government securities		785.3		—		785.3		—
Mortgage and other asset backed securities		92.9		—		92.9		—
Strategic investments		44.8		44.8		—		—
Venture capital investments		20.8		—		—		20.8
Derivative contracts		1.3		—		1.3		—
Plan assets for deferred compensation		13.0		—		13.0		—

Total	$	1,922.9	$	44.8	$	1,857.3	$	20.8

Liabilities:
Derivative contracts	$	12.2	$	—	$	12.2	$	—
Contingent consideration (Note 2)		81.2		—		—		81.2

Total	$	93.4	$	—	$	12.2	$	81.2


			Quoted		Significant
			Prices		Other		Significant
	As of		in Active		Observable		Unobservable
	December 31,		Markets		Inputs		Inputs
(In millions)	2009		(Level 1)		(Level 2)		(Level 3)

Assets:
Cash equivalents	$	476.4	$	—	$	476.4	$	—
Marketable debt securities:
Corporate debt securities		504.1		—		504.1		—
Government securities		1,133.5		—		1,133.5		—
Mortgage and other asset backed securities		238.3		—		238.3		—
Strategic investments		5.9		5.9		—		—
Venture capital investments		21.9		—		—		21.9
Derivative contracts		15.8		—		15.8		—
Plan assets for deferred compensation		13.6		—		13.6		—

Total	$	2,409.5	$	5.9	$	2,381.7	$	21.9

Liabilities:
Derivative contracts		11.1		—		11.1		—

Total	$	11.1	$	—	$	11.1	$	—

In addition to the assets and liabilities measured at fair value on a recurring basis, as included with the tables above, during the fourth quarter of 2010 we recognized a Level 3 asset related to IPR&D as well as a Level 3 contingent consideration liability upon our acquisition of Panima on December 17, 2010. There has been no significant change in the valuation of this liability from the acquisition date through December 31, 2010. For a more detailed discussion of our valuation of this asset, please read Note 2, Acquisitions to these consolidated financial statements.

The following table provides a roll forward of the fair value of our venture capital investments, which are all Level 3 assets:


	As of December 31,
(In millions)	2010			2009

Beginning balance	$	21.9		$	23.9
Total net unrealized gains (losses) included in earnings		(2.1	)		(3.6	)
Net purchases, issuances, and settlements		1.0			1.6

Ending balance	$	20.8		$	21.9

The fair values of our debt instruments, which are all Level 2 liabilities, are summarized as follows:


	As of December 31,
(In millions)	2010		2009

Credit line from Dompé	$	8.1	$	17.2
Notes payable to Fumedica		24.2		31.3
6.0% Senior Notes due 2013		485.5		475.7
6.875% Senior Notes due 2018		618.0		589.1

Total fair value	$	1,135.8	$	1,113.3

The fair values of our credit line from Dompé and our note payable to Fumedica were estimated using market observable inputs. The fair value of our Senior Notes was determined through market, observable and corroborated sources.

Financial Instruments

12 Months Ended

Dec. 31, 2010

Financial Instruments [Abstract]

Financial Instruments


8.	Financial Instruments

Marketable Securities, including Strategic Investments

The following tables summarize our marketable securities and strategic investments:


			Gross		Gross
	Fair		Unrealized		Unrealized			Amortized
As of December 31, 2010 (In millions):	Value		Gains		Losses			Cost

Available-for-sale
Corporate debt securities
Current	$	93.2	$	0.1	$	—		$	93.1
Non-current		219.8		2.1		(0.5	)		218.2
Government securities
Current		352.8		0.2		—			352.6
Non-current		432.5		0.6		(0.6	)		432.5
Mortgage and other asset backed securities
Current		2.1		—		—			2.1
Non-current		90.8		0.5		(0.2	)		90.5

Total available-for-sale securities	$	1,191.2	$	3.5	$	(1.3	)	$	1,189.0

Other Investments
Strategic investments, non-current	$	44.8	$	17.5	$	—		$	27.3


			Gross		Gross
	Fair		Unrealized		Unrealized			Amortized
As of December 31, 2009 (In millions):	Value		Gains		Losses			Cost

Available-for-sale
Corporate debt securities
Current	$	177.2	$	1.5	$	—		$	175.7
Non-current		326.9		5.7		(0.3	)		321.5
Government securities
Current		501.6		1.2		—			500.4
Non-current		631.9		4.1		(0.5	)		628.3
Mortgage and other asset backed securities
Current		3.0		0.1		—			2.9
Non-current		235.3		4.1		(0.5	)		231.7

Total available-for-sale securities	$	1,875.9	$	16.7	$	(1.3	)	$	1,860.5

Other Investments
Strategic investments, non-current	$	5.9	$	2.7	$	(0.3	)	$	3.5

In the tables above, as of December 31, 2010 and 2009, government securities included $163.5 million and $298.8 million, respectively, of Federal Deposit Insurance Corporation (FDIC) guaranteed senior notes issued by financial institutions under the Temporary Liquidity Guarantee Programs.

Certain commercial paper and short-term debt securities with original maturities of less than 90 days are included in cash and cash equivalents on the accompanying consolidated balance sheets and are not included in the tables above. As of December 31, 2010 and 2009, such commercial paper and CDs, including accrued interest, had fair and carrying values of $30.0 million and $76.9 million, respectively, and short-term debt securities had fair and carrying values of $621.8 million and $399.5 million, respectively.

Summary of Contractual Maturities: Available-for-Sale Securities

The estimated fair value and amortized cost of our marketable securities, excluding strategic investments, available-for-sale by contractual maturity are summarized as follows:


	As of December 31, 2010				As of December 31, 2009
	Estimated		Amortized		Estimated		Amortized
(In millions)	Fair Value		Cost		Fair Value		Cost

Due in one year or less	$	448.1	$	447.8	$	522.0	$	519.5
Due after one year through five years		664.1		662.4		1,143.7		1,133.4
Due after five years		79.0		78.8		210.2		207.6

Total available-for-sale securities	$	1,191.2	$	1,189.0	$	1,875.9	$	1,860.5

The average maturity of our marketable securities as of December 31, 2010 and 2009 was 11 months and 15 months, respectively.

Proceeds from Maturities and Sales of Marketable Securities, excluding Strategic Investments

The proceeds from maturities and sales of marketable securities, excluding strategic investments, and resulting realized gains and losses, are summarized as follows:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Proceeds from maturities and sales	$	2,668.7	$	3,319.0	$	2,941.1
Realized gains	$	18.8	$	19.8	$	15.9
Realized losses	$	2.5	$	4.0	$	17.0

Proceeds were generally reinvested. Realized losses for the year ended December 31, 2010, primarily relate to the sale of agency mortgage-backed securities and corporate debt securities. Realized losses for the year ended December 31, 2009 and 2008, primarily relate to losses on the sale of non-agency mortgage-backed securities and corporate debt securities.

Strategic Investments

In 2010, we sold one strategic investment for $1.8 million, which resulted in an insignificant loss. In 2009 we sold two strategic investments for $5.9 million, which resulted in a $3.0 million gain. In 2008, we did not sell any portion of our strategic investments. Strategic investments are included in investments and other assets on the accompanying consolidated balance sheets.

In addition to the strategic investments and venture capital investments noted in Note 7, Fair Value Measurements to these consolidated financial statements, we hold other investments in equity securities of certain privately-owned biotechnology companies and biotechnology oriented venture capital funds accounted for using the cost method. The cost basis of these securities as of December 31, 2010 and 2009 is $35.0 million and $73.9 million, respectively. These securities are also included in investments and other assets on the accompanying consolidated balance sheets.

Impairments

Prior to the adoption of new accounting standards for the recognition, measurement and presentation of other-than-temporary impairments in April 2009, we recognized all other-than-temporary impairment amounts related to our marketable debt securities in earnings as required under the previously effective guidance which required that management assert that it had the ability and intent to hold a debt security until maturity or until we recovered the cost of our investment.

In 2010, 2009 and 2008, we recognized $16.6 million, $3.8 million, and $16.3 million, in charges, respectively, for the impairment of publicly-held strategic investments and for declines in value of funds that were determined to be other-than-temporary.

In 2010, 2009 and 2008, we recorded $4.1 million, $3.2 million, and $2.3 million, respectively, in charges for the impairment for certain investments in privately-held companies and declines in value of funds recorded under the cost method that were determined to be other-than-temporary.

In 2009, we recognized $3.6 million in charges for the other-than-temporary impairment on marketable debt securities. For 2008, we recognized $41.7 million in charges for the other-than-temporary impairment of marketable debt securities primarily related to mortgage and asset-backed securities.

Derivative Instruments

12 Months Ended

Dec. 31, 2010

Derivative Instruments [Abstract]

Derivative Instruments


9.	Derivative Instruments

Foreign Currency Forward Contracts

Due to the global nature of our operations, portions of our revenues are in currencies other than the U.S. dollar. The value of revenues measured in U.S. dollars is therefore subject to changes in currency exchange rates. In order to mitigate the impact of fluctuations in currency exchange rates we use foreign currency forward contracts to lock-in the foreign exchange rates associated with a portion of our forecasted international revenues.

Foreign currency forward contracts in effect as of December 31, 2010 and 2009 had durations of 1 to 12 months. These contracts have been designated as cash flow hedges and accordingly, to the extent effective, any unrealized gains or losses on these foreign currency forward contracts are reported in accumulated other comprehensive income (loss). Realized gains and losses for the effective portion of such contracts are recognized in revenue when the sale of product in the currency being hedged is recognized. To the extent ineffective, hedge transaction gains and losses are reported in other income (expense), net.

The notional value of foreign currency forward contracts that were entered into to hedge forecasted revenue is summarized as follows:


	Notional Amount
	As of December 31,
Foreign Currency: (In millions)	2010		2009

Euro	$	460.3	$	495.9
Canadian dollar		24.0		22.3
Swedish krona		9.9		—

Total foreign currency forward contracts	$	494.2	$	518.2

The portion of the fair value of these contracts that was included in accumulated other comprehensive income (loss) within total equity reflected losses of $11.0 million and gains of $1.2 million as of December 31, 2010 and 2009, respectively. We expect all contracts to be settled over the next 12 months and any amounts in accumulated other comprehensive income (loss) to be reported as an adjustment to revenue. We consider the impact of our and our counterparties’ credit risk on the fair value of the contracts as well as the ability of each party to execute its obligations under the contract. As of December 31, 2010 and 2009, respectively, credit risk did not materially change the fair value of our foreign currency forward contracts.

In relation to our foreign currency forward contracts, we recognized in other income (expense) net gains of $0.4 million and net losses of $1.1 million and $0.2 million for the years ended December 31, 2010, 2009 and 2008, respectively, due to hedge ineffectiveness.

In addition, for the year ended December 31, 2010, we recognized in product revenue $45.7 million of net gains compared to net losses of $49.7 million and $8.5 million, for the years ended December 31, 2009 and 2008, respectively, for the settlement of certain effective cash flow hedge instruments. These settlements were recorded in the same period as the related forecasted revenue.

Summary of Derivatives Designated as Hedging Instruments

The following table summarizes the fair value and presentation in the consolidated balance sheets for derivatives designated as hedging instruments:


		Fair Value
(In millions)	Balance Sheet Location	As of December 31, 2010

Foreign Currency Contracts
Asset derivatives	Other current assets	$	—
Liability derivatives	Accrued expenses and other	$	11.0


		Fair Value
(In millions)	Balance Sheet Location	As of December 31, 2009

Foreign Currency Contracts
Asset derivatives	Other current assets	$	10.8
Liability derivatives	Accrued expenses and other	$	9.8

The following table summarizes the effect of derivatives designated as hedging instruments on the consolidated statements of income:


	Amount					Amount
	Recognized in					Reclassified from
	Accumulated Other					Accumulated Other
	Comprehensive					Comprehensive
	Income (Loss)					Income (Loss)				Amount of
	on Derivative			Income Statement		into Income			Income Statement	Gain/(Loss)
	Gain/(Loss)			Location		Gain/(Loss)			Location	Recorded
For the Years Ended (In millions)	(Effective Portion)			(Effective Portion)		(Effective Portion)			(Ineffective Portion)	(Ineffective Portion)

December 31, 2010:
Foreign currency contracts	$	(11.0	)		Revenue	$	45.7		Other income (expense)	$	0.4
December 31, 2009:
Foreign currency contracts	$	1.2			Revenue	$	(49.7	)	Other income (expense)	$	(1.1	)
December 31, 2008:
Foreign currency contracts	$	(44.1	)		Revenue	$	(8.5	)	Other income (expense)	$	0.2
Interest rate swap	$	—			Interest expense	$	—		Interest expense	$	(8.9	)

Other Derivatives

We also enter into other foreign currency forward contracts, usually with one month durations, to mitigate the foreign currency risk related to certain balance sheet positions. We have not elected hedge accounting for these transactions. The aggregate notional amount of our outstanding foreign currency contracts was $160.8 million and $188.0 million as of December 31, 2010 and 2009, respectively. The fair value of these contracts was a net asset of $0.1 million as of December 31, 2010 compared to a net asset of $3.8 million as of December 31, 2009. Net gains of $6.0 million and $2.5 million related to these contracts were recognized as a component of other income (expense), net, for years ended December 31, 2010 and 2009, respectively.

Interest Rate Swaps

In connection with the issuance of our 6.875% Senior Notes in March 2008, we entered into interest rate swap contracts with an aggregate notional amount of $550.0 million. We terminated these interest rate swaps in December 2008 and received $53.9 million upon settlement. In the year ended December 31, 2008, we recognized a net loss of $8.9 million in earnings due to hedge ineffectiveness.

Upon termination of the interest rate swaps in December 2008, the carrying amount of the 6.875% Senior Notes increased $62.8 million. This amount will be recognized as a reduction of interest expense and amortized using the effective interest rate method over the remaining life of the 6.875% Senior Notes. In 2010 and 2009, approximately $5.7 million and $5.4 million, respectively, was recorded as a reduction of interest expense.

Property, Plant and Equipment

12 Months Ended

Dec. 31, 2010

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment


10.	Property, Plant and Equipment

Property, plant and equipment are recorded at historical cost, net of accumulated depreciation. Components of property, plant and equipment, net are summarized as follows:


	As of December 31,
(In millions)	2010			2009

Land	$	107.6		$	111.2
Buildings		670.2			669.7
Leasehold improvements		100.8			73.1
Machinery and equipment		576.0			534.0
Computer software and hardware		392.8			334.2
Furniture and fixtures		54.5			50.7
Construction in progress		506.9			506.7

Total cost		2,408.8			2,279.6

Less: accumulated depreciation		(767.2	)		(642.5	)

Total property, plant and equipment, net	$	1,641.6		$	1,637.1

Depreciation expense was $144.9 million, $137.9 million, and $129.1 million for 2010, 2009, and 2008, respectively.

Hillerød, Denmark Facility

As of December 31, 2010 and 2009, the construction in progress balance related to the construction of our large-scale biologic manufacturing facility in Hillerød, Denmark totaled $440.2 million and $441.2 million, respectively. In connection with our construction of this facility, we capitalized approximately $28.4 million, $28.4 million and $23.2 million of interest costs to construction in progress for 2010, 2009 and 2008, respectively.

This facility is intended to manufacture large molecule products. Recent manufacturing improvements have resulted in favorable production yields on TYSABRI, that along with slower than expected TYSABRI growth, have reduced our expected capacity requirements. As a result, we plan to delay the start of manufacturing activities at this site until additional capacity is required by the business and stop further validation once operational qualification activities are completed in the first half of 2011.

San Diego Facility

On October 1, 2010, we sold the San Diego facility, which is comprised of 43 acres of land and buildings totaling approximately 355,000 square feet of laboratory and office space, for cash proceeds, net of transaction costs, of approximately $127.0 million. We had an option to cause the buyer to construct a 160,000 square foot office and laboratory facility in San Diego which we would lease for a term of 10 years, which was not exercised and expired on November 1, 2010. As part of this transaction, we have also agreed to lease back the San Diego facility for a period of 15 months. We are accounting for this transaction as a financing arrangement.

We have determined that the transaction does not qualify as a sale due to our continuing involvement under the leaseback terms. Accordingly, the facility assets remain classified as held for use and their carrying value is reflected as a component of property, plant and equipment, net within our consolidated balance sheet as of December 31, 2010. We have not recognized a loss or impairment charge related to the San Diego facility.

The net carrying amounts of the major classes of assets are summarized as follows:


	As of
	December 31,
(In millions)	2010

Land	$	45.7
Buildings		73.0
Furniture and fixtures		2.1
Machinery and equipment		5.6

Total cost	$	126.4

In January 2011, we entered into an agreement to terminate our 15 month lease of the San Diego facility. Under the terms of this agreement, we will continue to make monthly rental payments through August 31, 2011 and will have no continuing involvement or remaining obligation after that date. Once the lease arrangement has concluded we will account for the San Diego facility as a sale of property. We are scheduled to incur debt service payments and interest totaling approximately $6.9 million over the term of the revised leaseback period.

Other

In November 2010, we decided to close the facility in San Diego, California and consolidate our Massachusetts facilities. If we decide to further consolidate, co-locate or dispose of certain aspects of our business operations, for strategic or other operational reasons, we may dispose of one or more of our properties. If we determine that the fair value of any of our owned properties, including any properties we may classify as held for sale, is lower than their book value or we cannot recover the net book value of these assets, we may incur impairment charges which could be significant. In addition, if we decide to fully or partially vacate a leased property, we may incur significant cost, including lease termination fees, rent expense in excess of sublease income and impairment of leasehold improvements.

Indebtedness

12 Months Ended

Dec. 31, 2010

Indebtedness [Abstract]

Indebtedness


11.	Indebtedness

Our indebtedness is summarized as follows:


	As of December 31,
(In millions)	2010		2009

Current portion:
Note payable to Fumedica	$	3.3	$	11.2
Credit line from Dompé		8.0		8.6
Financing arrangement for the sale of the San Diego facility		125.9		—

Current portion of notes payable, line of credit and other financing arrangements	$	137.2	$	19.8

Non-current portion:
6.0% Senior notes due 2013	$	449.8	$	449.6
6.875% Senior notes due 2018		597.9		603.2
Note payable to Fumedica		18.7		18.8
Credit line from Dompé		—		8.6

Non-current portion of notes payable and line of credit	$	1,066.4	$	1,080.2

The following is a summary description of our principal indebtedness as of December 31, 2010:

Senior Notes

On March 4, 2008, we issued $450.0 million aggregate principal amount of 6.0% Senior Notes due March 1, 2013 and $550.0 million aggregate principal amount of 6.875% Senior Notes due March 1, 2018 at 99.886% and 99.184% of par, respectively. The discount is amortized as additional interest expense over the period from issuance through maturity. These notes are senior unsecured obligations. Interest on the notes is payable March 1 and September 1 of each year. The notes may be redeemed at our option at any time at 100% of the principal amount plus accrued interest and a specified make-whole amount. The notes contain a change of control provision that may require us to purchase the notes under certain circumstances. There is also an interest rate adjustment feature that requires us to pay interest at an increased interest rate on the notes if the credit rating on the notes declines below investment grade. Offering costs of approximately $8.0 million have been recorded as debt issuance costs on our consolidated balance sheet and are amortized as additional interest expense using the effective interest rate method over the period from issuance through maturity.

Upon the issuance of the debt we entered into interest rate swap contracts where we received a fixed rate and paid a variable rate, as further described in Note 9, Derivative Instruments to these consolidated financial statements. These contracts were terminated in December 2008. Upon termination of these swaps, the carrying amount of the 6.875% Senior Notes due in 2018 was increased by $62.8 million and is being amortized using the effective interest rate method over the remaining life of the Senior Notes and is being recognized as a reduction of interest expense. As of December 31, 2010, there is $51.4 million remaining to be amortized.

Revolving Credit Facility

We have a $360.0 million senior unsecured revolving credit facility, which may be used for future working capital and general corporate purposes. The facility terminates in June 2012. During 2010, 2009 and 2008 there were no borrowings under this credit facility and we were in compliance with all applicable covenants.

Biogen-Dompé

As of December 31, 2010 and 2009, Biogen-Dompé SRL, a consolidated joint venture, has a loan balance of 6.0 million Euros ($8.0 million) and 12.0 million Euros ($17.2 million), respectively. These balances represent a line of credit from us and Dompé Farmaceutici SpA, half of which has been eliminated for purposes of presenting our consolidated financial position as it is an intercompany loan. Borrowings under this line of credit are to be made equally between the partners, with any repayments paid in a similar manner. The interest rate on the line of credit is the three month Euro LIBOR plus 150 basis points and was 2.4% and 2.2% as of December 31, 2010 and 2009, respectively. The interest rate is reset quarterly and payable quarterly in arrears. Any borrowing on the line of credit is due, in full, on December 1, 2011.

Notes Payable to Fumedica

In connection with our 2006 distribution agreement with Fumedica, we issued notes totaling 61.4 million Swiss Francs which were payable to Fumedica in varying amounts from June 2008 through June 2018. In June 2010, we repaid 12.0 million Swiss Francs ($10.3 million) of the outstanding amount. As of December 31, 2010, our remaining note payable to Fumedica has a present value of 20.7 million Swiss Francs ($22.0 million) and remains payable in a series of payments through June 2018.

Financing Arrangement

As described in Note 10, Property, Plant & Equipment to these consolidated financial statements, on October 1, 2010, we sold the San Diego facility and agreed to lease back the facility for a period of 15 months. We have accounted for these transactions as a financing arrangement and recorded an obligation of $127.0 million on that date, reflecting cash proceeds received net of transaction costs. As of December 31, 2010, our remaining obligation was $125.9 million, which is reflected as a component of current portion of notes payable, line of credit and other financing arrangements within our consolidated balance sheet. In January 2011, we entered into an agreement to terminate our 15 month lease of the San Diego facility. Under the terms of this agreement, we will continue to make monthly rental payments through August 31, 2011 and will have no continuing involvement or remaining obligation after that date. Once the lease arrangement has concluded we will account for the San Diego facility as a sale of property. We are scheduled to incur debt service payments and interest totaling approximately $6.9 million over the term of the revised leaseback period.

Debt Maturity

Our total debt, excluding the San Diego financing arrangement, matures as follows:


(In millions)	As of December 31, 2010

2011	$	11.4
2012		3.4
2013		453.4
2014		3.4
2015		3.4
2016 and thereafter		560.2

Total	$	1,035.2

The fair value of our debt is disclosed in Note 7, Fair Value Measurements to these consolidated financial statements.

Equity

12 Months Ended

Dec. 31, 2010

Equity [Abstract]

Stockholders' Equity


12.	Equity

Preferred Stock

The following table describes the number of shares authorized, issued and outstanding of our preference stock as of December 31, 2010 and 2009:


	As of December 31, 2010						As of December 31, 2009
(In thousands)	Authorized		Issued		Outstanding		Authorized		Issued		Outstanding

Series A		1,750		8		8		1,750		8		8
Series X junior participating		1,000		—		—		1,000		—		—
Undesignated		5,250		—		—		5,250		—		—

Total preferred stock		8,000		8		8		8,000		8		8

We have 8,000,000 shares of Preferred Stock authorized, of which 1,750,000 shares have been designated as Series A Preferred Stock and 1,000,000 shares have been designated as Series X Junior Participating Preferred Stock. The shares may be issued without a vote or action of stockholders from time to time in classes or series with the designations, powers, preferences, and the relative, participating, optional or other special rights of the shares of each such class or series and any qualifications, limitations or restrictions thereon as set forth in the instruments governing such shares. Any such Preferred Stock may rank prior to common stock as to dividend rights, liquidation preference or both, and may have full or limited voting rights and may be convertible into shares of common stock. As of December 31, 2010, 2009 and 2008, there were 8,221 shares of Series A Preferred Stock issued and outstanding. These shares carry a liquidation preference of $67 per share and are convertible into 60 shares of common stock per share of Preferred Stock. No other shares of Preferred Stock are issued and outstanding as of December 31, 2010 and 2009.

Common Stock

The following table describes the number of shares authorized, issued and outstanding of our common stock as of December 31, 2010 and 2009:

As of December 31, 2010

As of December 31, 2009

(In thousands)

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Common stock

1,000,000

248,200

240,538

1,000,000

288,494

274,855

Share Repurchases

During 2010, we repurchased approximately 40.3 million shares of common stock at a cost of approximately $2.1 billion under our 2010 and 2009 share repurchase authorizations. We retired all of these shares as they were acquired. In connection with this retirement, in accordance with our policy, we recorded an approximately $2.1 billion reduction in additional paid-in-capital. The 2010 and 2009 share repurchase programs were completed during the third and first quarters of 2010, respectively.

Stockholder Rights Plan

In January 2009, we terminated our stockholders rights plan. The plan was adopted in 1997 and scheduled to expire in 2011. Under the rights plan, each share of our common stock had one “right” attached to it that entitled the holder to purchase our Series X Junior Participating Preferred Stock under the circumstances specified in the rights plan. No rights are outstanding or exercisable following termination of the plan.

Accumulated Other Comprehensive Income (Loss)

12 Months Ended

Dec. 31, 2010

Accumulated Other Comprehensive Income (Loss) [Abstract]

Accumulated Other Comprehensive Income (Loss)


13.	Accumulated Other Comprehensive Income (Loss)

Accumulated other comprehensive income (loss) consisted of the following:


	As of December 31,
(In millions)	2010			2009

Translation adjustments	$	(24.4	)	$	35.6
Unrealized gains (losses) on securites available for sale		12.4			11.3
Unrealized gains (losses) on foreign currency forward contracts		(9.8	)		1.5
Unfunded status of pension and postretirement benefit plans		0.2			2.1

Accumulated other comprehensive income (loss)	$	(21.6	)	$	50.5

Unrealized holding gains on securities available for sale is shown net of tax of $7.3 million and $6.6 million as of December 31, 2010 and 2009, respectively. Unrealized gains (losses) on foreign currency forward contracts are shown net of tax of $1.3 million, and $0.3 million as of December 31, 2010 and 2009, respectively. The unfunded status of pension and retirement benefit plans is shown net of tax as of December 31, 2010 and 2009. Tax amounts in both years were immaterial. For discussion of the unfunded status of pension and retirement benefit plans, please read Note 23, Employee Benefit Plans to these consolidated financial statements.

Amounts comprising noncontrolling interests, as reported in our consolidated statements of equity as of December 31, 2010 and 2009 included accumulated translation adjustments of $0.2 million and $2.4 million, respectively.

Comprehensive income (loss) and its components are presented in the consolidated statements of equity.

Earnings per Share

12 Months Ended

Dec. 31, 2010

Earnings per Share [Abstract]

Earnings per Share


14.	Earnings per Share

Basic and diluted earnings per share are calculated as follows:


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Numerator:
Net income attributable to Biogen Idec Inc.	$	1,005.3		$	970.1		$	783.2
Adjustment for net income allocable to preferred stock		(2.0	)		(1.7	)		(1.3	)

Net income used in calculating basic and diluted earnings per share	$	1,003.3		$	968.4		$	781.9

Denominator:
Weighted average number of common shares outstanding		252.3			287.4			292.3
Effect of dilutive securities:
Stock options and employee stock purchase plan		0.9			0.6			1.3
Restricted stock awards		—			—			0.1
Time-vested restricted stock units		1.6			1.4			1.3
Market stock units		0.1			—			—
Performance-vested restricted stock units settled in shares		—			0.1			—

Dilutive potential common shares		2.6			2.1			2.7

Shares used in calculating diluted earnings per share		254.9			289.5			295.0

The following amounts were not included in the calculation of net income per basic and diluted share because their effects were anti-dilutive:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Numerator:
Net income allocable to preferred stock	$	2.0	$	1.7	$	1.3
Denominator:
Stock options		4.6		8.5		6.9
Time-vested restricted stock units		0.1		2.1		1.5
Market stock units		—		—		—
Performance-vested restricted stock units		—		0.2		—
Convertible preferred stock		0.5		0.5		0.5

Total		5.2		11.3		8.9

Earnings per share for the years ended December 31, 2010 and 2009 reflects, on a weighted average basis, the repurchase of 40.3 million shares and 16.0 million shares, respectively of our common stock under our share repurchase authorizations.

Share-Based Compensation

12 Months Ended

Dec. 31, 2010

Share-Based Compensation [Abstract]

Share-based Compensation


15.	Share-based Compensation

Share-based Compensation Expense

The following table summarizes share-based compensation expense included within our consolidated statements of income:


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Research and development	$	62.7		$	60.8		$	59.9
Selling, general and administrative		123.6			106.4			93.8
Restructuring charges		6.8			—			—

Subtotal		193.1			167.2			153.7
Capitalized share-based compensation costs		(3.5	)		(6.3	)		(7.5	)

Share-based compensation expense included in total costs and expenses		189.6			160.9			146.2
Income tax effect		(60.3	)		(49.4	)		(45.4	)

Share-based compensation expense included in net income attributable to Biogen Idec Inc.	$	129.3		$	111.5		$	100.8

The following table summarizes share-based compensation expense associated with each of our share-based compensation programs:


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Stock options	$	26.1		$	21.6		$	20.0
Market stock units		10.0			—			—
Time-vested restricted stock units		129.4			133.7			125.6
Performance-vested restricted stock units settled in shares		5.3			4.6			1.1
Performance-vested restricted stock units settled in cash		15.0			—			—
Restricted stock awards		—			—			0.5
Employee stock purchase plan		7.3			7.3			6.5

Subtotal		193.1			167.2			153.7
Capitalized share-based compensation costs		(3.5	)		(6.3	)		(7.5	)

Share-based compensation expense included in total costs and expenses		189.6			160.9			146.2

Windfall tax benefits from vesting of stock awards, exercises of stock options and ESPP participation were $13.1 million, $3.4 million and $28.0 million in 2010, 2009 and 2008, respectively. These amounts have been calculated under the alternative transition method in accordance with U.S. GAAP.

As of December 31, 2010, unrecognized compensation cost related to unvested share-based compensation was approximately $130.5 million, net of estimated forfeitures. We expect to recognize the cost of these unvested awards over a weighted-average period of 1.3 years.

Share-Based Compensation Plans

We have three share-based compensation plans pursuant to which awards are currently being made: (1) the Biogen Idec Inc. 2006 Non-Employee Directors Equity Plan (2006 Directors Plan); (2) the Biogen Idec Inc. 2008 Omnibus Equity Plan (2008 Omnibus Plan); and (3) the Biogen Idec Inc. 1995 Employee Stock Purchase Plan (ESPP). We have six share-based compensation plans pursuant to which outstanding awards have been made, but from which no further awards can or will be made: (i) the IDEC Pharmaceuticals Corporation 1993 Non-Employee Directors Stock Option Plan; (ii) the IDEC Pharmaceuticals Corporation 1988 Stock Option Plan; (iii) the Biogen, Inc. 1985 Non-Qualified Stock Option Plan; (iv) the Biogen, Inc. 1987 Scientific Board Stock Option Plan; (v) the Biogen Idec Inc. 2003 Omnibus Equity Plan (2003 Omnibus Plan); and (vi) the Biogen Idec Inc. 2005 Omnibus Equity Plan (2005 Omnibus Plan). We have not made any awards pursuant to the 2005 Omnibus Plan since our stockholders approved the 2008 Omnibus Plan and do not intend to make any awards pursuant to the 2005 Omnibus Plan in the future, except that unused shares under the 2005 Omnibus Plan have been carried over for use under the 2008 Omnibus Plan.

Directors Plan

In May 2006, our stockholders approved the 2006 Directors Plan for share-based awards to our directors. Awards granted from the 2006 Directors Plan may include stock options, shares of restricted stock, restricted stock units, stock appreciation rights and other awards in such amounts and with such terms and conditions as may be determined by a committee of our Board of Directors, subject to the provisions of the plan. We have reserved a total of 1.6 million shares of common stock for issuance under the 2006 Directors Plan. The 2006 Directors Plan provides that awards other than stock options and stock appreciation rights will be counted against the total number of shares reserved under the plan in a 1.5-to-1 ratio.

Omnibus Plans

In June 2008, our stockholders approved the 2008 Omnibus Plan for share-based awards to our employees. Awards granted from the 2008 Omnibus Plan may include stock options, shares of restricted stock, restricted stock units, performance shares, shares of phantom stock, stock appreciation rights and other awards in such amounts and with such terms and conditions as may be determined by a committee of our Board of Directors, subject to the provisions of the plan. Shares of common stock available for issuance under the 2008 Omnibus Plan consist of 15.0 million shares reserved for this purpose, plus shares of common stock that remained available for issuance under the 2005 Omnibus Plan on the date that our stockholders approved the 2008 Omnibus Plan, plus shares that are subject to awards under the 2005 Omnibus Plan which remain unissued upon the cancellation, surrender, exchange or termination of such awards. The 2008 Omnibus Equity Plan provides that awards other than stock options and stock appreciation rights will be counted against the total number of shares available under the plan in a 1.5-to-1 ratio.

Stock Options

All stock option grants to employees are for a ten-year term and generally vest one-fourth per year over four years on the anniversary of the date of grant, provided the employee remains continuously employed with us. Stock option grants to directors are for ten-year terms and generally vest as follows: (1) grants made on the date of a director’s initial election to our Board of Directors vest one-third per year over three years on the anniversary of the date of grant and (2) grants made for service on our Board of Directors vest on the first anniversary of the date of grant, provided in each case that the director continues to serve on our Board of Directors through the vesting date. Options granted under all plans are exercisable at a price per share not less than the fair market value of the underlying common stock on the date of grant. The estimated fair value of options, including the effect of estimated forfeitures, is recognized over the options’ vesting periods. The fair value of the stock options granted in 2010, 2009 and 2008 was estimated as of the date of grant using a Black-Scholes option valuation model that uses the following weighted-average assumptions:


	For the Years Ended December 31,
	2010			2009			2008

Expected option life (in years)		4.5			4.7			5.1
Expected stock price volatility		30.8	%		39.3	%		34.4	%
Risk-free interest rate		2.0	%		1.9	%		2.4	%
Expected dividend yield		0.0	%		0.0	%		0.0	%
Per share grant-date fair value	$	16.52		$	18.00		$	20.85

The expected life of options granted is derived using assumed exercise rates based on historical exercise patterns and represents the period of time that options granted are expected to be outstanding. Expected stock price volatility is based upon implied volatility for our exchange-traded options and other factors, including historical volatility. After assessing all available information on either historical volatility, implied volatility, or both, we have concluded that a combination of both historical and implied volatility provides the best estimate of expected volatility. The risk-free interest rate used is determined by the market yield curve based upon risk-free interest rates established by the Federal Reserve, or non-coupon bonds that have maturities equal to the expected term. The dividend yield of zero is based upon the fact that we have not historically granted cash dividends, and do not expect to issue dividends in the foreseeable future. Stock options granted prior to January 1, 2006 were valued based on the grant date fair value of those awards, using the Black-Scholes option pricing model, as previously calculated for pro-forma disclosures.

The following table summarizes our stock option activity:


				Weighted
				Average
				Exercise
(In thousands, except weighted average exercise price)	Shares			Price

Outstanding at December 31, 2007		14,900		$	50.03

Granted		1,475		$	60.23
Exercised		(3,769	)	$	41.99
Cancelled		(506	)	$	55.70

Outstanding at December 31, 2008		12,100		$	53.53

Granted		1,031		$	49.96
Exercised		(637	)	$	40.16
Cancelled		(1,664	)	$	60.74

Outstanding at December 31, 2009		10,830		$	52.88

Granted		124		$	57.38
Exercised		(3,455	)	$	46.86
Cancelled		(332	)	$	61.96

Outstanding at December 31, 2010		7,167		$	55.43

Of the options outstanding, 6.0 million were exercisable as of December 31, 2010. The exercisable options had a weighted-average exercise price of $55.68. The aggregate intrinsic value of options exercisable as of December 31, 2010 was $69.4 million. The weighted average remaining contractual term for options exercisable as of December 31, 2010 was 3.6 years.

A total of 6.9 million vested and expected to vest options were outstanding as of December 31, 2010. These vested and expected to vest options had a weighted average exercise price of $55.48 and an aggregated intrinsic value of $81.3 million. The weighted average remaining contractual term of vested and expected to vest options as of December 31, 2010 was 4.2 years.

The total intrinsic values of options exercised in 2010, 2009 and 2008 were $50.5 million, $6.7 million and $85.1 million, respectively. The aggregate intrinsic values of options outstanding as of December 31, 2010 totaled $84.9 million. The weighted average remaining contractual term for options outstanding as of December 31, 2010 was 4.3 years.

The following table summarizes the amount of tax benefit realized for stock options and cash received from the exercise of stock options:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Tax benefit realized for stock options	$	16.0	$	1.5	$	28.0
Cash received from the exercise of stock options	$	160.0	$	25.2	$	158.3

Market Stock Units (MSUs) and Cash Settled Performance Shares (CSPSs)

Beginning in the first quarter of 2010, we revised our long term incentive program to include two new forms of equity-based compensation awards to certain employees: restricted stock units which will vest based on stock price performance, referred to as MSUs, and performance-vested restricted stock units which will be settled in cash, referred to as CSPSs. We will apply forfeiture rate assumptions to these types of awards similar to those utilized by us when accounting for our other share-based compensation programs.

Market Stock Units

During 2010, approximately 405,000 MSUs were granted with a weighted average grant date fair value of $61.87. MSU awards vest in four equal annual increments beginning on the anniversary of the grant date. The vesting of these awards is subject to the respective employee’s continued employment. The number of MSUs reflected as granted represents the target number of units that are eligible to be earned based on the attainment of certain market-based criteria involving our stock price. The number of MSUs earned is calculated at each annual anniversary from the date of grant over the respective vesting periods, resulting in multiple performance periods. Participants may ultimately earn between 0% and 150% of the target number of units granted based on actual stock performance. Accordingly, additional MSUs may be issued or currently outstanding MSUs may be cancelled upon final determination of the number of awards earned.

We have valued the granted MSUs using a lattice model with a Monte Carlo simulation. This valuation methodology utilizes several key assumptions, including the 60 calendar day average closing stock price on grant date, expected volatility of our stock price, risk-free rates of return and expected dividend yield. The assumptions used in our valuation are summarized as follows:


Expected dividend yield		0%
Range of excepted stock price volatility		28.3% - 38.8%
Range of risk-free interest rates		0.3% - 2.0%
60 calendar day average stock price on grant date		$49.08 - $54.12

Cash Settled Performance Shares

During 2010, approximately 380,000 CSPSs were granted. CSPS awards vest in three equal annual increments beginning on the anniversary of the grant date. The vesting of these awards is subject to the respective employee’s continued employment. The number of CSPSs reflected as granted in 2010 represents the target number of units that are eligible to be earned based on the attainment of certain performance measures established at the beginning of the performance period, which ended December 31, 2010. Participants may ultimately earn between 0% and 200% of the target number of units granted based on the degree of actual performance metric achievement. Accordingly, additional CSPSs may be issued or currently outstanding CSPSs may be cancelled upon final determination of the number of units earned. CSPSs are settled in cash based on the 60 calendar day average closing stock price through each vesting date once the actual vested and earned number of units is known.

Time-Vested Restricted Stock Units (RSUs)

RSUs awarded to employees generally vest no sooner than one-third per year over three years on the anniversary of the date of grant, or upon the third anniversary of the date of the grant, provided the employee remains continuously employed with us, except as otherwise provided in the plan. Shares of our common stock will be delivered to the employee upon vesting, subject to payment of applicable withholding taxes. RSUs awarded to directors for service on our Board of Directors vest on the first anniversary of the date of grant, provided in each case that the director continues to serve on our Board of Directors through the vesting date. Shares of our common stock will be delivered to the director upon vesting and are not subject to any withholding taxes. The fair value of all RSUs is based on the market value of our stock on the date of grant. Compensation expense, including the effect of forfeitures, is recognized over the applicable service period.

The following table summarizes our RSU activity:


				Weighted
				Average
				Grant Date
(In thousands, except weighted average grant date fair value)	Shares			Fair Value

Unvested at December 31, 2007		4,592		$	49.12

Granted		3,129		$	58.42
Vested		(1,645	)	$	47.93
Forfeited		(499	)	$	53.95

Unvested at December 31, 2008		5,577		$	54.26

Granted		2,674		$	48.93
Vested		(2,421	)	$	52.08
Forfeited		(445	)	$	53.02

Unvested at December 31, 2009		5,385		$	52.72

Granted		2,067		$	54.79
Vested		(2,829	)	$	53.39
Forfeited		(400	)	$	52.93

Unvested at December 31, 2010		4,223		$	53.26

Performance-Vested Restricted Stock Units (PVRSUs)

The following table summarizes our PVRSU activity:


				Weighted
				Average
				Grant Date
(In thousands, except weighted average grant date fair value)	Shares			Fair Value

Unvested at December 31, 2007		120		$	51.55

Granted		—		$	—
Vested		(27	)	$	49.33
Forfeited		(3	)	$	49.33

Unvested at December 31, 2008		90		$	52.29

Granted		325		$	49.42
Vested		(30	)	$	52.29
Forfeited		(97	)	$	51.30

Unvested at December 31, 2009		288		$	49.39

Granted		4		$	53.64
Vested		(129	)	$	49.69
Forfeited		(9	)	$	49.56

Unvested at December 31, 2010		154		$	49.24

Grant Activity

In 2009, approximately 325,000 PVRSUs were granted with a weighted average grant date fair value of $49.42 per share. The number of PVRSUs reflected as granted represents the target number of shares that are eligible to vest in full or in part and are earned subject to the attainment of certain performance criteria established at the beginning of the performance period, which ended December 31, 2009. Participants may ultimately earn up to 200% of the target number of shares granted in the event that the maximum performance thresholds are attained. Accordingly, additional PVRSUs may be issued upon final determination of the number of awards earned.

Once the earned number of performance-vested awards has been determined, the earned PVRSUs will then vest in three equal increments on (1) the later of the first anniversary of the grant date or the date of results determination; (2) the second anniversary of the grant date; and (3) the third anniversary of the grant date. The vesting of these awards is also subject to the respective employees’ continued employment. Compensation expense associated with these PVRSUs is initially based upon the number of shares expected to vest after assessing the probability that certain performance criteria will be met and the associated targeted payout level that is forecasted will be achieved, net of estimated forfeitures. Cumulative adjustments are recorded quarterly to reflect subsequent changes in the estimated outcome of performance-related conditions until the date results are determined.

Restricted Stock Awards (RSAs)

In 2005, we awarded restricted common stock to our employees under the 2005 Omnibus Plan and the 2003 Omnibus Plan. The RSAs granted under the 2003 Omnibus Plan vested in full on the third anniversary of the date of grant for employees that remained continuously employed with us through the vesting dates. The RSAs granted under the 2005 Omnibus Plan vested at a rate of approximately one-third per year over three years on the anniversary of the date of grant for employees that remained continuously employed with us through the vesting dates.

The fair value of all time-vested RSAs is based on the market value of our stock on the date of grant. Compensation expense, including the effect of forfeitures, is recognized over the applicable service period. All awards of restricted stock were fully vested as of December 31, 2008.

Employee Stock Purchase Plan (ESPP)

The following table summarizes our ESPP activity:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Shares issued under ESPP		0.6		0.6		0.5
Cash received under ESPP	$	23.5	$	22.6	$	21.3

Other

As part of the employee severance and benefits packages offered to employees affected by our recent workforce reduction, we agreed to settle certain existing equity awards in cash, which resulted in an incremental charge of approximately $6.8 million recognized in the fourth quarter of 2010. This charge is reflected within our consolidated statement of income as a component of our total restructuring charge incurred in 2010.

CEO Agreements

On June 30, 2010, we announced that George A. Scangos, Ph.D., was appointed Chief Executive Officer and a member of the Board of Directors, effective July 15, 2010. Under the terms of his employment agreement with the Company, Dr. Scangos received a grant of 63,165 RSUs and a grant of 56,905 MSUs which are included within the total award grants described above. Awards made to Dr. Scangos are subject to the same terms and conditions as other grants except that if Dr. Scangos retires from the Company after reaching the age of 65, any outstanding and unvested RSUs and CSPSs, if granted, will continue to vest as if Dr. Scangos continued to be employed by the Company.

Dr. Scangos succeeded James C. Mullen, who retired as our President and Chief Executive Officer on June 8, 2010. Under the terms of the transition agreement we entered into with Mr. Mullen dated January 4, 2010, we agreed, amongst other provisions, to vest all of Mr. Mullen’s then-unvested equity awards on the date of his retirement and allow Mr. Mullen to exercise his vested stock options until June 8, 2013 or their expiration, whichever is earlier. The modifications to Mr. Mullen’s existing stock options, RSUs and PVRSUs resulted in an incremental charge of approximately $18.6 million, which was recognized evenly over the service period from January 4, 2010 to June 8, 2010, as per the terms of the transition agreement.

Income Taxes

12 Months Ended

Dec. 31, 2010

Income Taxes [Abstract]

Income Taxes


16.	Income Taxes

Income Tax Expense

Income before income tax provision and the income tax expense consist of the following:


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Income before income taxes (benefit):
Domestic	$	846.4		$	1,073.8		$	829.2
Foreign		383.5			258.9			326.7

Total	$	1,229.9		$	1,332.7		$	1,155.9

Income tax expense (benefit):
Current
Federal	$	357.7		$	439.9		$	431.2
State		19.6			3.1			24.3
Foreign		35.4			50.0			49.8

Total	$	412.7		$	493.0		$	505.3

Deferred
Federal	$	(70.6	)	$	(94.8	)	$	(119.2	)
State		(6.6	)		(39.0	)		(20.0	)
Foreign		(4.2	)		(3.6	)		(0.3	)

Total	$	(81.4	)	$	(137.4	)	$	(139.5	)

Total income tax expense	$	331.3		$	355.6		$	365.8

Deferred Tax Assets and Liabilities

Significant components of our deferred tax assets and liabilities are summarized as follows:


	As of December 31,
(In millions)	2010			2009

Deferred tax assets
Tax credits	$	47.6		$	35.2
Inventory, other reserves and accruals		203.1			166.4
Capitalized costs		6.7			8.7
Intangibles, net		61.8			83.2
Net operating loss		35.3			30.5
Share-based compensation		64.4			60.8
Other		70.3			60.6
Valuation allowance		(10.8	)		—

Total deferred tax assets	$	478.4		$	445.4

Deferred tax liabilities
Purchased intangible assets	$	(446.1	)	$	(475.4	)
Unrealized gain on investments and cumulative translation adjustment		(6.6	)		(6.3	)
Depreciation, amortization and other		(114.4	)		(115.6	)

Total deferred tax liabilities	$	(567.1	)	$	(597.3	)

Tax Rate

Reconciliation between the U.S. federal statutory tax rate and our effective tax rate is summarized as follows:


	For the Years Ended December 31,
	2010			2009			2008

Statutory rate		35.0	%		35.0	%		35.0	%
State taxes		1.7			(0.1	)		1.6
Taxes on foreign earnings		(10.7	)		(5.0	)		(5.8	)
Credits and net operating loss utilization		(3.0	)		(3.8	)		(2.9	)
Purchased intangible assets		1.9			2.0			3.7
IPR&D		5.0			—			0.8
Permanent items		(2.0	)		(1.3	)		(0.9	)
Other		(1.0	)		(0.1	)		0.1

Effective tax rate		26.9	%		26.7	%		31.6	%

As of December 31, 2010, we had net operating losses and general business credit carry forwards for federal income tax purposes of approximately $55.8 million and $14.8 million, respectively, which begin to expire in 2020. Additionally, for state income tax purposes, we had net operating loss carry forwards of approximately $184.7 million, which began to expire in 2010. For state income tax purposes, we also had research and investment credit carry forwards of approximately $56.8 million, of which approximately $53.4 million begin to expire in 2011, with the remainder having no prescribed expiration date.

In assessing the realizability of our deferred tax assets, we have considered whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. In making this determination, under the applicable financial reporting standards, we are allowed to consider the scheduled reversal of deferred tax liabilities, projected future taxable income, and tax planning strategies. Our estimates of future taxable income take into consideration, among other items, our estimates of future income tax deductions related to the exercise of stock options. Based upon the level of historical taxable income and income tax liability and projections for future taxable income over the periods in which the deferred tax assets are utilizable, we believe it is more likely than not that we will realize the benefits of the deferred tax assets of our wholly owned subsidiaries. At December 31, 2010, we have a partial valuation allowance on the deferred tax assets of a variable interest entity which we consolidate, based on uncertainties related to the realization of some of those assets. In the event that actual results differ from our estimates or we adjust our estimates in future periods, we may need to establish a valuation allowance, which could materially impact our financial position and results of operations.

As of December 31, 2010, undistributed foreign earnings of non-U.S. subsidiaries and other basis differences included in consolidated retained earnings aggregated approximately $2.4 billion. We intend to reinvest these earnings indefinitely in operations outside the U.S. It is not practicable to estimate the amount of additional tax that might be payable if such earnings were remitted to the U.S.

Accounting for Uncertainty in Income Taxes

A reconciliation of the beginning and ending amount of our unrecognized tax benefits is summarized as follows:


(In millions)	2010			2009			2008

Balance at January 1,	$	147.1		$	249.6		$	221.1
Additions based on tax positions related to the current period		3.6			14.4			21.8
Additions for tax positions of prior periods		13.3			77.4			20.4
Reductions for tax positions of prior periods		(18.5	)		(88.7	)		(13.7	)
Statute expirations		(3.7	)		—			—
Settlements		(20.3	)		(105.6	)		—

Balance at December 31,	$	121.5		$	147.1		$	249.6

We and our subsidiaries are routinely examined by various taxing authorities. We file income tax returns in the U.S. federal jurisdiction, and various states and foreign jurisdictions. With few exceptions, we are no longer subject to U.S. federal tax examination for years before 2007 or state, local, or non-U.S. income tax examinations by tax authorities for years before 2001.

Included in the balance of unrecognized tax benefits as of December 31, 2010, 2009, and 2008 are $26.2 million, $42.8 million and $155.1 million (net of the federal benefit on state issues), respectively, of unrecognized tax benefits that, if recognized, would affect the effective income tax rate in future periods.

We do not anticipate any significant changes in our positions in the next twelve months other than expected settlements which have been classified as current liabilities within the accompanying balance sheet and the potential resolution of our litigation with the Massachusetts Department of Revenue, as described below.

We recognize potential interest and penalties accrued related to unrecognized tax benefits in income tax expense. During 2010, we recognized net interest expense of $0.7 million. In 2009, as we settled certain uncertain tax positions, we recognized a net interest benefit of approximately $3.1 million. During 2008, we recognized approximately $16.1 million in interest expense. We have accrued approximately $29.4 million and $33.1 million for the payment of interest as of December 31, 2010 and 2009, respectively.

Contingency

In 2006, the Massachusetts Department of Revenue (DOR) issued a Notice of Assessment against Biogen Idec MA Inc. (BIMA), one of our wholly-owned subsidiaries, for $38.9 million of corporate excise tax for 2002, which includes associated interest and penalties. The assessment asserts that the portion of sales attributable to Massachusetts (sales factor), the computation of BIMA’s research and development credits and certain deductions claimed by BIMA were not appropriate, resulting in unpaid taxes for 2002. In December 2006, we filed an abatement application with the DOR seeking abatement for 2001, 2002 and 2003, which was denied. In July 2007, we filed a petition with the Massachusetts Appellate Tax Board (the Massachusetts ATB) seeking, among other items, abatements of corporate excise tax for 2001, 2002 and 2003 and adjustments in certain credits and credit carryforwards for 2001, 2002 and 2003. Issues before the Board include the computation of BIMA’s sales factor for 2001, 2002 and 2003, computation of BIMA’s research credits for those same years, and the availability of deductions for certain expenses and partnership flow-through items. We anticipate that the hearing on our petition will take place in the second quarter of 2011.

On June 8, 2010, we received Notices of Assessment from the DOR against BIMA for $103.5 million of corporate excise tax, including associated interest and penalties, related to our 2004, 2005 and 2006 tax filings. The asserted basis for these assessments is consistent with that for 2002. Including associated interest and penalties, assessments related to periods under dispute totaled $142.4 million. In August 2010, we filed an abatement application with the DOR seeking abatement for 2004, 2005 and 2006, which the DOR denied in December 2010. We intend to appeal the denial to the Massachusetts ATB. For all periods under dispute, we believe that positions taken in our tax filings are valid and believe that we have meritorious defenses in these disputes. We intend to contest these matters vigorously. Our tax filings for 2007 and 2008 have not yet been audited by the DOR but have been prepared in a manner consistent with prior filings which may result in an assessment for those years. Due to tax law changes effective January 1, 2009, the computation and deductions at issue in previous tax filings will not be part of our tax filings in Massachusetts starting in 2009.

We believe that these assessments do not impact the level of liabilities for income tax contingencies. However, there is a possibility that we may not prevail in defending all of our assertions with the DOR. If these matters are resolved unfavorably in the future, the resolution could have a material adverse impact on our future effective tax rate and our results of operations.

Settlements

During 2009, the IRS completed its examination of our consolidated income tax returns for our fiscal years 2005 and 2006. We then reached an agreement to pay an amount to settle all matters related to the 2005 and 2006 years and resolve those matters under appeal related to 2003 and 2004. There are no remaining U.S. federal income tax contingencies for the periods prior to tax year 2007.

As a result of the 2009 completion of several domestic audits, we made payments totaling approximately $13.8 million during 2010 and $118.0 million during 2009. In addition, we expect that we will make additional payments totaling approximately $76.1 million in the first half of 2011 related to these audits, which have been accrued as of December 31, 2010. We also reduced our net unrecognized tax benefits during 2009 by approximately $123.5 million, of which approximately $28.0 million was recorded as a benefit in our consolidated statement of income in 2009.

Other Consolidated Financial Statement Detail

12 Months Ended

Dec. 31, 2010

Other Consolidated Financial Statement Detail [Abstract]

Other Consolidated Financial Statement Detail


17.	Other Consolidated Financial Statement Detail

Supplemental Cash Flow Information

Supplemental disclosure of cash flow information for the years ended December 31, 2010, 2009, and 2008 is as follows:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Cash paid during the year for:
Interest	$	68.1	$	68.1	$	40.0
Income taxes	$	394.7	$	745.4	$	372.0

In December 2010, upon completion of our acquisition of Panima, we recorded $110.9 million of in process research and development and $25.6 million of goodwill. In addition, we also assumed a contingent consideration liability of $81.2 million and a deferred tax liability of $23.7 million.

Other Income (Expense), Net

Components of other income (expense), net, are summarized as follows:


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Interest income	$	22.3		$	48.5		$	72.1
Interest expense		(36.1	)		(35.8	)		(52.0	)
Impairments of investments		(21.3	)		(10.6	)		(60.3	)
Gain (loss) on sales of investments, net		16.3			22.8			(1.1	)
Foreign exchange gains (losses), net		(3.5	)		11.4			(9.8	)
Other, net		3.3			1.0			(6.6	)

Total other income (expense), net	$	(19.0	)	$	37.3		$	(57.7	)

Other Current Assets

Other current assets consist of the following:


	As of December 31,
(In millions)	2010		2009

Deferred tax assets	$	112.2	$	88.8
Prepaid taxes		31.4		11.0
Receivable from collaborations		7.3		5.3
Interest receivable		4.9		10.6
Other prepaid expenses		47.9		41.6
Other		12.1		20.6

Total other current assets	$	215.8	$	177.9

Accrued Expenses and Other

Accrued expenses and other consists of the following:


	As of December 31,
(In millions)	2010		2009

Employee compensation and benefits	$	159.7	$	127.1
Revenue-related rebates		90.1		52.0
Restructuring charges		66.4		—
Royalties and licensing fees		45.1		41.8
Deferred revenue		41.3		38.7
Collaboration expenses		31.6		35.7
Clinical development expenses		24.4		43.2
Interest payable		21.6		21.6
Construction in progress accrual		16.4		12.8
Current portion of contingent consideration		11.9		—
Other		157.4		127.9

Total accrued expense and other	$	665.9	$	500.8

For a discussion of restructuring charges accrued as of December 31, 2010, please read Note 3, Restructuring to these consolidated financial statements.

Gain on Sale of Property, Plant and Equipment, net

In 2008, we sold the development rights on a parcel of land in Cambridge, MA for $11.4 million in a non-monetary transaction and we recorded a pre-tax gain of approximately $9.2 million on the sale.

Investments in Variable Interest Entities

12 Months Ended

Dec. 31, 2010

Investments in Variable Interest Entities [Abstract]

Investments in Variable Interest Entities


18.	Investments in Variable Interest Entities

Consolidated Variable Interest Entities

Our consolidated financial statements include the financial results of variable interest entities in which we are the primary beneficiary.

Investments in Joint Ventures

We consolidate the operations of Biogen Dompé SRL and Biogen Dompé Switzerland GmbH, our respective sales affiliates in Italy and Switzerland, as we retain the contractual power to direct the activities of these entities which most significantly and directly impact their economic performance. The activity of each of these joint ventures is significant to our overall operations. The assets of these joint ventures are restricted, from the standpoint of Biogen Idec, in that they are not available for our general business use outside the context of each joint venture. The holders of the liabilities of each joint venture, including the credit line from Dompé have no recourse to Biogen Idec.

Included within our consolidated balance sheet at December 31, 2010 are total joint venture assets and liabilities of $159.2 million and $63.3 million, respectively. The joint venture’s most significant assets are accounts receivable from the ordinary course of business of $124.2 million.

Other than the line of credit from us and Dompé Farmaceutici SpA to Biogen-Dompé SRL, as described in Note 11, Indebtedness, we have provided no financing to these joint ventures. In addition, Biogen-Dompé SRL has an operating lease for office space as well as a contract for the provision of administrative services with Dompé Farmaceutici SpA.

Knopp

In August 2010, we entered into a license agreement with Knopp Neurosciences, Inc. (Knopp), a subsidiary of Knopp Holdings, LLC, for the development, manufacture and commercialization of dexpramipexole, an orally administered small molecule in clinical development for the treatment of amyotrophic lateral sclerosis (ALS). Under the terms of the license agreement we made a $26.4 million upfront payment and agreed to pay Knopp up to an additional $265.0 million in development and sales-based milestone payments, as well as royalties on future commercial sales. In exchange, we will be responsible for all development activities and, if successful, we will also be responsible for the manufacture and global commercialization of dexpramipexole. Royalties are payable to Knopp on a country by country basis until the later of 10 years from the first commercial sale of a dexpramipexole product or the loss of exclusivity in such country. In addition, we also purchased 30.0% of the Class B common shares of Knopp for $60.0 million.

Due to the terms of the license agreement with Knopp, we have determined that we are the primary beneficiary of Knopp as we have the power to direct the activities that most significantly impact Knopp’s economic performance. As such, we consolidate the results of Knopp. The assets and liabilities of Knopp are not significant to our financial position or results of operations.

As the license agreement with Knopp only gives us access to the underlying intellectual property of dexpramipexole and we did not acquire any employees or other processes, we have determined that this transaction was an acquisition of an asset rather than a business. Therefore, we have recorded an IPR&D charge of approximately $205.0 million upon the initial consolidation of Knopp, which is included within our consolidated statement of income for 2010. The amount allocated to IPR&D represents the fair value of the intellectual property of Knopp, which as of the effective date of the agreement, had not reached technological feasibility and had no alternative future use. This charge was determined using internal models based on projected revenues and development costs and adjusted for industry-specific probabilities of success. Estimated revenues from dexpramipexole are expected to be recognized beginning in 2014. A discount rate of 14% was used in the valuation of this asset, which we believe to be commensurate with the stage of development and level of risk associated with the underlying biologic compound. Within the hierarchy of fair value measurements, this IPR&D charge is classified as having a Level 3 fair value. We have attributed approximately $145.0 million of the IPR&D charge to the noncontrolling interest.

Future development and sales-based milestone payments will be reflected within our consolidated statements of income as a charge to the noncontrolling interest, net of tax, when such milestones are achieved. Although we have assumed responsibility for the development of dexpramipexole, we may also be required to reimburse certain Knopp expenses directly attributable to the license agreement. Any additional amounts incurred by Knopp that we reimburse will be reflected within total cost and expenses in our consolidated statements of income.

A summary of activity related to this collaboration, excluding the initial accounting for the consolidation of Knopp, is as follows:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Total upfront payments made to Knopp	$	26.4	$	—	$	—
Total development expense incurred by the collaboration excluding upfront and milestone payments	$	5.0	$	—	$	—
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	31.4	$	—	$	—
Collaboration expense attributed to noncontrolling interests, net of tax	$	—	$	—	$	—

Neurimmune SubOne AG

In 2007, we entered into a collaboration agreement with Neurimmune SubOne AG (Neurimmune), a subsidiary of Neurimmune AG, for the development and commercialization of antibodies for the treatment of Alzheimer’s disease. Neurimmune conducts research to identify potential therapeutic antibodies and we are responsible for the development, manufacturing and commercialization of all products. Based upon our current development plans, we may pay Neurimmune up to $360.0 million in remaining milestone payments, as well as royalties on sales of any resulting commercial products.

We have determined that we are the primary beneficiary of Neurimmune because we have the power through the collaboration to direct the activities that most significantly impact SubOne’s economic performance and are required to fund 100% of the research and development costs incurred in support of the collaboration agreement.

The assets and liabilities of Neurimmune are not significant as it is a research and development organization. Amounts that are incurred by Neurimmune for research and development expenses incurred in support of the collaboration that we reimburse are reflected in research and development expense in our consolidated statements of income. Future milestone payments will be reflected within our consolidated statements of income as a charge to the noncontrolling interest, net of tax, when such milestones are achieved.

A summary of activity related to this collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Milestone payments made to Neurimmune	$	—	$	7.5	$	10.5
Total development expense incurred by the collaboration, excluding upfront and milestone payments	$	15.5	$	9.0	$	5.9
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	15.5	$	16.5	$	16.4
Collaboration expense attributed to noncontrolling interests, net of tax	$	1.0	$	—	$	—

A summary of activity related to this collaboration since inception, along with an estimate of additional future development expenses expected to be incurred by us, is as follows:


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments made to Neurimmune	$	20.0
Total development expense incurred by Biogen Idec excluding upfront and milestone payments	$	31.0
Estimate of additional amounts to be incurred by us in development of the lead compound	$	539.5

We have provided no financing to Neurimmune other than previously contractually required amounts.

In December 2010, we completed our acquisition of Panima from Neurimmune AG, a related party to this collaboration. For a more detailed description of this transaction, please read Note 2, Acquisitions to these consolidated financial statements.

Cardiokine

On October 28, 2010, we agreed to terminate our collaboration with Cardiokine Biopharma, LLC (Cardiokine), a subsidiary of Cardiokine Inc., for the development of lixivaptan effective November 1, 2010. Under the terms of the agreement, we have funded our share of the development costs through the effective date and made a final payment of $25.0 million to Cardiokine, the costs of which have been reflected within noncontrolling interest. The termination triggered the return of all rights to lixivaptan to Cardiokine.

We had previously determined that we were the primary beneficiary of Cardiokine because we had the power through the collaboration to direct the activities that most significantly impact Cardiokine’s economic performance and were required to fund 90% of the development costs. Upon terminating our development interest, we have ceased consolidating the results of Cardiokine. As such, we consolidated the results of Cardiokine through October 31, 2010. The assets and liabilities of Cardiokine were not significant as it is a research and development organization. Amounts that are incurred by Cardiokine for research and development expense incurred in support of the collaboration that we reimbursed are reflected in research and development expense in our consolidated statements of income.

A summary of activity related to this collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Milestone payments made to Cardiokine	$	—	$	20.0	$	—
Total expense incurred by collaboration	$	51.1	$	66.5	$	50.5
Biogen Idec’s share of expense incurred by the collaboration reflected within our consolidated statements of income	$	46.0	$	79.8	$	45.5
Collaboration expense attributed to noncontrolling interests, net of tax	$	5.1	$	6.7	$	5.0

In addition to the $25.0 million termination payment we made in November 2010, we have made upfront and milestone payments to Cardiokine totaling approximately $70.0 million since the inception of this collaboration. Additionally, excluding termination, upfront and milestone payments, we have incurred development expense totaling approximately $173.9 million under this collaboration agreement.

Unconsolidated Variable Interest Entities

We have relationships with other variable interest entities which we do not consolidate as we lack the power to direct the activities that significantly impact the economic success of these entities. These relationships include investments in certain biotechnology companies and research collaboration agreements. For additional information related to our significant collaboration arrangements with unconsolidated variable interest entities, please read Note 19, Collaborations to these consolidated financial statements.

As of December 31, 2010 the total carrying value of our investments in biotechnology companies that we have determined to be variable interest entities is $22.9 million. Our maximum exposure to loss related to these variable interest entities is limited to the carrying value of our investments.

We have entered into research collaborations with certain variable interest entities where we are required to share or fund certain development activities. These development activities are included in research and development expense within our consolidated statements of income, as they are incurred. Depending on the collaborative arrangement, we may record funding receivables or payable balances with our partners, based on the nature of the cost-sharing mechanism and activity within the collaboration. As of December 31, 2010, we have no significant receivables or payables related to cost sharing arrangements with unconsolidated variable interest entities.

We have provided no financing to these variable interest entities other than previously contractually required amounts.

Collaborations

12 Months Ended

Dec. 31, 2010

Collaborations [Abstract]

Collaborations


19.	Collaborations

In connection with our business strategy, we have entered into various collaboration agreements which provide us with rights to develop, produce and market products using certain know-how, technology and patent rights maintained by our collaborative partners. Terms of the various collaboration agreements may require us to make milestone payments upon the achievement of certain product research and development objectives and pay royalties on future sales, if any, of commercial products resulting from the collaboration.

Genentech (Roche Group)

We collaborate with Genentech, Inc., a wholly-owned member of the Roche Group, on the development and commercialization of RITUXAN and other anti-CD20 products. Our collaboration rights are limited to the U.S. and our rights to products licensed by Genentech are dependent upon Genentech’s underlying license rights.

Our collaboration agreement does not have a fixed term and will continue in effect until we mutually agree to terminate the collaboration, except that if we undergo a change in control, as defined in the collaboration agreement, Genentech has the right to present an offer to buy the rights to RITUXAN and we must either accept Genentech’s offer or purchase Genentech’s rights on the same terms as its offer. Genentech will also be deemed concurrently to have purchased our rights to the other anti-CD20 products now in development in exchange for a royalty. Our collaboration with Genentech was created through a contractual arrangement and not through a joint venture or other legal entity.

In October 2010, we amended our collaboration agreement with Genentech with regard to the development of ocrelizumab and agreed to terms for the development of GA101, as summarized below. This amendment did not have an impact on our share of the co-promotion operating profits of RITUXAN in 2010.

Ocrelizumab

Genentech is now solely responsible for the further development and commercialization of ocrelizumab and funding future costs. Genentech cannot develop ocrelizumab in CLL, NHL or RA without our consent. We will receive tiered royalties between 13.5% and 24% on U.S. sales of ocrelizumab. Commercialization of ocrelizumab will not impact the percentage of the co-promotion profits we receive for RITUXAN.

GA101

We will pay 35% of the development and commercialization expenses of GA101 and will receive between 35% and 39% of the profits of GA101 based upon the achievement of certain sales milestones. Before the October 2010 amendment and restatement of our collaboration agreement, we had paid 30% of the GA101 development expenses. During the fourth quarter of 2010, we paid approximately $10.0 million to compensate Genentech for our increased share of such previously incurred expenses. Commercialization of GA101 will impact our percentage of the co-promotion profits for RITUXAN, as summarized in the table below.

RITUXAN

While Genentech is responsible for the worldwide manufacturing of RITUXAN, development and commercialization rights and responsibilities under this collaboration are divided as follows:

U.S.

We share with Genentech co-exclusive rights to develop, commercialize and market RITUXAN in the U.S. For 2010, 2009 and 2008, we contributed to the marketing and continued development of RITUXAN by maintaining a limited sales force dedicated to RITUXAN and performing limited development activity. However, during the fourth quarter of 2010, we agreed with Genentech to eliminate our current RITUXAN oncology and rheumatology sales force, with Genentech assuming sole responsibility for the U.S. sales and marketing of RITUXAN. For 2010, 2009 and 2008, we were reimbursed $58.3 million, $65.6 million and $59.7 million, respectively, for sales and marketing activities performed in support of RITUXAN.

Canada

We and Genentech have assigned our rights under our collaboration agreement with respect to Canada to Roche.

Outside the U.S. and Canada

We have granted Genentech exclusive rights to develop, commercialize and market RITUXAN outside the U.S. and Canada. Under the terms of separate sublicense agreements between Genentech and Roche, development and commercialization of RITUXAN outside the U.S. and Canada is the responsibility of Roche and its sublicensees. We do not have any direct contractual arrangements with Roche or it sublicensees.

Under the terms of the collaboration agreement, we will be paid royalties between 10% and 12% on sales of RITUXAN outside the U.S. and Canada, with the royalty period lasting 11 years from the first commercial sale of RITUXAN on a country-by-country basis. The royalty period for sales of RITUXAN has expired in the majority of European countries. For substantially all of the remaining royalty-bearing sales of RITUXAN in the rest of world, the royalty period will expire through 2012.

Co-promotion Profit-sharing Formula

Our current pretax co-promotion profit-sharing formula for RITUXAN, which resets annually, provides for a 30% share of co-promotion profits on the first $50.0 million of co-promotion operating profit with our share increasing to 40% if co-promotion operating profits exceed $50.0 million. Under the amended agreement, our share of the co-promotion profits for RITUXAN will change, as summarized in the table below, upon the following events:


	•	First New Product FDA Approval: the FDA’s first approval of an anti-CD20 product other than ocrelizumab and GA101 that is acquired or developed by Genentech and is subject to the collaboration agreement (New Product).

	•	First Non-CLL GA101 FDA Approval: the FDA’s first approval of GA101 in an indication other than CLL.

	•	GA101 CLL Sales Trigger: the first day of the quarter after U.S. gross sales of GA101 in any consecutive 12 month period reach $500.0 million.

Our share of the co-promotion operating profits for RITUXAN is calculated as follows:


				Before First New Product FDA Approval
	After First New			First Non-CLL GA101			GA101 CLL Sales
	Product FDA			FDA Approval Occurs			Trigger Occurs
Co-promotion Operating Profits†	Approval			First			First

I. First $50.0 million		30	%		30	%		30	%
II. Above $50.0 million		—			—			35	%
A. Until First GA101 Threshold Date		38	%		39	%		—
B. After First GA101 Threshold Date
1(a). Until First Threshold Date		37.5	%		—			—
1(b). After First Threshold Date and until Second Threshold Date		35	%		—			—
1(c). After Second Threshold Date		30	%		—			—
2. Until Second GA101 Threshold Date		—			37.5	%		—
C. After Second GA101 Threshold Date		—			35	%		—


†		First GA101 Threshold Date means the earlier of (1) the date of the First Non-CLL GA101 FDA Approval if U.S. gross sales of GA101 for the preceding consecutive 12 month period were at least $150.0 million or (2) the first day of the calendar quarter after the date of the First Non-CLL GA101 FDA Approval that U.S. gross sales of GA101 within any consecutive 12 month period have reached $150.0 million.

		Second GA101 Threshold Date means the first day of the calendar quarter after U.S. gross sales of GA101 within any consecutive 12 month period have reached $500.0 million.

		First Threshold Date means the earlier of (1) the GA101 CLL Sales Trigger, (2) the Second GA101 Threshold Date and (3) the later of (a) the first date that U.S. gross sales of New Products in any calendar year reach $150.0 million and (b) January 1 of the calendar year following the calendar year in which the First New Product FDA Approval occurs if gross sales of New Products reached $150.0 million within the same calendar year in which the First New Product FDA Approval occurred.

		Second Threshold Date means the later of (1) the first date that U.S. gross sales of New Products in any calendar year reach $350.0 million and (2) January 1 of the calendar year following the calendar year in which the First Threshold Date occurs.

Our collaboration agreement also provides that we will be paid low single digit royalties on sales outside the U.S. and Canada of new anti-CD20 products developed or licensed by Genentech or controlled by us. These royalties will be payable for a period of 11 years from the first commercial sale of such products on a country-by-country basis.

Unconsolidated Joint Business Revenues

Revenues from unconsolidated joint business consists of (1) our share of pretax co-promotion profits in the U.S. (2) reimbursement of our selling and development expenses in the U.S.; and (3) revenue on sales of RITUXAN in the rest of world, which consist of our share of pretax co-promotion profits in Canada and royalty revenue on sales of RITUXAN outside the U.S. and Canada by Roche, and its sublicensees. Pre-tax co-promotion profits are calculated and paid to us by Genentech in the U.S. and by Roche in Canada. Pre-tax co-promotion profits consist of U.S. and Canadian sales of RITUXAN to third-party customers net of discounts and allowances less the cost to manufacture RITUXAN, third-party royalty expenses, distribution, selling, and marketing expenses, and joint development expenses incurred by Genentech, Roche and us. We record our share of the pretax co-promotion profits in Canada and royalty revenues on sales of RITUXAN outside the U.S. on a cash basis. Additionally, our share of the pretax co-promotion profits in the U.S. includes estimates supplied by Genentech. Actual results may ultimately differ from our estimates.

Revenues from unconsolidated joint business consist of the following:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Biogen Idec’s share of co-promotion profits in the U.S.	$	848.0	$	773.6	$	733.5
Reimbursement of selling and development expenses in the U.S.		58.3		65.6		59.7
Revenue on sales of RITUXAN outside the U.S.		170.9		255.7		335.0

Total unconsolidated joint business revenues	$	1,077.2	$	1,094.9	$	1,128.2

In 2010, 2009 and 2008, the 40% co-promotion profit-sharing threshold was met during the first quarter.

Currently, we record our share of the expenses incurred by the collaboration for the development of anti-CD20 products in research and development expense in our consolidated statements of income. We incurred $50.6 million, $62.5 million and $43.6 million in development expense for the years ended December 31, 2010, 2009, and 2008, respectively. After an anti-CD20 product is approved, we will record our share of the development expenses related to that product as a reduction of our share of pretax co-promotion profits in revenues from unconsolidated joint business. As a result of the October 2010 amendment of our collaboration agreement with Genentech, we are no longer responsible for any development costs for ocrelizumab.

Elan

We collaborate with Elan on the development, manufacture and commercialization of TYSABRI. Under the terms of our collaboration agreement, we manufacture TYSABRI and collaborate with Elan on the product’s marketing, commercial distribution and ongoing development activities. The agreement is designed to effect an equal sharing of profits and losses generated by the activities of our collaboration. Under the agreement, however, once sales of TYSABRI exceeded specific thresholds, Elan was required to make milestone payments to us in order to continue sharing equally in the collaboration’s results. As of December 31, 2010, Elan has made milestone payments to us of $75.0 million in the third quarter of 2008 and $50.0 million in the first quarter of 2009. These amounts were recorded as deferred revenue upon receipt and are recognized as revenue in our consolidated statements of income based on the ratio of units shipped in the current period over the total units expected to be shipped over the remaining term of the collaboration. No additional milestone payments are required under the agreement to maintain the current profit sharing split. The term of our collaboration agreement extends until November 2019. Each of Biogen Idec and Elan has the option to buy the other party’s rights to TYSABRI upon expiration of the term or if the other party undergoes a change of control (as defined in the collaboration agreement). In addition, each of Biogen Idec and Elan can terminate the agreement for convenience or material breach by the other party, in which case, among other things, certain licenses, regulatory approvals and other rights related to the manufacture, sale and development of TYSABRI are required to be transferred to the party that is not terminating for convenience or is not in material breach of the agreement.

In the U.S., we sell TYSABRI to Elan who sells the product to third party distributors. Our sales price to Elan in the U.S. is set prior to the beginning of each quarterly period to effect an approximate equal sharing of the gross margin between Elan and us. We recognize revenue for sales in the U.S. of TYSABRI upon Elan’s shipment of the product to the third party distributors, at which time all revenue recognition criteria have been met. As of December 31, 2010 and 2009, we had deferred revenue of $20.8 million and $23.6 million, respectively, for shipments to Elan that remained in Elan’s ending inventory pending shipment of the product to the third party distributors. We incur manufacturing and distribution costs, research and development expenses, commercial expenses, and general and administrative expenses related to TYSABRI. We record these expenses to their respective line items within our consolidated statements of income when they are incurred. Research and development and sales and marketing expenses are shared equally with Elan and the reimbursement of these expenses is recorded as reductions of the respective expense categories. During the years ended December 31, 2010, 2009 and 2008, we recorded $49.8 million, $25.3 million and $23.6 million, respectively, as reductions of research and development expense for reimbursements from Elan. In addition, for the years ended December 31, 2010, 2009 and 2008, we recorded $68.5 million, $62.5 million and $33.7 million, respectively, as reductions of selling, general and administrative expense for reimbursements from Elan.

In the rest of world, we are responsible for distributing TYSABRI to customers and are primarily responsible for all operating activities. Generally, we recognize revenue for sales of TYSABRI in the rest of world at the time of product delivery to our customers. Payments are made to Elan for their share of the rest of world net operating profits to effect an equal sharing of collaboration operating profit. These payments also include the reimbursement for our portion of third-party royalties that Elan pays on behalf of the collaboration relating to rest of world sales. As rest of world sales of TYSABRI increase, our collaboration profit sharing expense is expected to increase. These amounts are reflected in the collaboration profit sharing line in our consolidated statements of income. For the years ended December 31, 2010, 2009 and 2008, $258.1 million, $215.9 million and $136.0 million, respectively, was reflected in the collaboration profit sharing line for our collaboration with Elan.

Acorda

On June 30, 2009, we entered into a collaboration and license agreement with Acorda Therapeutics, Inc. (Acorda) to develop and commercialize products containing fampridine in markets outside the U.S. The transaction represents a sublicensing of an existing license agreement between Acorda and Elan. The parties have also entered into a related supply agreement. The $110.0 million upfront payment made on July 1, 2009 to Acorda was recorded as research and development expense during the second quarter 2009 as the product candidate had not received regulatory approval. Fampridine was approved in the U.S. on January 22, 2010 under the trade name AMPYRA (dalfampridine) Extended Release Tablets, 10mg. AMPYRA is indicated to improve walking in patients with MS. This was demonstrated by an increase in walking speed. Acorda is developing and marketing AMPYRA in the U.S.

Under the terms of the agreement, we will commercialize FAMPYRA and any aminopyridine products developed in our territory and will also have responsibility for regulatory activities and future clinical development of FAMPYRA in those markets. We may incur additional milestone payments of up to $400.0 million based upon the successful achievement of regulatory and commercial sales milestones. We will also make tiered royalty payments to Acorda on sales outside of the U.S.

Elan will continue to manufacture commercial supply of FAMPYRA based upon its existing supply agreement with Acorda. Under the existing agreements with Elan, Acorda will pay Elan 7% of the upfront and milestone payments that Acorda receives from us.

In January 2011, the EMA’s Committee for Medicinal Products for Human Use (CHMP) issued a negative opinion recommending against approval of FAMPYRA to improve walking ability in adult patients with multiple sclerosis in the European Union. We intend to appeal this opinion and request a re-examination of the decision by the CHMP. We also received a Notice of Deficiency from Health Canada for our application to sell FAMPYRA in Canada.

A summary of activity related to this collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Upfront and milestones payments made to Acorda	$	—	$	110.0	$	—
Total expense incurred by Biogen Idec excluding upfront and milestone payments	$	22.8	$	4.7	$	—
Total expense reflected within our consolidated statements of income	$	22.8	$	114.7	$	—

A summary of activity related to this collaboration since inception, along with an estimate of additional future development expense expected to be incurred by us, is as follows:


(In millions)	As of December 31, 2010

Total upfront and milestone payments made to Acorda	$	110.0
Total development expense incurred by Biogen Idec, excluding upfront and milestone payments	$	27.5
Estimate of additional amounts to be incurred by us in development of FAMPYRA	$	89.0

Swedish Orphan Biovitrum

We have a collaboration agreement with Swedish Orphan Biovitrum (Biovitrum) to jointly develop and commercialize long-lasting recombinant Factor VIII and Factor IX for the treatment of hemophilia. In February 2010, we restructured our collaboration agreement with Biovitrum and assumed full development responsibilities and costs, as well as manufacturing rights for the Factor VIII and Factor IX programs in exchange for increased marketing rights for rest of world territories which was previously shared between the two companies. These territories are in addition to our existing commercial rights in North America. Biovitrum will retain commercial rights in Europe, Russia, Turkey and the Middle East.

Amounts incurred by us in the development of long-lasting recombinant Factor VIII and Factor IX are reflected as research and development expense in our consolidated statements of income, reduced by amounts due from Biovitrum. A summary of collective activity related to these programs is as follows:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Total expense incurred by collaboration	$	78.9	$	44.9	$	33.7
Total expense reflected within our consolidated statements of income	$	78.5	$	22.5	$	18.8

A summary of activity related to this collaboration since inception, along with an estimate of additional future development expense expected to be incurred by us, is as follows:


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments received from Biovitrum	$	5.0
Total development expense incurred by Biogen Idec excluding upfront and milestone payments	$	133.1
Estimate of additional amounts to be incurred by us in development of Factors VIII and IX	$	314.3

Abbott Biotherapeutics Corp (formerly Facet Biotech)

We have a collaboration agreement with Abbott Biotherapeutics Corp (Abbott) aimed at advancing the development and commercialization of daclizumab in MS. Under the agreement, development and commercialization costs and profits are shared equally. We may incur up to an additional $180.0 million of payments upon achievement of development and commercial milestones.

In January 2010, we agreed with our collaborator, Abbott, to assume the manufacture of daclizumab and began the process of transferring from Abbott the manufacturing technology necessary for us to manufacture daclizumab.

A summary of activity related to this collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Total expense incurred by collaboration	$	74.8	$	40.8	$	65.7
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	37.4	$	20.4	$	32.8

A summary of activity related to this collaboration since inception, along with an estimate of additional future development expense expected to be incurred by us, is as follows:


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments made to Abbott	$	80.0
Total development expense incurred by Biogen Idec excluding upfront and milestone payments	$	159.9
Estimate of additional amounts to be incurred by us in development of current indications of daclizumab	$	456.0

UCB

In June 2009, UCB, S.A. (UCB) and we announced the discontinuation of a Phase 2 clinical trial of MS patients for this collaboration’s only product candidate due to the absence of clinically relevant efficacy. Since the inception of our collaboration agreement with UCB, we have incurred a total of $102.6 million in research and development expenses for this product candidate.

A summary of activity related to this collaboration is as follows:


	For the Years Ended
	December 31,
(In millions)	2010		2009		2008

Total expense incurred by collaboration	$	2.2	$	31.8	$	33.6
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	1.6	$	21.0	$	21.9

A summary of activity related to this collaboration since inception, along with an estimate of additional future development expense expected to be incurred by us, is as follows:


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments made to UCB	$	30.0
Total development expense incurred by Biogen Idec excluding upfront and milestone payments	$	72.6
Estimate of additional amounts to be incurred by us in development of the compound in this indication	$	—

Vernalis

We have a collaboration agreement with Vernalis plc (Vernalis) aimed at advancing the development and commercialization of an adenosine A2a receptor antagonist for treatment of Parkinson’s disease. Under the agreement, we received exclusive worldwide rights to develop and commercialize the compound. We are responsible for funding all development costs and may incur up to an additional $85.0 million of milestone payments upon achievement of certain objectives, as well as royalties on commercial sales.

A summary of activity related to this collaboration is as follows:


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Total expense incurred by collaboration and reflected within our consolidated statements of income	$	16.2	$	14.8	$	16.9

A summary of activity related to this collaboration since inception, along with an estimate of additional future development expense expected to be incurred by us, is as follows:


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments made to Vernalis	$	13.0
Total development expense incurred by Biogen Idec Inc., excluding upfront and milestone payments	$	85.9
Estimate of additional amounts to be incurred by us in development of the compound in this indication	$	323.5

As of December 31, 2010 and 2009, our investment in Vernalis had a fair value of approximately $0.2 million and $0.5 million, respectively.

Litigation

12 Months Ended

Dec. 31, 2010

Litigation [Abstract]

Litigation


20.	Litigation

In 2006, the Massachusetts Department of Revenue (DOR) issued a Notice of Assessment against BIMA for $38.9 million of corporate excise tax for 2002, which includes associated interest and penalties. The assessment asserts that the portion of sales attributable to Massachusetts (sales factor), the computation of BIMA’s research and development credits and certain deductions claimed by BIMA were not appropriate, resulting in unpaid taxes for 2002. On December 6, 2006, we filed an abatement application with the DOR seeking abatements for 2001, 2002 and 2003. The abatement application was denied on July 24, 2007. On July 25, 2007, we filed a petition with the Massachusetts Appellate Tax Board (the Massachusetts ATB) seeking, among other items, abatements of corporate excise tax for 2001, 2002 and 2003 and adjustments in certain credits and credit carry forwards for 2001, 2002 and 2003. Issues before the Board include the computation of BIMA’s sales factor for 2001, 2002 and 2003, computation of BIMA’s research credits for those same years, and the availability of deductions for certain expenses and partnership flow-through items. We anticipate that the hearing on our petition will take place in the second quarter of 2011.

On October 24, 2008, Hoechst GmbH filed with the ICC International Court of Arbitration (Paris) a request for arbitration against Genentech, relating to a terminated license agreement (the “Hoescht License”) between Hoechst’s predecessor and Genentech granting Genentech certain rights with respect to U.S. Patents 5,849,522 (’522 patent) and 6,218,140 (’140 patent) and related patents outside the U.S. Although we are not a party to the arbitration, any damages awarded to Hoechst based on U.S. net sales of RITUXAN may be a cost charged to our collaboration with Genentech. The license was entered as of January 1, 1991 and was terminated by Genentech on October 27, 2008. We understand that Hoechst seeks payment of royalties on sales of Genentech products, including RITUXAN, damages for breach of contract, and other relief. We estimate, based solely on our understanding of Hoechst’s claims and not on any evaluation of the merits of the claims, that royalties and interest, if awarded in connection with U.S. net sales of RITUXAN, could total $100 million based on the 0.5% royalty rate set forth in the agreement and historical RITUXAN net sales.

On October 27, 2008, Sanofi-Aventis Deutschland GmbH (Sanofi), successor to Hoescht, filed suit against Genentech and Biogen Idec in federal court in Texas (E.D. Tex.) (Texas Action) claiming that RITUXAN and certain other Genentech products infringe the ’522 patent and the ’140 patent. The patents are due to expire in December 2015. Sanofi seeks preliminary and permanent injunctions, compensatory and exemplary damages, and other relief. The same day Genentech and Biogen Idec filed a complaint against Sanofi in federal court in California (N.D. Cal.) (California Action) seeking a declaratory judgment that RITUXAN and other Genentech products do not infringe the ’522 patent or the ’140 patent and a declaratory judgment that those patents are invalid. The Texas Action was ordered transferred to the federal court in the Northern District of California and consolidated with the California Action and we refer to the two actions together as the Consolidated Actions. We have not formed an opinion that an unfavorable outcome in the Consolidated Actions is either “probable” or “remote.” We believe that we have good and valid defenses and are vigorously defending against the allegations. In the event that we and Genentech are found liable we estimate that the range of any potential loss could extend to a royalty of up to 0.5% of net sales of RITUXAN, based on, among other things, the royalty rate set forth in the terminated Hoescht License and an analysis of royalty rates charged for comparable technologies. We believe that Sanofi would seek a substantially higher royalty rate, and we will continue to vigorously oppose its claims and position. One of the issues to be resolved in the California Action is whether any award of reasonable royalty damages would begin running from October 27, 2008, when Genentech terminated the Hoescht License, or from October 27, 2002, six years before Sanofi filed the Texas Action, the statutory limitations period for damages in patent cases. In the event that Genentech is ordered in the arbitration described above to pay royalties on RITUXAN sales under the Hoescht License up to the date of the termination of the Hoescht License (October 27, 2008), we do not anticipate that either we or Genentech would be subject to any damages award in the California Action for any period before October 27, 2008. Any damages awarded to Sanofi based on U.S. net sales of RITUXAN may be a cost charged to our collaboration with Genentech.

On September 15, 2009, we were issued U.S. patent No. 7,588,755 (’755 Patent), which claims the use of beta interferon for immunomodulation or treating a viral condition, viral disease, cancers or tumors. This patent, which expires in September 2026, covers, among other things, the treatment of MS with our product AVONEX. On May 27, 2010, Bayer Healthcare Pharmaceuticals Inc. (Bayer) filed a lawsuit against us in federal court in the District of New Jersey seeking a declaratory judgment of patent invalidity and noninfringement and seeking monetary relief in the form of attorneys’ fees, costs and expenses. On May 28, 2010, BIMA filed a lawsuit in federal court in the District of New Jersey alleging infringement of the ’755 Patent by EMD Serono, Inc. (manufacturer, marketer and seller of REBIF), Pfizer, Inc. (co-marketer of REBIF), Bayer (manufacturer, marketer and seller of BETASERON and manufacturer of EXTAVIA), and Novartis Pharmaceuticals Corp. (marketer and seller of EXTAVIA) and seeking monetary damages, including lost profits and royalties. The court has consolidated the two lawsuits. On August 16, 2010, BIMA amended its complaint to add Ares Trading S.A. (Ares), an affiliate of EMD Serono, as a defendant, and to seek a declaratory judgment that a purported “nonsuit and option agreement” between Ares and BIMA dated October 12, 2000, that purports to provide that Ares will have an option to obtain a license to the ’755 Patent, is not a valid and enforceable agreement or, alternatively, has been revoked and/or terminated by the actions of Ares or its affiliates. Ares has answered the amended complaint and has moved to compel arbitration of the claims against it, which we have opposed, and Ares’ motion is pending. Bayer, Pfizer, Novartis and EMD Serono have all filed counterclaims seeking declaratory judgments of patent invalidity and noninfringement, and seeking monetary relief in the form of costs and attorneys’ fees, and EMD Serono has filed a counterclaim seeking a declaratory judgment that the ’755 Patent is unenforceable based on alleged inequitable conduct.

On March 23, 2010, we and Genentech were issued U.S. Patent No. 7,682,612 (’612 patent) relating to a method of treating CLL using an anti-CD20 antibody. The patent which expires in November 2019 covers, among other things, the treatment of CLL with RITUXAN. On March 23, 2010, we filed a lawsuit in federal court in the Southern District of California against Glaxo Group Limited and GlaxoSmithKline LLC (collectively, GSK) alleging infringement of that patent based upon GSK’s manufacture, marketing and sale, offer to sell, and importation of ARZERRA. We seek damages, including a royalty and lost profits, and injunctive relief. GSK has filed a counterclaim seeking a declaratory judgment of patent invalidity, noninfringement, unenforceability, and inequitable conduct, and seeking monetary relief in the form of costs and attorneys’ fees.

On January 26, 2011, Novartis Vaccines and Diagnostics, Inc. (Novartis V&D) filed suit against us in federal district court in Delaware, alleging that TYSABRI infringes U.S. Patent No. 5,688,688 (“Vector for Expression of a Polypeptide in a Mammalian Cell”), which was granted in November 1997 and expires in November 2014. Novartis V&D seeks a declaration of infringement, a finding of willful infringement, compensatory damages, treble damages, interest, costs and attorneys’ fees. We have not formed an opinion that an unfavorable outcome is either “probable” or “remote”, and do not express an opinion at this time as to the likely outcome or the magnitude or range of any potential loss. We believe that we have good and valid defenses to the complaint and will vigorously defend against it.

We are also involved in product liability claims and other legal proceedings generally incidental to our normal business activities. While the outcome of any of these proceedings cannot be accurately predicted, we do not believe the ultimate resolution of any of these existing matters would have a material adverse effect on our business or financial conditions.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2010

Commitments and Contingencies [Abstract]

Commitments and Contingencies


21.	Commitments and Contingencies

Leases

We rent laboratory and office space and certain equipment under non-cancelable operating leases. These lease agreements contain various clauses for renewal at our option and, in certain cases, escalation clauses typically linked to rates of inflation. In addition to rent, the leases may require us to pay additional amounts for taxes, insurance, maintenance and other operating expenses. Amounts reflected within the table below details future minimum rental commitments under non-cancelable operating leases as of December 31 for each of the years presented. Rental expense under these leases, which terminate at various dates through 2025, amounted to $44.8 million in 2010, $36.4 million in 2009 and $36.0 million in 2008.

As of December 31, 2010, minimum rental commitments under non-cancelable leases, net of income from subleases, for each of the next five years and total thereafter were as follows:


(In millions)	2011			2012			2013			2014			2015		Thereafter		Total

Minimum lease payments	$	40.9		$	31.1		$	32.6		$	31.1		$	26.5	$	205.6	$	367.8
Less: income from subleases		(0.4	)		(0.4	)		(0.5	)		(0.4	)		—		—		(1.7	)

Net minimum lease payments	$	40.5		$	30.7		$	32.1		$	30.7		$	26.5	$	205.6	$	366.1

Financing Arrangement

As described in Note 10 Property, Plant & Equipment to these consolidated financial statements, on October 1, 2010, we sold the San Diego facility and agreed to lease back the facility for a period of 15 months. We have accounted for these transactions as a financing arrangement and recorded an obligation of $127.0 million on that date. As of December 31, 2010, our remaining obligation was $125.9 million, which is reflected as a component of current portion of notes payable, line of credit and other financing arrangements within our consolidated balance sheet.

Other Funding Commitments

As of December 31, 2010, we have funding commitments of up to approximately $19.0 million as part of our investment in biotechnology oriented venture capital funds.

As of December 31, 2010, we have several ongoing clinical studies in various clinical trial stages. Our most significant clinical trial expenditures are to clinical research organizations (CROs). The contracts with CROs are generally cancellable, with notice, at our option. We have recorded accrued expenses of $16.1 million on our consolidated balance sheet for expenditures incurred by CROs as of December 31, 2010. We have approximately $326.9 million in cancellable future commitments based on existing CRO contracts as of December 31, 2010.

Contingent Milestone Payments

Based on our development plans as of December 31, 2010, we have committed to make potential future milestone payments to third parties of up to approximately $1,334.3 million as part of our various collaborations, including licensing and development programs. Payments under these agreements generally become due and payable only upon achievement of certain development, regulatory or commercial milestones. Because the achievement of these milestones had not occurred as of December 31, 2010, such contingencies have not been recorded in our financial statements.

Guarantees

12 Months Ended

Dec. 31, 2010

Guarantees [Abstract]

Guarantees


22.	Guarantees

As of December 31, 2010 and 2009, we did not have significant liabilities recorded for guarantees.

We enter into indemnification provisions under our agreements with other companies in the ordinary course of business, typically with business partners, contractors, clinical sites and customers. Under these provisions, we generally indemnify and hold harmless the indemnified party for losses suffered or incurred by the indemnified party as a result of our activities. These indemnification provisions generally survive termination of the underlying agreement. The maximum potential amount of future payments we could be required to make under these indemnification provisions is unlimited. However, to date we have not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. As a result, the estimated fair value of these agreements is minimal. Accordingly, we have no liabilities recorded for these agreements as of December 31, 2010 and 2009.

Employee Benefit Plans

12 Months Ended

Dec. 31, 2010

Employee Benefit Plans [Abstract]

Employee Benefit Plans


23.	Employee Benefit Plans

401(k) Savings Plan

We maintain a 401(k) Savings Plan which is available to substantially all regular employees in the U.S. over the age of 21. Participants may make voluntary contributions. We make matching contributions according to the 401(k) Savings Plan’s matching formula. Beginning in January 2008, all past and current matching contributions will vest immediately. Previously, the matching contributions vested over four years of service by the employee. Participant contributions vest immediately. The 401(k) Savings Plan also holds certain transition contributions on behalf of participants who previously participated in the Biogen, Inc. Retirement Plan. The expense related to our 401(k) Savings Plan primarily consists of our matching contributions.

Expense related to our 401(k) Savings Plan totaled $26.3 million, $27.9 million and $22.8 million for the years ended December 31, 2010, 2009 and 2008, respectively.

Deferred Compensation Plan

We maintain a non-qualified deferred compensation plan, known as the Supplemental Savings Plan (SSP), which allows a select group of management employees in the U.S. to defer a portion of their compensation. The SSP also provides certain credits to highly compensated U.S. employees, which are paid by the company. These credits are known as the Restoration Match. The deferred compensation amounts are accrued when earned. Such deferred compensation is distributable in cash in accordance with the rules of the SSP. Deferred compensation amounts under such plan as of December 31, 2010 and 2009 totaled approximately $62.2 million and $63.6 million, respectively, and are included in other long-term liabilities within the accompanying consolidated balance sheets. The SSP also holds certain transition contributions on behalf of participants who previously participated in the Biogen, Inc. Retirement Plan. Beginning in 2008, the Restoration Match vests immediately. Previously, the Restoration Match and transition contributions vested over four and seven years of service, respectively, by the employee. Participant contributions vest immediately. Distributions to participants can be either in one lump sum payment or annual installments as elected by the participants.

Pension Plan

We currently maintain retiree benefit plans which include, a defined benefit plan for employees in our German affiliate and other insignificant defined benefit plans in certain other countries in which we have an operating presence.

The obligations under the German plan totaled $8.2 million and $5.7 million as of December 31, 2010 and 2009, respectively. Net periodic pension cost relate to the German plan totaled $1.1 million, $1.1 million and $1.0 million for the years ended December 31, 2010, 2009 and 2008, respectively.

Segment Information

12 Months Ended

Dec. 31, 2010

Segment Information [Abstract]

Segment Information


24.	Segment Information

We operate as one business segment, which is the business of discovering, developing, manufacturing and marketing products for the treatment of serious diseases with a focus on neurological disorders and therefore, our chief operating decision-maker manages the operations of our Company as a single operating segment. Enterprise-wide disclosures about product revenues, other revenues and long-lived assets by geographic area and information relating to major customers are presented below. Revenues are primarily attributed to individual countries based on location of the customer or licensee.

Revenue by product is summarized as follows:


	For the Years Ended December 31,
	2010						2009						2008
	United		Rest of				United		Rest of				United		Rest of
(In millions)	States		World		Total		States		World		Total		States		World		Total

AVONEX	$	1,491.6	$	1,026.8	$	2,518.4	$	1,406.2	$	916.7	$	2,322.9	$	1,276.5	$	926.1	$	2,202.6
TYSABRI		252.8		647.4		900.2		231.8		544.2		776.0		196.4		392.2		588.6
Other		—		51.5		51.5		—		54.0		54.0		—		48.5		48.5

Total product revenues	$	1,744.4	$	1,725.7	$	3,470.1	$	1,638.0	$	1,514.9	$	3,152.9	$	1,472.9	$	1,366.8	$	2,839.7

Geographic Information

The following tables contain certain financial information by geographic area:


December 31, 2010 (In millions)	U.S.		Europe		Germany		Asia		Other		Total

Product revenues from external customers	$	1,744.4	$	1,090.7	$	362.4	$	69.0	$	203.6	$	3,470.1
Revenues from unconsolidated joint business	$	906.3	$	95.3	$	—	$	26.0	$	49.6	$	1,077.2
Other revenues from external customers	$	136.0	$	32.6	$	0.5	$	—	$	—	$	169.1
Long-lived assets	$	1,100.3	$	717.4	$	1.5	$	5.4	$	1.6	$	1,826.2


December 31, 2009 (In millions)	U.S.		Europe		Germany		Asia		Other		Total

Product revenues from external customers	$	1,638.0	$	913.7	$	374.8	$	47.9	$	178.5	$	3,152.9
Revenues from unconsolidated joint business	$	839.2	$	190.2	$	—	$	24.1	$	41.4	$	1,094.9
Other revenues from external customers	$	102.8	$	26.2	$	0.5	$	—	$	—	$	129.5
Long-lived assets	$	1,092.7	$	705.6	$	1.4	$	3.6	$	2.1	$	1,805.4


December 31, 2008 (In millions)	U.S.		Europe		Germany		Asia		Other		Total

Product revenues from external customers	$	1,472.9	$	822.6	$	354.5	$	36.5	$	153.2	$	2,839.7
Revenues from unconsolidated joint business	$	793.2	$	272.3	$	—	$	21.7	$	41.0	$	1,128.2
Other revenues from external customers	$	96.5	$	32.8	$	0.3	$	—	$	—	$	129.6
Long-lived assets	$	1,111.2	$	658.8	$	2.5	$	4.2	$	1.2	$	1,777.9

Revenues from Unconsolidated Joint Business

Approximately 23%, 25% and 28% of our total revenues in 2010, 2009 and 2008, respectively, are derived from our joint business arrangement with Genentech. For a more detailed discussion of our collaboration with Genentech, please read Note 19, Collaborations to these consolidated financial statements.

Significant Customers

We recorded revenue from two wholesale distributors accounting for 18% and 11% of gross product revenue in 2010, 18% and 12% of gross product revenues in 2009, and 16% and 13% of gross product revenues in 2008.

Other

As of December 31, 2010, 2009 and 2008, approximately $644.7 million, $665.8 million and $611.5 million, respectively, of our long-lived assets were related to our manufacturing facilities in Denmark.

Quarterly Financial Data (Unaudited)

12 Months Ended

Dec. 31, 2010

Quarterly Financial Data (Unaudited) [Abstract]

Quarterly Financial Data (Unaudited)


25.	Quarterly Financial Data (Unaudited)


									Fourth
	First			Second		Third			Quarter			Total
(In millions, except per share amounts)	Quarter(a)			Quarter		Quarter(b)			(c)(d)			Year

2010
Product revenues	$	824.2		$	859.2	$	876.9		$	909.8		$	3,470.1
Unconsolidated joint business revenues	$	254.9		$	306.4	$	258.0		$	258.0		$	1,077.3
Other revenues	$	29.7		$	47.1	$	41.0		$	51.4		$	169.1
Total revenues	$	1,108.9		$	1,212.7	$	1,175.8		$	1,219.0		$	4,716.4
Gross Profit	$	1,011.8		$	1,105.7	$	1,079.9		$	1,118.8		$	4,316.2
Total cost and expenses and income tax expense	$	880.5		$	919.1	$	1,056.7		$	942.6		$	3,798.9
Other income (expense), net	$	(8.4	)	$	1.0	$	(6.9	)	$	(4.7	)	$	(19.0	)
Net income	$	220.0		$	294.6	$	112.2		$	271.8		$	898.6
Net income attributable to noncontrolling interest, net of tax	$	2.6		$	1.2	$	(141.9	)	$	31.5		$	(106.7	)
Net income (loss) attributable to Biogen Idec Inc.	$	217.4		$	293.4	$	254.1		$	240.3		$	1,005.3
Basic earnings per share attributable to Biogen Idec Inc	$	0.80		$	1.13	$	1.06		$	1.00		$	3.98
Diluted earnings per share attributable to Biogen Idec Inc	$	0.80		$	1.12	$	1.05		$	0.99		$	3.94


	First		Second		Third		Fourth		Total
(In millions, except per share amounts)	Quarter(e)		Quarter(f)		Quarter		Quarter(g)		Year

2009
Product revenues	$	733.4	$	791.0	$	801.7	$	826.8	$	3,152.9
Unconsolidated joint business revenues	$	278.8	$	275.6	$	283.9	$	256.6	$	1,094.9
Other revenues	$	24.3	$	26.7	$	34.9	$	43.6	$	129.5
Total revenues	$	1,036.5	$	1,093.3	$	1,120.5	$	1,127.0	$	4,377.3
Gross Profit	$	938.3	$	1,002.6	$	1,027.0	$	1,027.3	$	3,995.2
Total cost and expenses and income tax expense	$	796.8	$	963.1	$	850.3	$	827.4	$	3,437.5
Other income (expense), net	$	6.8	$	14.7	$	9.4	$	6.4	$	37.3
Net income	$	246.6	$	144.9	$	279.6	$	306.0	$	977.1
Net income attributable to noncontrolling interest, net of tax	$	2.6	$	2.0	$	1.9	$	0.4	$	6.9
Net income attributable to Biogen Idec Inc.	$	244.0	$	142.8	$	277.7	$	305.6	$	970.1
Basic earnings per share attributable to Biogen Idec Inc	$	0.85	$	0.49	$	0.96	$	1.07	$	3.37
Diluted earnings per share attributable to Biogen Idec Inc	$	0.84	$	0.49	$	0.95	$	1.06	$	3.35

Full year amounts may not sum due to rounding.


(a)		Included within total cost and expenses and income tax expense for the first quarter of 2010 is a charge to acquired IPR&D of $40.0 million related to the achievement of a milestone by Biogen Idec Hemophilia, Inc. (formerly Syntonix Pharmaceuticals, Inc.).

(b)		Included within total cost and expenses and income tax expense for the third quarter of 2010 is a charge to acquired IPR&D of $205.0 million incurred in connection with the license agreement entered into with Knopp Neurosciences Inc. (Knopp), which we consolidated as we determined that we are the primary beneficiary of the entity. The $205.0 million charge was partially offset by an attribution of $145.0 million to the noncontrolling interest.

(c)		Net income attributable to noncontrolling interest in the fourth quarter of 2010 includes a charge of $25.0 million related to the payment made in 2010 to Cardiokine Biopharma, LLC pursuant to the termination of our lixivaptan collaboration.

(d)		Included in total cost and expenses and income tax expense for the fourth quarter of 2010 are charges totaling $75.2 million related to our restructuring plan announced November 3, 2010.

(e)		Changes in tax law in certain state jurisdictions in which we operate during the first quarter of 2009 resulted in a $30.2 million reduction to our first quarter 2009 income tax expense.

(f)		Included within total cost and expenses and income tax expense for the second quarter of 2009 is the $110.0 million upfront payment made to Acorda Therapeutics, Inc. pursuant to our June 30, 2009 collaboration and license agreement to develop and commercialize products containing fampridine in markets outside the U.S.

(g)		Resolution of federal, state and foreign tax audits, including the effective settlement of several uncertain tax positions during the fourth quarter of 2009 resulted in a $34.0 million reduction to our fourth quarter 2009 income tax expense.

Subsequent Events

12 Months Ended

Dec. 31, 2010

Subsequent Events [Abstract]

Subsequent Events


26.	Subsequent Events

We did not have any material recognizable subsequent events. However, we did have the following nonrecognizable subsequent events:


	•	On January 26, 2011, Novartis Vaccines and Diagnostics, Inc. filed suit against us alleging that TYSABRI infringes U.S. Patent No. 5,688,688. For information about legal proceedings related to this matter please read Note 20, Litigation to these consolidated financial statements.

	•	On January 31, 2011, we entered into an agreement to terminate our 15 month lease of the San Diego facility. Under the terms of this agreement, we will continue to make monthly rental payments through August 31, 2011 and will have no continuing involvement or remaining obligation after that date. For additional information related to our lease of the San Diego facility please read Note 10, Property, Plant and Equipment to these consolidated financial statements.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2010

Summary of Significant Accounting Policies (Policies) [Abstract]

Product Revenues

Reserves for Discounts and Allowances

Product revenue reserves are categorized as follows: discounts, contractual adjustments and returns.

Contractual adjustment reserves primarily relate to Medicaid and managed care rebates, VA and PHS discounts and other applicable allowances.


	•	Medicaid rebate reserves relate to our estimated obligations to states under established reimbursement arrangements. Rebate accruals are recorded in the same period the related revenue is recognized resulting in a reduction of product revenue and the establishment of a liability which is included in other current liabilities. Our liability for Medicaid rebates consists of estimates for claims that a state will make for the current quarter, claims for prior quarters that have been estimated for which an invoice has not been received, invoices received for claims from the prior quarters that have not been paid and an estimate of potential claims that will be made for inventory that exists in the distribution channel at period end.

	•	VA rebates or chargeback reserves represent our estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices we charge to wholesalers which provide those products. The wholesaler charges us for the difference between what the wholesaler pays for the products and the ultimate selling price to the qualified healthcare providers. Rebate and chargeback reserves are established in the same period as the related revenue is recognized resulting in a reduction in product revenue and accounts receivable. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider from the wholesaler, and we generally issue credits for such amounts within a few weeks of the wholesaler notifying us about the resale. Our reserves for VA and chargebacks consists of amounts that we expect to issue for inventory that exists at the wholesalers that we expect will be sold to qualified healthcare providers and chargebacks that wholesalers have claimed for which we have not issued a credit.


	•	Managed care rebate reserves represent our estimated obligations to third parties, primarily pharmacy benefit managers. Rebate accruals are recorded in the same period the related revenue is recognized resulting in a reduction of product revenue and the establishment of a liability which is included in accrued expenses and other current liabilities. These rebates result from performance-based goals that are primarily based on attaining contractually specified sales volumes and growth. The calculation of the accrual for these rebates is based on an estimate of the customer’s buying patterns and the resulting applicable contractual rebate rate(s) to be earned over a contractual period.

Revenues from Unconsolidated Joint Business

Royalty Revenues

Milestone Revenues

Multiple-Deliverable Revenue Arrangements

Fair Value Measurements


	•	Level 1 — Fair values are determined utilizing quoted prices (unadjusted) in active markets for identical assets or liabilities that we have the ability to access;

	•	Level 2 — Fair values are determined by utilizing quoted prices for identical or similar assets and liabilities in active markets or other market observable inputs such as interest rates, yield curves and foreign currency spot rates; and

	•	Level 3 — Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable.

Cash and Cash Equivalents

Accounts Receivable

Concentration of Credit Risk

As of December 31, 2010 and 2009, one wholesale distributor accounted for approximately 11.5% and 8.1% of consolidated receivables, respectively.

Inventory

Capitalization of Inventory Costs

Obsolescence and Unmarketable Inventory

Marketable Securities and Other Investments

Marketable Debt Securities

Strategic Investments

Non-Marketable Equity Securities

Evaluating Investments for Other-than-Temporary Impairments

Property, Plant and Equipment


Asset Category		Useful Lives

Land		Not depreciated
Buildings		15 to 40 years
Leasehold Improvements		Lesser of the useful life or the term of the respective lease
Furniture and Fixtures		7 years
Machinery and Equipment		6 to 15 years
Computer Software and Hardware		3 to 5 years

Intangible Assets

Impairment of Long-Lived Assets


	•	a significant decline in the observable market value of an asset;

	•	a significant change in the extent or manner in which an asset is used; or

	•	a significant adverse change that would indicate that the carrying amount of an asset or group of assets is not recoverable.

Goodwill

Acquired In-Process Research and Development (IPR&D)

Valuation of Contingent Consideration Resulting from a Business Combination

Derivative Instruments and Hedging Activities

Translation of Foreign Currencies

Accounting for Share-based Compensation

Research and Development Expenses

Income Taxes

Contingencies

Restructuring Charges

Earnings per Share

New Accounting Pronouncements

Acquisitions (Tables)

12 Months Ended

Dec. 31, 2010

Acquisitions (Tables) [Abstract]

Purchase Price Allocation for the Acquisition


(In millions)


Cash portion of consideration	$	32.5
Contingent consideration	$	81.2

Total purchase price	$	113.7

We have allocated the purchase price to the following separately identifiable assets and liabilities assumed as of December 17, 2010:


(In millions)


In process research and development	$	110.9
Goodwill		25.6
Deferred tax liability		(23.7	)
Other, net		0.9

Total purchase price	$	113.7

Restructuring (Tables)

12 Months Ended

Dec. 31, 2010

Restructuring (Tables) [Abstract]

Restructuring Plan Cost


	For the Year Ended
(In millions)	December 31, 2010

Workforce reduction	$	67.2
Facility consolidation		8.0

Total restructuring charges	$	75.2


	Workforce			Facility
(In millions)	Reduction			Consolidation			Total

Reserves established	$	67.2		$	8.0		$	75.2
Amounts paid		(6.6	)		—			(6.6	)
Additional depreciation and other non-cash charges		—			(2.2	)		(2.2	)

Restructuring reserves at December 31, 2010	$	60.6		$	5.8		$	66.4

Revenue Reserves (Tables)

12 Months Ended

Dec. 31, 2010

Revenue Reserves (Tables) [Abstract]

Analysis of the amount of, and change in, product revenue reserves


				Contractual
(In millions)	Discounts			Adjustments			Returns			Total

2010
Beginning balance	$	13.9		$	70.3		$	18.9		$	103.1
Current provisions relating to sales in current year		80.6			285.0			16.1			381.7
Adjustments relating to prior years		(2.7	)		(2.4	)		(1.8	)		(6.9	)
Payments/returns relating to sales in current year		(68.7	)		(184.3	)		(0.8	)		(253.8	)
Payments/returns relating to sales in prior years		(9.2	)		(61.6	)		(11.3	)		(82.1	)

Ending balance	$	13.9		$	107.0		$	21.1		$	142.0


				Contractual
(In millions)	Discounts			Adjustments			Returns			Total

2009
Beginning balance	$	9.2		$	48.1		$	18.1		$	75.4
Current provisions relating to sales in current year		74.0			192.5			15.8			282.3
Adjustments relating to prior years		—			—			0.8			0.8
Payments/returns relating to sales in current year		(60.8	)		(124.4	)		(0.6	)		(185.8	)
Payments/returns relating to sales in prior years		(8.5	)		(45.9	)		(15.2	)		(69.6	)

Ending balance	$	13.9		$	70.3		$	18.9		$	103.1


				Contractual
(In millions)	Discounts			Adjustments			Returns			Total

2008
Beginning balance	$	6.4		$	33.1		$	20.4		$	59.9
Current provisions relating to sales in current year		67.1			150.6			14.7			232.4
Adjustments relating to prior years		—			(1.6	)		(2.5	)		(4.1	)
Payments/returns relating to sales in current year		(57.8	)		(101.2	)		(0.1	)		(159.1	)
Payments/returns relating to sales in prior years		(6.5	)		(32.8	)		(14.4	)		(53.7	)

Ending balance	$	9.2		$	48.1		$	18.1		$	75.4

Summary of total product revenue reserves included in consolidated balance sheets


	As of December 31,
(In millions)	2010		2009

Reduction of accounts receivable	$	36.7	$	43.3
Current liability		105.3		59.8

Total reserves	$	142.0	$	103.1

Inventory (Tables)

12 Months Ended

Dec. 31, 2010

Inventory (Tables) [Abstract]

Components of inventories


	As of December 31,
(In millions)	2010		2009

Raw materials	$	59.0	$	49.2
Work in process		142.2		174.0
Finished goods		87.9		70.8

Total inventory	$	289.1	$	294.0

Components of inventory by product


	As of December 31,
(In millions)	2010		2009

AVONEX	$	87.0	$	76.8
TYSABRI		117.0		144.0
Other		26.1		24.0

Total finished goods and work in process	$	230.1	$	244.8

Raw materials		59.0		49.2

Total inventory	$	289.1	$	294.0

Amounts written-down related to unmarketable inventory


	For the Years Ended
	December 31,
(In millions)	2010		2009		2008

Write-downs of unmarketable inventory	$	11.8	$	16.9	$	29.8

Intangible Assets and Goodwill (Tables)

12 Months Ended

Dec. 31, 2010

Intangible Assets and Goodwill (Tables) [Abstract]

Intangible assets


		As of December 31, 2010							As of December 31, 2009
	Estimated			Accumulated							Accumulated
(In millions)	Life	Cost		Amortization			Net		Cost		Amortization			Net

Intangible assets:
Out-licensed patents	12 years	$	578.0	$	(350.2	)	$	227.8	$	578.0	$	(306.0	)	$	272.0
Core developed technology	15-23 years		3,005.3		(1,636.9	)		1,368.4		3,005.3		(1,472.4	)		1,532.9
In process research and development	up to 15 years upon commercialization		110.9		—			110.9		—		—			—
Trademarks and tradenames	Indefinite		64.0		—			64.0		64.0		—			64.0
In-licensed patents	14 years		3.0		(1.3	)		1.7		3.0		(1.1	)		1.9
Assembled workforce	4 years		2.1		(2.1	)		—		2.1		(1.8	)		0.3
Distribution rights	2 years		12.7		(12.7	)		—		12.7		(12.7	)		—

Total intangible assets		$	3,776.0	$	(2,003.2	)	$	1,772.8	$	3,665.1	$	(1,794.0	)	$	1,871.1

Changes in goodwill


	As of December 31,
(In millions)	2010			2009

Goodwill:
Beginning balance	$	1,138.6		$	1,138.6
Goodwill acquired during the year		25.6			—
Other		(17.9	)		—

Ending balance	$	1,146.3		$	1,138.6

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2010

Fair Value Measurements (Tables) [Abstract]

Summary of Assets and Liabilities Recorded at Fair Value


			Quoted		Significant
			Prices		Other		Significant
	As of		in Active		Observable		Unobservable
	December 31,		Markets		Inputs		Inputs
(In millions)	2010		(Level 1)		(Level 2)		(Level 3)

Assets:
Cash equivalents	$	651.8	$	—	$	651.8	$	—
Marketable debt securities:
Corporate debt securities		313.0		—		313.0		—
Government securities		785.3		—		785.3		—
Mortgage and other asset backed securities		92.9		—		92.9		—
Strategic investments		44.8		44.8		—		—
Venture capital investments		20.8		—		—		20.8
Derivative contracts		1.3		—		1.3		—
Plan assets for deferred compensation		13.0		—		13.0		—

Total	$	1,922.9	$	44.8	$	1,857.3	$	20.8

Liabilities:
Derivative contracts	$	12.2	$	—	$	12.2	$	—
Contingent consideration (Note 2)		81.2		—		—		81.2

Total	$	93.4	$	—	$	12.2	$	81.2


			Quoted		Significant
			Prices		Other		Significant
	As of		in Active		Observable		Unobservable
	December 31,		Markets		Inputs		Inputs
(In millions)	2009		(Level 1)		(Level 2)		(Level 3)

Assets:
Cash equivalents	$	476.4	$	—	$	476.4	$	—
Marketable debt securities:
Corporate debt securities		504.1		—		504.1		—
Government securities		1,133.5		—		1,133.5		—
Mortgage and other asset backed securities		238.3		—		238.3		—
Strategic investments		5.9		5.9		—		—
Venture capital investments		21.9		—		—		21.9
Derivative contracts		15.8		—		15.8		—
Plan assets for deferred compensation		13.6		—		13.6		—

Total	$	2,409.5	$	5.9	$	2,381.7	$	21.9

Liabilities:
Derivative contracts		11.1		—		11.1		—

Total	$	11.1	$	—	$	11.1	$	—

Fair value of venture capital investments


	As of December 31,
(In millions)	2010			2009

Beginning balance	$	21.9		$	23.9
Total net unrealized gains (losses) included in earnings		(2.1	)		(3.6	)
Net purchases, issuances, and settlements		1.0			1.6

Ending balance	$	20.8		$	21.9

Summary of fair and carrying value of debt instruments


	As of December 31,
(In millions)	2010		2009

Credit line from Dompé	$	8.1	$	17.2
Notes payable to Fumedica		24.2		31.3
6.0% Senior Notes due 2013		485.5		475.7
6.875% Senior Notes due 2018		618.0		589.1

Total fair value	$	1,135.8	$	1,113.3

Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2010

Financial Instruments (Tables) [Abstract]

Marketable Securities including Strategic Investments


			Gross		Gross
	Fair		Unrealized		Unrealized			Amortized
As of December 31, 2010 (In millions):	Value		Gains		Losses			Cost

Available-for-sale
Corporate debt securities
Current	$	93.2	$	0.1	$	—		$	93.1
Non-current		219.8		2.1		(0.5	)		218.2
Government securities
Current		352.8		0.2		—			352.6
Non-current		432.5		0.6		(0.6	)		432.5
Mortgage and other asset backed securities
Current		2.1		—		—			2.1
Non-current		90.8		0.5		(0.2	)		90.5

Total available-for-sale securities	$	1,191.2	$	3.5	$	(1.3	)	$	1,189.0

Other Investments
Strategic investments, non-current	$	44.8	$	17.5	$	—		$	27.3


			Gross		Gross
	Fair		Unrealized		Unrealized			Amortized
As of December 31, 2009 (In millions):	Value		Gains		Losses			Cost

Available-for-sale
Corporate debt securities
Current	$	177.2	$	1.5	$	—		$	175.7
Non-current		326.9		5.7		(0.3	)		321.5
Government securities
Current		501.6		1.2		—			500.4
Non-current		631.9		4.1		(0.5	)		628.3
Mortgage and other asset backed securities
Current		3.0		0.1		—			2.9
Non-current		235.3		4.1		(0.5	)		231.7

Total available-for-sale securities	$	1,875.9	$	16.7	$	(1.3	)	$	1,860.5

Other Investments
Strategic investments, non-current	$	5.9	$	2.7	$	(0.3	)	$	3.5

Summary of Contractual Maturities: Available-for-Sale Securities


	As of December 31, 2010				As of December 31, 2009
	Estimated		Amortized		Estimated		Amortized
(In millions)	Fair Value		Cost		Fair Value		Cost

Due in one year or less	$	448.1	$	447.8	$	522.0	$	519.5
Due after one year through five years		664.1		662.4		1,143.7		1,133.4
Due after five years		79.0		78.8		210.2		207.6

Total available-for-sale securities	$	1,191.2	$	1,189.0	$	1,875.9	$	1,860.5

Proceeds from Marketable Securities, excluding Strategic Investments


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Proceeds from maturities and sales	$	2,668.7	$	3,319.0	$	2,941.1
Realized gains	$	18.8	$	19.8	$	15.9
Realized losses	$	2.5	$	4.0	$	17.0

Derivative Instruments (Tables)

12 Months Ended

Dec. 31, 2010

Derivative Instruments (Tables) [Abstract]

Foreign currency forward contracts that were entered into to hedge forecasted revenue


	Notional Amount
	As of December 31,
Foreign Currency: (In millions)	2010		2009

Euro	$	460.3	$	495.9
Canadian dollar		24.0		22.3
Swedish krona		9.9		—

Total foreign currency forward contracts	$	494.2	$	518.2

Summary of Derivatives designated as Hedging Instruments


		Fair Value
(In millions)	Balance Sheet Location	As of December 31, 2010

Foreign Currency Contracts
Asset derivatives	Other current assets	$	—
Liability derivatives	Accrued expenses and other	$	11.0


		Fair Value
(In millions)	Balance Sheet Location	As of December 31, 2009

Foreign Currency Contracts
Asset derivatives	Other current assets	$	10.8
Liability derivatives	Accrued expenses and other	$	9.8

Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income


	Amount					Amount
	Recognized in					Reclassified from
	Accumulated Other					Accumulated Other
	Comprehensive					Comprehensive
	Income (Loss)					Income (Loss)				Amount of
	on Derivative			Income Statement		into Income			Income Statement	Gain/(Loss)
	Gain/(Loss)			Location		Gain/(Loss)			Location	Recorded
For the Years Ended (In millions)	(Effective Portion)			(Effective Portion)		(Effective Portion)			(Ineffective Portion)	(Ineffective Portion)

December 31, 2010:
Foreign currency contracts	$	(11.0	)		Revenue	$	45.7		Other income (expense)	$	0.4
December 31, 2009:
Foreign currency contracts	$	1.2			Revenue	$	(49.7	)	Other income (expense)	$	(1.1	)
December 31, 2008:
Foreign currency contracts	$	(44.1	)		Revenue	$	(8.5	)	Other income (expense)	$	0.2
Interest rate swap	$	—			Interest expense	$	—		Interest expense	$	(8.9	)

Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2010

Property, Plant and Equipment (Tables) [Abstract]

Components of property, plant and equipment, net


	As of December 31,
(In millions)	2010			2009

Land	$	107.6		$	111.2
Buildings		670.2			669.7
Leasehold improvements		100.8			73.1
Machinery and equipment		576.0			534.0
Computer software and hardware		392.8			334.2
Furniture and fixtures		54.5			50.7
Construction in progress		506.9			506.7

Total cost		2,408.8			2,279.6

Less: accumulated depreciation		(767.2	)		(642.5	)

Total property, plant and equipment, net	$	1,641.6		$	1,637.1

Net carrying amounts of the major classes of assets


	As of
	December 31,
(In millions)	2010

Land	$	45.7
Buildings		73.0
Furniture and fixtures		2.1
Machinery and equipment		5.6

Total cost	$	126.4

Indebtedness (Tables)

12 Months Ended

Dec. 31, 2010

Indebtedness (Tables) [Abstract]

Summary of indebtedness


	As of December 31,
(In millions)	2010		2009

Current portion:
Note payable to Fumedica	$	3.3	$	11.2
Credit line from Dompé		8.0		8.6
Financing arrangement for the sale of the San Diego facility		125.9		—

Current portion of notes payable, line of credit and other financing arrangements	$	137.2	$	19.8

Non-current portion:
6.0% Senior notes due 2013	$	449.8	$	449.6
6.875% Senior notes due 2018		597.9		603.2
Note payable to Fumedica		18.7		18.8
Credit line from Dompé		—		8.6

Non-current portion of notes payable and line of credit	$	1,066.4	$	1,080.2

Total debt maturities


(In millions)	As of December 31, 2010

2011	$	11.4
2012		3.4
2013		453.4
2014		3.4
2015		3.4
2016 and thereafter		560.2

Total	$	1,035.2

Equity (Tables)

12 Months Ended

Dec. 31, 2010

Equity (Tables) [Abstract]

Summary of Preferred Stock


	As of December 31, 2010						As of December 31, 2009
(In thousands)	Authorized		Issued		Outstanding		Authorized		Issued		Outstanding

Series A		1,750		8		8		1,750		8		8
Series X junior participating		1,000		—		—		1,000		—		—
Undesignated		5,250		—		—		5,250		—		—

Total preferred stock		8,000		8		8		8,000		8		8

Summary of common Stock

As of December 31, 2010

As of December 31, 2009

(In thousands)

Authorized

Issued

Outstanding

Authorized

Issued

Outstanding

Common stock

1,000,000

248,200

240,538

1,000,000

288,494

274,855

Accumulated Other Comprehensive Income (Loss) (Tables)

12 Months Ended

Dec. 31, 2010

Accumulated Other Comprehensive Income (Loss) (Tables) [Abstract]

Accumulated Other Comprehensive Income (Loss)


	As of December 31,
(In millions)	2010			2009

Translation adjustments	$	(24.4	)	$	35.6
Unrealized gains (losses) on securites available for sale		12.4			11.3
Unrealized gains (losses) on foreign currency forward contracts		(9.8	)		1.5
Unfunded status of pension and postretirement benefit plans		0.2			2.1

Accumulated other comprehensive income (loss)	$	(21.6	)	$	50.5

Earnings per Share (Tables)

12 Months Ended

Dec. 31, 2010

Earnings per Share (Tables) [Abstract]

Basic and diluted earnings per share


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Numerator:
Net income attributable to Biogen Idec Inc.	$	1,005.3		$	970.1		$	783.2
Adjustment for net income allocable to preferred stock		(2.0	)		(1.7	)		(1.3	)

Net income used in calculating basic and diluted earnings per share	$	1,003.3		$	968.4		$	781.9

Denominator:
Weighted average number of common shares outstanding		252.3			287.4			292.3
Effect of dilutive securities:
Stock options and employee stock purchase plan		0.9			0.6			1.3
Restricted stock awards		—			—			0.1
Time-vested restricted stock units		1.6			1.4			1.3
Market stock units		0.1			—			—
Performance-vested restricted stock units settled in shares		—			0.1			—

Dilutive potential common shares		2.6			2.1			2.7

Shares used in calculating diluted earnings per share		254.9			289.5			295.0

Anti dilutive securities excluded from computation of basic and dilutive earnings per share


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Numerator:
Net income allocable to preferred stock	$	2.0	$	1.7	$	1.3
Denominator:
Stock options		4.6		8.5		6.9
Time-vested restricted stock units		0.1		2.1		1.5
Market stock units		—		—		—
Performance-vested restricted stock units		—		0.2		—
Convertible preferred stock		0.5		0.5		0.5

Total		5.2		11.3		8.9

Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2010

Share-Based Compensation (Tables) [Abstract]

Share-based compensation expense included in consolidated statements of income


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Research and development	$	62.7		$	60.8		$	59.9
Selling, general and administrative		123.6			106.4			93.8
Restructuring charges		6.8			—			—

Subtotal		193.1			167.2			153.7
Capitalized share-based compensation costs		(3.5	)		(6.3	)		(7.5	)

Share-based compensation expense included in total costs and expenses		189.6			160.9			146.2
Income tax effect		(60.3	)		(49.4	)		(45.4	)

Share-based compensation expense included in net income attributable to Biogen Idec Inc.	$	129.3		$	111.5		$	100.8

Summary of share-based compensation expense associated with different programs


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Stock options	$	26.1		$	21.6		$	20.0
Market stock units		10.0			—			—
Time-vested restricted stock units		129.4			133.7			125.6
Performance-vested restricted stock units settled in shares		5.3			4.6			1.1
Performance-vested restricted stock units settled in cash		15.0			—			—
Restricted stock awards		—			—			0.5
Employee stock purchase plan		7.3			7.3			6.5

Subtotal		193.1			167.2			153.7
Capitalized share-based compensation costs		(3.5	)		(6.3	)		(7.5	)

Share-based compensation expense included in total costs and expenses		189.6			160.9			146.2

Weighted-average assumptions to estimate the fair value of the stock option grants awarded


	For the Years Ended December 31,
	2010			2009			2008

Expected option life (in years)		4.5			4.7			5.1
Expected stock price volatility		30.8	%		39.3	%		34.4	%
Risk-free interest rate		2.0	%		1.9	%		2.4	%
Expected dividend yield		0.0	%		0.0	%		0.0	%
Per share grant-date fair value	$	16.52		$	18.00		$	20.85

Stock option activity


				Weighted
				Average
				Exercise
(In thousands, except weighted average exercise price)	Shares			Price

Outstanding at December 31, 2007		14,900		$	50.03

Granted		1,475		$	60.23
Exercised		(3,769	)	$	41.99
Cancelled		(506	)	$	55.70

Outstanding at December 31, 2008		12,100		$	53.53

Granted		1,031		$	49.96
Exercised		(637	)	$	40.16
Cancelled		(1,664	)	$	60.74

Outstanding at December 31, 2009		10,830		$	52.88

Granted		124		$	57.38
Exercised		(3,455	)	$	46.86
Cancelled		(332	)	$	61.96

Outstanding at December 31, 2010		7,167		$	55.43

Tax benefit and cash received from stock option


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Tax benefit realized for stock options	$	16.0	$	1.5	$	28.0
Cash received from the exercise of stock options	$	160.0	$	25.2	$	158.3

Assumptions used in valuation of market based stock units


Expected dividend yield		0%
Range of excepted stock price volatility		28.3% - 38.8%
Range of risk-free interest rates		0.3% - 2.0%
60 calendar day average stock price on grant date		$49.08 - $54.12

Time vested restricted stock units activity


				Weighted
				Average
				Grant Date
(In thousands, except weighted average grant date fair value)	Shares			Fair Value

Unvested at December 31, 2007		4,592		$	49.12

Granted		3,129		$	58.42
Vested		(1,645	)	$	47.93
Forfeited		(499	)	$	53.95

Unvested at December 31, 2008		5,577		$	54.26

Granted		2,674		$	48.93
Vested		(2,421	)	$	52.08
Forfeited		(445	)	$	53.02

Unvested at December 31, 2009		5,385		$	52.72

Granted		2,067		$	54.79
Vested		(2,829	)	$	53.39
Forfeited		(400	)	$	52.93

Unvested at December 31, 2010		4,223		$	53.26

Performance-vested restricted stock units (PVRSUs) activity


				Weighted
				Average
				Grant Date
(In thousands, except weighted average grant date fair value)	Shares			Fair Value

Unvested at December 31, 2007		120		$	51.55

Granted		—		$	—
Vested		(27	)	$	49.33
Forfeited		(3	)	$	49.33

Unvested at December 31, 2008		90		$	52.29

Granted		325		$	49.42
Vested		(30	)	$	52.29
Forfeited		(97	)	$	51.30

Unvested at December 31, 2009		288		$	49.39

Granted		4		$	53.64
Vested		(129	)	$	49.69
Forfeited		(9	)	$	49.56

Unvested at December 31, 2010		154		$	49.24

Shares issued under employee stock purchase plan


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Shares issued under ESPP		0.6		0.6		0.5
Cash received under ESPP	$	23.5	$	22.6	$	21.3

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2010

Income Taxes (Tables) [Abstract]

Income before income tax provision and the income tax expense


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Income before income taxes (benefit):
Domestic	$	846.4		$	1,073.8		$	829.2
Foreign		383.5			258.9			326.7

Total	$	1,229.9		$	1,332.7		$	1,155.9

Income tax expense (benefit):
Current
Federal	$	357.7		$	439.9		$	431.2
State		19.6			3.1			24.3
Foreign		35.4			50.0			49.8

Total	$	412.7		$	493.0		$	505.3

Deferred
Federal	$	(70.6	)	$	(94.8	)	$	(119.2	)
State		(6.6	)		(39.0	)		(20.0	)
Foreign		(4.2	)		(3.6	)		(0.3	)

Total	$	(81.4	)	$	(137.4	)	$	(139.5	)

Total income tax expense	$	331.3		$	355.6		$	365.8

Components of deferred tax assets and liabilities


	As of December 31,
(In millions)	2010			2009

Deferred tax assets
Tax credits	$	47.6		$	35.2
Inventory, other reserves and accruals		203.1			166.4
Capitalized costs		6.7			8.7
Intangibles, net		61.8			83.2
Net operating loss		35.3			30.5
Share-based compensation		64.4			60.8
Other		70.3			60.6
Valuation allowance		(10.8	)		—

Total deferred tax assets	$	478.4		$	445.4

Deferred tax liabilities
Purchased intangible assets	$	(446.1	)	$	(475.4	)
Unrealized gain on investments and cumulative translation adjustment		(6.6	)		(6.3	)
Depreciation, amortization and other		(114.4	)		(115.6	)

Total deferred tax liabilities	$	(567.1	)	$	(597.3	)

Reconciliation between the U.S. federal statutory tax rate and effective tax rate


	For the Years Ended December 31,
	2010			2009			2008

Statutory rate		35.0	%		35.0	%		35.0	%
State taxes		1.7			(0.1	)		1.6
Taxes on foreign earnings		(10.7	)		(5.0	)		(5.8	)
Credits and net operating loss utilization		(3.0	)		(3.8	)		(2.9	)
Purchased intangible assets		1.9			2.0			3.7
IPR&D		5.0			—			0.8
Permanent items		(2.0	)		(1.3	)		(0.9	)
Other		(1.0	)		(0.1	)		0.1

Effective tax rate		26.9	%		26.7	%		31.6	%

Reconciliation of the beginning and ending amount of unrecognized tax benefits


(In millions)	2010			2009			2008

Balance at January 1,	$	147.1		$	249.6		$	221.1
Additions based on tax positions related to the current period		3.6			14.4			21.8
Additions for tax positions of prior periods		13.3			77.4			20.4
Reductions for tax positions of prior periods		(18.5	)		(88.7	)		(13.7	)
Statute expirations		(3.7	)		—			—
Settlements		(20.3	)		(105.6	)		—

Balance at December 31,	$	121.5		$	147.1		$	249.6

Other Consolidated Financial Statement Detail (Tables)

12 Months Ended

Dec. 31, 2010

Other Consolidated Financial Statement Detail (Tables) [Abstract]

Supplemental Cash Flow Information


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Cash paid during the year for:
Interest	$	68.1	$	68.1	$	40.0
Income taxes	$	394.7	$	745.4	$	372.0

Other income (expense), net


	For the Years Ended December 31,
(In millions)	2010			2009			2008

Interest income	$	22.3		$	48.5		$	72.1
Interest expense		(36.1	)		(35.8	)		(52.0	)
Impairments of investments		(21.3	)		(10.6	)		(60.3	)
Gain (loss) on sales of investments, net		16.3			22.8			(1.1	)
Foreign exchange gains (losses), net		(3.5	)		11.4			(9.8	)
Other, net		3.3			1.0			(6.6	)

Total other income (expense), net	$	(19.0	)	$	37.3		$	(57.7	)

Other Current Assets


	As of December 31,
(In millions)	2010		2009

Deferred tax assets	$	112.2	$	88.8
Prepaid taxes		31.4		11.0
Receivable from collaborations		7.3		5.3
Interest receivable		4.9		10.6
Other prepaid expenses		47.9		41.6
Other		12.1		20.6

Total other current assets	$	215.8	$	177.9

Accrued Expenses and Other


	As of December 31,
(In millions)	2010		2009

Employee compensation and benefits	$	159.7	$	127.1
Revenue-related rebates		90.1		52.0
Restructuring charges		66.4		—
Royalties and licensing fees		45.1		41.8
Deferred revenue		41.3		38.7
Collaboration expenses		31.6		35.7
Clinical development expenses		24.4		43.2
Interest payable		21.6		21.6
Construction in progress accrual		16.4		12.8
Current portion of contingent consideration		11.9		—
Other		157.4		127.9

Total accrued expense and other	$	665.9	$	500.8

Investments in Variable Interest Entities (Tables)

12 Months Ended

Dec. 31, 2010

Investments in Variable Interest Entities (Tables) [Abstract]

Summary of activity related to collaboration with Knopp


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Total upfront payments made to Knopp	$	26.4	$	—	$	—
Total development expense incurred by the collaboration excluding upfront and milestone payments	$	5.0	$	—	$	—
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	31.4	$	—	$	—
Collaboration expense attributed to noncontrolling interests, net of tax	$	—	$	—	$	—

Summary of activity related to collaboration with Neurimmune


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Milestone payments made to Neurimmune	$	—	$	7.5	$	10.5
Total development expense incurred by the collaboration, excluding upfront and milestone payments	$	15.5	$	9.0	$	5.9
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	15.5	$	16.5	$	16.4
Collaboration expense attributed to noncontrolling interests, net of tax	$	1.0	$	—	$	—

Summary of activity related to collaboration with Cardiokine


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Milestone payments made to Cardiokine	$	—	$	20.0	$	—
Total expense incurred by collaboration	$	51.1	$	66.5	$	50.5
Biogen Idec’s share of expense incurred by the collaboration reflected within our consolidated statements of income	$	46.0	$	79.8	$	45.5
Collaboration expense attributed to noncontrolling interests, net of tax	$	5.1	$	6.7	$	5.0

Summary of activity related to collaboration with Neurimmune, along with an estimate of additional future development


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments made to Neurimmune	$	20.0
Total development expense incurred by Biogen Idec excluding upfront and milestone payments	$	31.0
Estimate of additional amounts to be incurred by us in development of the lead compound	$	539.5

Collaborations (Tables)

12 Months Ended

Dec. 31, 2010

Collaborations (Tables) [Abstract]

Co-promotion profit sharing formula


				Before First New Product FDA Approval
	After First New			First Non-CLL GA101			GA101 CLL Sales
	Product FDA			FDA Approval Occurs			Trigger Occurs
Co-promotion Operating Profits†	Approval			First			First

I. First $50.0 million		30	%		30	%		30	%
II. Above $50.0 million		—			—			35	%
A. Until First GA101 Threshold Date		38	%		39	%		—
B. After First GA101 Threshold Date
1(a). Until First Threshold Date		37.5	%		—			—
1(b). After First Threshold Date and until Second Threshold Date		35	%		—			—
1(c). After Second Threshold Date		30	%		—			—
2. Until Second GA101 Threshold Date		—			37.5	%		—
C. After Second GA101 Threshold Date		—			35	%		—


†		First GA101 Threshold Date means the earlier of (1) the date of the First Non-CLL GA101 FDA Approval if U.S. gross sales of GA101 for the preceding consecutive 12 month period were at least $150.0 million or (2) the first day of the calendar quarter after the date of the First Non-CLL GA101 FDA Approval that U.S. gross sales of GA101 within any consecutive 12 month period have reached $150.0 million.

		Second GA101 Threshold Date means the first day of the calendar quarter after U.S. gross sales of GA101 within any consecutive 12 month period have reached $500.0 million.

		First Threshold Date means the earlier of (1) the GA101 CLL Sales Trigger, (2) the Second GA101 Threshold Date and (3) the later of (a) the first date that U.S. gross sales of New Products in any calendar year reach $150.0 million and (b) January 1 of the calendar year following the calendar year in which the First New Product FDA Approval occurs if gross sales of New Products reached $150.0 million within the same calendar year in which the First New Product FDA Approval occurred.

		Second Threshold Date means the later of (1) the first date that U.S. gross sales of New Products in any calendar year reach $350.0 million and (2) January 1 of the calendar year following the calendar year in which the First Threshold Date occurs.

Revenues from unconsolidated joint business


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Biogen Idec’s share of co-promotion profits in the U.S.	$	848.0	$	773.6	$	733.5
Reimbursement of selling and development expenses in the U.S.		58.3		65.6		59.7
Revenue on sales of RITUXAN outside the U.S.		170.9		255.7		335.0

Total unconsolidated joint business revenues	$	1,077.2	$	1,094.9	$	1,128.2

Summary of activity related to collaboration with Aroda


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Upfront and milestones payments made to Acorda	$	—	$	110.0	$	—
Total expense incurred by Biogen Idec excluding upfront and milestone payments	$	22.8	$	4.7	$	—
Total expense reflected within our consolidated statements of income	$	22.8	$	114.7	$	—

Summary of activity related to collaboration with Aroda, along with an estimate of additional future development expense


(In millions)	As of December 31, 2010

Total upfront and milestone payments made to Acorda	$	110.0
Total development expense incurred by Biogen Idec, excluding upfront and milestone payments	$	27.5
Estimate of additional amounts to be incurred by us in development of FAMPYRA	$	89.0

Summary of activity related to collaboration with Swedish Orphan Biovitrum


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Total expense incurred by collaboration	$	78.9	$	44.9	$	33.7
Total expense reflected within our consolidated statements of income	$	78.5	$	22.5	$	18.8

Summary of activity related to collaboration with Swedish Orphan Biovitrum, along with an estimate of additional future development expense


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments received from Biovitrum	$	5.0
Total development expense incurred by Biogen Idec excluding upfront and milestone payments	$	133.1
Estimate of additional amounts to be incurred by us in development of Factors VIII and IX	$	314.3

Summary of activity related to collaboration with Facet Biotech


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Total expense incurred by collaboration	$	74.8	$	40.8	$	65.7
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	37.4	$	20.4	$	32.8

Summary of activity related to collaboration with Facet Biotech, along with an estimate of additional future development expense


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments made to Abbott	$	80.0
Total development expense incurred by Biogen Idec excluding upfront and milestone payments	$	159.9
Estimate of additional amounts to be incurred by us in development of current indications of daclizumab	$	456.0

Summary of activity related to collaboration with UCB


	For the Years Ended
	December 31,
(In millions)	2010		2009		2008

Total expense incurred by collaboration	$	2.2	$	31.8	$	33.6
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	1.6	$	21.0	$	21.9

Summary of activity related to collaboration with UCB, along with an estimate of additional future development expense


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments made to UCB	$	30.0
Total development expense incurred by Biogen Idec excluding upfront and milestone payments	$	72.6
Estimate of additional amounts to be incurred by us in development of the compound in this indication	$	—

Summary of activity related to collaboration with Vernalis


	For the Years Ended December 31,
(In millions)	2010		2009		2008

Total expense incurred by collaboration and reflected within our consolidated statements of income	$	16.2	$	14.8	$	16.9

Summary of activity related to collaboration with Vernalis, along with an estimate of additional future development expense


	As of
	December 31,
(In millions)	2010

Total upfront and milestone payments made to Vernalis	$	13.0
Total development expense incurred by Biogen Idec Inc., excluding upfront and milestone payments	$	85.9
Estimate of additional amounts to be incurred by us in development of the compound in this indication	$	323.5

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2010

Commitments and Contingencies (Tables) [Abstract]

Minimum rental commitments under noncancellable leases


(In millions)	2011			2012			2013			2014			2015		Thereafter		Total

Minimum lease payments	$	40.9		$	31.1		$	32.6		$	31.1		$	26.5	$	205.6	$	367.8
Less: income from subleases		(0.4	)		(0.4	)		(0.5	)		(0.4	)		—		—		(1.7	)

Net minimum lease payments	$	40.5		$	30.7		$	32.1		$	30.7		$	26.5	$	205.6	$	366.1

Segment Information (Tables)

12 Months Ended

Dec. 31, 2010

Segment Information (Tables) [Abstract]

Revenue by product


	For the Years Ended December 31,
	2010						2009						2008
	United		Rest of				United		Rest of				United		Rest of
(In millions)	States		World		Total		States		World		Total		States		World		Total

AVONEX	$	1,491.6	$	1,026.8	$	2,518.4	$	1,406.2	$	916.7	$	2,322.9	$	1,276.5	$	926.1	$	2,202.6
TYSABRI		252.8		647.4		900.2		231.8		544.2		776.0		196.4		392.2		588.6
Other		—		51.5		51.5		—		54.0		54.0		—		48.5		48.5

Total product revenues	$	1,744.4	$	1,725.7	$	3,470.1	$	1,638.0	$	1,514.9	$	3,152.9	$	1,472.9	$	1,366.8	$	2,839.7

Geographic information


December 31, 2010 (In millions)	U.S.		Europe		Germany		Asia		Other		Total

Product revenues from external customers	$	1,744.4	$	1,090.7	$	362.4	$	69.0	$	203.6	$	3,470.1
Revenues from unconsolidated joint business	$	906.3	$	95.3	$	—	$	26.0	$	49.6	$	1,077.2
Other revenues from external customers	$	136.0	$	32.6	$	0.5	$	—	$	—	$	169.1
Long-lived assets	$	1,100.3	$	717.4	$	1.5	$	5.4	$	1.6	$	1,826.2


December 31, 2009 (In millions)	U.S.		Europe		Germany		Asia		Other		Total

Product revenues from external customers	$	1,638.0	$	913.7	$	374.8	$	47.9	$	178.5	$	3,152.9
Revenues from unconsolidated joint business	$	839.2	$	190.2	$	—	$	24.1	$	41.4	$	1,094.9
Other revenues from external customers	$	102.8	$	26.2	$	0.5	$	—	$	—	$	129.5
Long-lived assets	$	1,092.7	$	705.6	$	1.4	$	3.6	$	2.1	$	1,805.4


December 31, 2008 (In millions)	U.S.		Europe		Germany		Asia		Other		Total

Product revenues from external customers	$	1,472.9	$	822.6	$	354.5	$	36.5	$	153.2	$	2,839.7
Revenues from unconsolidated joint business	$	793.2	$	272.3	$	—	$	21.7	$	41.0	$	1,128.2
Other revenues from external customers	$	96.5	$	32.8	$	0.3	$	—	$	—	$	129.6
Long-lived assets	$	1,111.2	$	658.8	$	2.5	$	4.2	$	1.2	$	1,777.9

Quarterly Financial Data (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2010

Quarterly Financial Data (Unaudited) (Tables) [Abstract]

Quarterly Financial Data (Unaudited)


									Fourth
	First			Second		Third			Quarter			Total
(In millions, except per share amounts)	Quarter(a)			Quarter		Quarter(b)			(c)(d)			Year

2010
Product revenues	$	824.2		$	859.2	$	876.9		$	909.8		$	3,470.1
Unconsolidated joint business revenues	$	254.9		$	306.4	$	258.0		$	258.0		$	1,077.3
Other revenues	$	29.7		$	47.1	$	41.0		$	51.4		$	169.1
Total revenues	$	1,108.9		$	1,212.7	$	1,175.8		$	1,219.0		$	4,716.4
Gross Profit	$	1,011.8		$	1,105.7	$	1,079.9		$	1,118.8		$	4,316.2
Total cost and expenses and income tax expense	$	880.5		$	919.1	$	1,056.7		$	942.6		$	3,798.9
Other income (expense), net	$	(8.4	)	$	1.0	$	(6.9	)	$	(4.7	)	$	(19.0	)
Net income	$	220.0		$	294.6	$	112.2		$	271.8		$	898.6
Net income attributable to noncontrolling interest, net of tax	$	2.6		$	1.2	$	(141.9	)	$	31.5		$	(106.7	)
Net income (loss) attributable to Biogen Idec Inc.	$	217.4		$	293.4	$	254.1		$	240.3		$	1,005.3
Basic earnings per share attributable to Biogen Idec Inc	$	0.80		$	1.13	$	1.06		$	1.00		$	3.98
Diluted earnings per share attributable to Biogen Idec Inc	$	0.80		$	1.12	$	1.05		$	0.99		$	3.94


	First		Second		Third		Fourth		Total
(In millions, except per share amounts)	Quarter(e)		Quarter(f)		Quarter		Quarter(g)		Year

2009
Product revenues	$	733.4	$	791.0	$	801.7	$	826.8	$	3,152.9
Unconsolidated joint business revenues	$	278.8	$	275.6	$	283.9	$	256.6	$	1,094.9
Other revenues	$	24.3	$	26.7	$	34.9	$	43.6	$	129.5
Total revenues	$	1,036.5	$	1,093.3	$	1,120.5	$	1,127.0	$	4,377.3
Gross Profit	$	938.3	$	1,002.6	$	1,027.0	$	1,027.3	$	3,995.2
Total cost and expenses and income tax expense	$	796.8	$	963.1	$	850.3	$	827.4	$	3,437.5
Other income (expense), net	$	6.8	$	14.7	$	9.4	$	6.4	$	37.3
Net income	$	246.6	$	144.9	$	279.6	$	306.0	$	977.1
Net income attributable to noncontrolling interest, net of tax	$	2.6	$	2.0	$	1.9	$	0.4	$	6.9
Net income attributable to Biogen Idec Inc.	$	244.0	$	142.8	$	277.7	$	305.6	$	970.1
Basic earnings per share attributable to Biogen Idec Inc	$	0.85	$	0.49	$	0.96	$	1.07	$	3.37
Diluted earnings per share attributable to Biogen Idec Inc	$	0.84	$	0.49	$	0.95	$	1.06	$	3.35

Full year amounts may not sum due to rounding.


(a)		Included within total cost and expenses and income tax expense for the first quarter of 2010 is a charge to acquired IPR&D of $40.0 million related to the achievement of a milestone by Biogen Idec Hemophilia, Inc. (formerly Syntonix Pharmaceuticals, Inc.).

(b)		Included within total cost and expenses and income tax expense for the third quarter of 2010 is a charge to acquired IPR&D of $205.0 million incurred in connection with the license agreement entered into with Knopp Neurosciences Inc. (Knopp), which we consolidated as we determined that we are the primary beneficiary of the entity. The $205.0 million charge was partially offset by an attribution of $145.0 million to the noncontrolling interest.

(c)		Net income attributable to noncontrolling interest in the fourth quarter of 2010 includes a charge of $25.0 million related to the payment made in 2010 to Cardiokine Biopharma, LLC pursuant to the termination of our lixivaptan collaboration.

(d)		Included in total cost and expenses and income tax expense for the fourth quarter of 2010 are charges totaling $75.2 million related to our restructuring plan announced November 3, 2010.

(e)		Changes in tax law in certain state jurisdictions in which we operate during the first quarter of 2009 resulted in a $30.2 million reduction to our first quarter 2009 income tax expense.

(f)		Included within total cost and expenses and income tax expense for the second quarter of 2009 is the $110.0 million upfront payment made to Acorda Therapeutics, Inc. pursuant to our June 30, 2009 collaboration and license agreement to develop and commercialize products containing fampridine in markets outside the U.S.

(g)		Resolution of federal, state and foreign tax audits, including the effective settlement of several uncertain tax positions during the fourth quarter of 2009 resulted in a $34.0 million reduction to our fourth quarter 2009 income tax expense.

Summary of Significant Accounting Policies (Details) $ in Millions	12 Months Ended
	Dec. 31, 2010 USD ($)	Dec. 31, 2009
Accounts receivable in countries with deteriorated credit and economic conditions [Line Items]
Accounts receivable in countries with deteriorated credit and economic conditions	$ 245.8
Additional Summary of Significant Accounting Policies (Textuals) [Abstract]
Interest in subsidiary (less than given percentage)	1
Deferred revenue recognized	$ 125.0
Deferred revenue to be amortized	$ 108.3
Estimated useful lives of Leasehold Improvements	Lesser of the useful life or the term of the respective lease
Accounts receivable outstanding for greater than one year	$ 45.0
Receivables that are expected to be collected beyond one year	50.1
Long-term trade receivables	$ 0.0
Percentage receivables of wholesale distributor accounted in consolidated receivables	11.50%	8.10%
Compensation expense recognized over the purchase period	fair value of the look-back provision plus the 15% discount
The purchase price of common stock under the ESPP	85% of the lower of (i) the market value per share of the common stock on the participant’s entry date into an offering period or (ii) the market value per share of the common stock on the purchase date
Buildings [Member]
Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Useful Life, Minimum	15
Property, Plant and Equipment, Useful Life, Maximum	40
Furniture and Fixtures [Member]
Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Useful Life, Average	7
Machinery and Equipment [Member]
Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Useful Life, Minimum	6
Property, Plant and Equipment, Useful Life, Maximum	15
Computer Equipment [Member]
Summary of Significant Accounting Policies (Textuals) [Abstract]
Property, Plant and Equipment, Useful Life, Minimum	3
Property, Plant and Equipment, Useful Life, Maximum	5
Greece [Member]
Accounts receivable in countries with deteriorated credit and economic conditions [Line Items]
Accounts receivable in countries with deteriorated credit and economic conditions	$ 3.9
Italy [Member]
Accounts receivable in countries with deteriorated credit and economic conditions [Line Items]
Accounts receivable in countries with deteriorated credit and economic conditions	118.0
Spain [Member]
Accounts receivable in countries with deteriorated credit and economic conditions [Line Items]
Accounts receivable in countries with deteriorated credit and economic conditions	100.6
Portugal [Member]
Accounts receivable in countries with deteriorated credit and economic conditions [Line Items]
Accounts receivable in countries with deteriorated credit and economic conditions	$ 23.3

Acquisitions (Details) - USD ($) $ in Millions	Dec. 31, 2010	Dec. 17, 2010
Purchase Price Allocation for the Acquisition [Abstract]
Cash portion of consideration		$ 32.5
Contingent consideration	$ 81.2
Panima Pharmaceuticals AG [Member]
Purchase Price Allocation for the Acquisition [Abstract]
Cash portion of consideration		32.5
Contingent consideration	81.2	81.2
Total purchase price		113.7
In process research and development	110.9
Goodwill	25.6	25.6
Deferred tax liabilities	$ 23.7	(23.7)
Other, net		(0.9)
In Process Research and Development [Member] \| Panima Pharmaceuticals AG [Member]
Purchase Price Allocation for the Acquisition [Abstract]
In process research and development		$ 110.9

Acquisitions (Details 1) - USD ($) $ in Millions	12 Months Ended
Acquisitions (Details 1) - USD ($) $ in Millions	Dec. 31, 2010	Dec. 17, 2010
Acquisitions And Dispositions (Textuals) [Abstract]
Purchase price of acquisition		$ 32.5
Maximum contingent cash payments		$ 395.0
Risk adjusted discount rate of cash flow		17.50%
Panima Pharmaceuticals AG [Member]
Acquisitions And Dispositions (Textuals) [Abstract]
Stock acquired in acquisition		100.00%
Purchase price of acquisition		$ 32.5
Discount rate used to value projects		6.10%
Research Development Commercialization Antibodies Program One [Member]
Acquisitions And Dispositions (Textuals) [Abstract]
Completion period of research, development and commercialization of three antibodies designed to treat certain neurological disorders under program one and two	2019
Expected future cost on completion of program one and other two		$ 391.0
Research Development Commercialization Antibodies Other Two Programs [Member]
Acquisitions And Dispositions (Textuals) [Abstract]
Completion period of research, development and commercialization of three antibodies designed to treat certain neurological disorders under program one and two	2021
Expected future cost on completion of program one and other two		$ 778.0
Biogen Idec Hemophilia [Member]
Acquisitions And Dispositions (Textuals) [Abstract]
Payment to former shareholders of Syntonix Pharmaceuticals	$ 40.0

Restructuring (Details) $ in Thousands	3 Months Ended	12 Months Ended
Restructuring (Details) $ in Thousands	Dec. 31, 2010 USD ($)	Dec. 31, 2010 USD ($)
Restructuring Plan Cost
Total restructuring charges		$ 75,153
Reserves established		75,200
Amounts paid		(6,600)
Additional depreciation and other non-cash charges		(2,200)
Restructuring reserves at December 31, 2010	$ 66,400	66,400
Additional Restructuring (Textuals) [Abstract]
Approximately restructuring cost due to reduction in workforce and closing and consolidation of certain leased and owned facilities		110,000
Restructuring (Textuals) [Abstract]
Headcount reduction due to consolidation of sites	13.00%
Restructuring reserves total	$ 66,400	66,400
Total Restructuring Expenditures		110,000
Workforce reduction [Member]
Restructuring Plan Cost
Total restructuring charges		67,200
Reserves established		67,200
Amounts paid		(6,600)
Restructuring reserves at December 31, 2010	60,600	60,600
Additional Restructuring (Textuals) [Abstract]
Approximately restructuring cost due to reduction in workforce and closing and consolidation of certain leased and owned facilities		90,000
Restructuring (Textuals) [Abstract]
Restructuring reserves total	60,600	60,600
Total Restructuring Expenditures		90,000
Facility consolidation [Member]
Restructuring Plan Cost
Total restructuring charges		8,000
Reserves established		8,000
Additional depreciation and other non-cash charges		(2,200)
Restructuring reserves at December 31, 2010	5,800	5,800
Additional Restructuring (Textuals) [Abstract]
Approximately restructuring cost due to reduction in workforce and closing and consolidation of certain leased and owned facilities		20,000
Restructuring (Textuals) [Abstract]
Restructuring reserves total	$ 5,800	5,800
Total Restructuring Expenditures		$ 20,000
San Diego Facility [Member]
Additional Restructuring (Textuals) [Abstract]
Sale - Leaseback transaction period in months		15

Revenue Reserves (Details) - USD ($) $ in Millions	12 Months Ended
Revenue Reserves (Details) - USD ($) $ in Millions	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Analysis of the amount of, and change in, product revenue reserves [Abstract]
Beginning balance	$ 103.1	$ 75.4	$ 59.9
Current provisions relating to sales in current year	381.7	282.3	232.4
Adjustments relating to prior years	(6.9)	0.8	(4.1)
Payments/returns relating to sales in current year	(253.8)	(185.8)	(159.1)
Payments/returns relating to sales in prior years	(82.1)	(69.6)	(53.7)
Ending balance	142.0	103.1	75.4
Discounts [Member]
Analysis of the amount of, and change in, product revenue reserves [Abstract]
Beginning balance	13.9	9.2	6.4
Current provisions relating to sales in current year	80.6	74.0	67.1
Adjustments relating to prior years	(2.7)
Payments/returns relating to sales in current year	(68.7)	(60.8)	(57.8)
Payments/returns relating to sales in prior years	(9.2)	(8.5)	(6.5)
Ending balance	13.9	13.9	9.2
Contractual Adjustments [Member]
Analysis of the amount of, and change in, product revenue reserves [Abstract]
Beginning balance	70.3	48.1	33.1
Current provisions relating to sales in current year	285.0	192.5	150.6
Adjustments relating to prior years	(2.4)		(1.6)
Payments/returns relating to sales in current year	(184.3)	(124.4)	(101.2)
Payments/returns relating to sales in prior years	(61.6)	(45.9)	(32.8)
Ending balance	107.0	70.3	48.1
Returns [Member]
Analysis of the amount of, and change in, product revenue reserves [Abstract]
Beginning balance	18.9	18.1	20.4
Current provisions relating to sales in current year	16.1	15.8	14.7
Adjustments relating to prior years	(1.8)	0.8	(2.5)
Payments/returns relating to sales in current year	(0.8)	(0.6)	(0.1)
Payments/returns relating to sales in prior years	(11.3)	(15.2)	(14.4)
Ending balance	$ 21.1	$ 18.9	$ 18.1

Revenue Reserves (Details 1) - USD ($) $ in Millions	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2007
Summary of total product revenue reserves included in consolidated balance sheets [Abstract]
Reduction of accounts receivable	$ 36.7	$ 43.3
Current liability	105.3	59.8
Total reserves	$ 142.0	$ 103.1	$ 75.4	$ 59.9

Revenue Reserves (Details 2)	3 Months Ended
Revenue Reserves (Details 2)	Mar. 31, 2010
Revenue Reserves (Textuals) [Abstract]
New minimum Medicaid rate after implementation of new Healthcare Reform	23.10%
Old minimum Medicaid rate before implementation of new Healthcare Reform	15.10%

Inventory (Details) - USD ($) $ in Thousands	12 Months Ended
Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Components of inventories [Abstract]
Raw materials	$ 59,000	$ 49,200
Work in process	142,200	174,000
Finished goods	87,900	70,800
Total inventory	289,066	293,950
Components of inventory [Line Items]
Total finished goods and work in process	230,100	244,800
Raw materials	59,000	49,200
Total inventory	289,066	293,950
Amounts written-down related to unmarketable inventory [Abstract]
Write-downs on unmarketable inventory	11,800	16,900	$ 29,800
AVONEX [Member]
Components of inventory [Line Items]
Total finished goods and work in process	87,000	76,800
TYSABRI [Member]
Components of inventory [Line Items]
Total finished goods and work in process	117,000	144,000
Others [Member]
Components of inventory [Line Items]
Total finished goods and work in process	$ 26,100	$ 24,000

Intangible Assets and Goodwill (Details) $ in Thousands	12 Months Ended
Intangible Assets and Goodwill (Details) $ in Thousands	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)
Intangible assets
Net	$ 1,772,826	$ 1,871,078
Goodwill [Roll Forward]
Beginning balance	1,138,621	1,138,600
Goodwill acquired during the year	25,600
Other	(17,900)
Ending balance	1,146,314	1,138,621	$ 1,138,600
Intangible Assets and Goodwill (Textuals) [Abstract]
Net Book Value Avonex Core Technology Intangible Asset	1,354,300	1,516,700
Amortization of acquired intangible assets	208,900	289,800	$ 332,700
Amortization of intangible assets for each of next five years, Minimum	170,000
Amortization of intangible assets for each of next five years, Maximum	$ 210,000
In Process Research and Development [Member]
Intangible assets
Estimated Life	up to 15 years upon commercialization
Cost	$ 110,900	0
Accumulated Amortization	0	0
Net	$ 110,900	0
Trademarks and tradenames [Member]
Intangible assets
Estimated Life	Indefinite
Cost	$ 64,000	64,000
Accumulated Amortization	0	0
Net	$ 64,000	64,000
Out-licensed patents [Member]
Intangible assets
Estimated Life (In Years)	12
Cost	$ 578,000	578,000
Accumulated Amortization	(350,200)	(306,000)
Net	$ 227,800	272,000
Core developed technology [Member]
Intangible assets
Estimated Life, Minimum (In Years)	15
Estimated Life, Maximum (In Years)	23
Cost	$ 3,005,300	3,005,300
Accumulated Amortization	(1,636,900)	(1,472,400)
Net	$ 1,368,400	1,532,900
In-licensed patents [Member]
Intangible assets
Estimated Life (In Years)	14
Cost	$ 3,000	3,000
Accumulated Amortization	(1,300)	(1,100)
Net	$ 1,700	1,900
Assembled workforce [Member]
Intangible assets
Estimated Life (In Years)	4
Cost	$ 2,100	2,100
Accumulated Amortization	(2,100)	(1,800)
Net	$ 0	300
Distribution rights [Member]
Intangible assets
Estimated Life (In Years)	2
Cost	$ 12,700	12,700
Accumulated Amortization	(12,700)	(12,700)
Net	0	0
Total intangible assets [Member]
Intangible assets
Cost	3,776,000	3,665,100
Accumulated Amortization	(2,003,200)	(1,794,000)
Net	1,772,800	$ 1,871,100
Panima Pharmaceuticals AG [Member]
Intangible assets
Business acquisition, purchase price allocation, in process research and development	110,900
Business Acquisition Purchase Price Allocations Goodwill Amount	$ 25,600

Fair Value Measurements (Details) - USD ($) $ in Millions	12 Months Ended
Fair Value Measurements (Details) - USD ($) $ in Millions	Dec. 31, 2010	Dec. 31, 2009	Mar. 04, 2008
Assets:
Cash equivalents	$ 651.8	$ 476.4
Derivative contracts	1.3	15.8
Plan assets for deferred compensation	13.0	13.6
Total	1,922.9	2,409.5
Liabilities:
Derivative contracts	12.2	11.1
Contingent consideration (Note 2)	81.2
Total	93.4	11.1
Fair value of venture capital investments
Beginning balance	21.9	23.9
Total net unrealized gains (losses) included in earnings	(2.1)	(3.6)
Net Purchases, issuances, and settlements	1.0	1.6
Ending balance	20.8	21.9
Summary of fair and carrying value of debt instruments
Total fair value	$ 1,135.8	1,113.3
Fair Value Measurements (Textuals) [Abstract]
Venture capital investments used in Level 3 inputs to determine the fair value of assets	approximately 0.3% of total assets
6.0% Senior notes due 2013 [Member]
Summary of fair and carrying value of debt instruments
Interest on Senior notes	6.00%
6.875% Senior notes due 2018 [Member]
Summary of fair and carrying value of debt instruments
Interest on Senior notes	6.875%		6.875%
Corporate Debt Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	$ 313.0	504.1
US Treasury and Government [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	785.3	1,133.5
Asset-backed Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	92.9	238.3
Strategic investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	44.8	5.9
Venture capital investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	20.8	21.9
Fair Value [Member] \| Dompe [Member]
Summary of fair and carrying value of debt instruments
Credit line from Dompe, Fair Value	8.1	17.2
Fair Value [Member] \| Notes Payable To Fumedica [Member]
Summary of fair and carrying value of debt instruments
Notes Payable, Fair Value	24.2	31.3
Fair Value [Member] \| 6.0% Senior notes due 2013 [Member]
Summary of fair and carrying value of debt instruments
Notes Payable, Fair Value	485.5	475.7
Fair Value [Member] \| 6.875% Senior notes due 2018 [Member]
Summary of fair and carrying value of debt instruments
Notes Payable, Fair Value	618.0	589.1
Quoted Prices in Active Markets, Level 1 [Member]
Assets:
Cash equivalents	0.0	0.0
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	44.8	5.9
Liabilities:
Derivative contracts	0.0	0.0
Contingent consideration (Note 2)	0.0
Total	0.0	0.0
Quoted Prices in Active Markets, Level 1 [Member] \| Corporate Debt Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Quoted Prices in Active Markets, Level 1 [Member] \| US Treasury and Government [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Quoted Prices in Active Markets, Level 1 [Member] \| Asset-backed Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Quoted Prices in Active Markets, Level 1 [Member] \| Strategic investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	44.8	5.9
Quoted Prices in Active Markets, Level 1 [Member] \| Venture capital investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Fair Value, Inputs, Level 2 [Member]
Assets:
Cash equivalents	651.8	476.4
Derivative contracts	1.3	15.8
Plan assets for deferred compensation	13.0	13.6
Total	1,857.3	2,381.7
Liabilities:
Derivative contracts	12.2	11.1
Contingent consideration (Note 2)	0.0
Total	12.2	11.1
Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	313.0	504.1
Fair Value, Inputs, Level 2 [Member] \| US Treasury and Government [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	785.3	1,133.5
Fair Value, Inputs, Level 2 [Member] \| Asset-backed Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	92.9	238.3
Fair Value, Inputs, Level 2 [Member] \| Strategic investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Fair Value, Inputs, Level 2 [Member] \| Venture capital investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Fair Value, Inputs, Level 3 [Member]
Assets:
Cash equivalents	0.0	0.0
Derivative contracts	0.0	0.0
Plan assets for deferred compensation	0.0	0.0
Total	20.8	21.9
Liabilities:
Derivative contracts	0.0	0.0
Contingent consideration (Note 2)	81.2
Total	81.2	0.0
Fair Value, Inputs, Level 3 [Member] \| Corporate Debt Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Fair Value, Inputs, Level 3 [Member] \| US Treasury and Government [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Fair Value, Inputs, Level 3 [Member] \| Asset-backed Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Fair Value, Inputs, Level 3 [Member] \| Strategic investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0	0.0
Fair Value, Inputs, Level 3 [Member] \| Venture capital investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	$ 20.8	$ 21.9

Financial Instruments (Details) $ in Thousands	12 Months Ended
Financial Instruments (Details) $ in Thousands	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)
Marketable Securities including Strategic Investments
Fair Value	$ 1,191,200	$ 1,875,900
Gross Unrealized Gains	3,500	16,700
Gross Unrealized Losses	(1,300)	(1,300)
Amortized Cost	1,189,000	1,860,500
Summary of Contractual Maturities: Available-for-Sale Securities
Due in one year or less, Estimated Fair Value	448,100	522,000
Due in one year or less, Amortized Cost	447,800	519,500
Due after one year through five years, Estimated Fair Value	664,100	1,143,700
Due after one year through five years, Amortized Cost	662,400	1,133,400
Due after five years, Estimated Fair Value	79,000	210,200
Due after five years, Amortized Cost	78,800	207,600
Total available-for-sale securities, Fair Value	1,191,200	1,875,900
Total available-for-sale securities, Amortized Cost	1,189,000	1,860,500
Proceeds from Marketable Securities, excluding Strategic Investments
Proceeds from maturities and sales	2,668,694	3,319,007	$ 2,941,060
Realized gains	18,800	19,800	15,900
Realized losses	$ 2,500	4,000	$ 17,000
Financial Instruments (Textuals) [Abstract]
Original maturities of commercial paper and short-term debt securities	less than 90 days
Federal Deposit Insurance Corporation guaranteed senior notes issued under the Temporary Liquidity Guarantee Program	$ 163,500	298,800
Fair and carrying values of commercial paper including accrued interest	30,000	76,900
Fair and carrying values of short-term debt securities	$ 621,800	$ 399,500
Average maturity of marketable securities, months	11	15
Number of strategic investments sold	1	2	0
Sales value of strategic investments	$ 1,800	$ 5,900
Gain (loss) from sale of strategic investments		3,000
Other-than-temporary impairment of publicly-held strategic investments	16,600	3,800	$ 16,300
Other-than-temporary impairment of privately-held companies investments	4,100	3,200	2,300
Other-than-temporary impairment of available-for-sale securities primarily related to marketable debt securities		3,600	$ 41,700
Corporate debt securities Current [Member]
Marketable Securities including Strategic Investments
Fair Value	93,200	177,200
Gross Unrealized Gains	100	1,500
Amortized Cost	93,100	175,700
Corporate debt securities Non-current [Member]
Marketable Securities including Strategic Investments
Fair Value	219,800	326,900
Gross Unrealized Gains	2,100	5,700
Gross Unrealized Losses	(500)	(300)
Amortized Cost	218,200	321,500
Government securities Current [Member]
Marketable Securities including Strategic Investments
Fair Value	352,800	501,600
Gross Unrealized Gains	200	1,200
Amortized Cost	352,600	500,400
Government securities Non-current [Member]
Marketable Securities including Strategic Investments
Fair Value	432,500	631,900
Gross Unrealized Gains	600	4,100
Gross Unrealized Losses	(600)	(500)
Amortized Cost	432,500	628,300
Mortgage and other asset backed securities Current [Member]
Marketable Securities including Strategic Investments
Fair Value	2,100	3,000
Gross Unrealized Gains		100
Amortized Cost	2,100	2,900
Mortgage and other asset backed securities Non-current [Member]
Marketable Securities including Strategic Investments
Fair Value	90,800	235,300
Gross Unrealized Gains	500	4,100
Gross Unrealized Losses	(200)	(500)
Amortized Cost	90,500	231,700
Other strategic investments Non-current [Member]
Marketable Securities including Strategic Investments
Gross Unrealized Gains	17,500	2,700
Gross Unrealized Losses		(300)
Amortized Cost	27,300	3,500
Strategic investments, non-current Fair Value	44,800	5,900
Strategic investments [Member]
Marketable Securities including Strategic Investments
Cost basis of investments in equity securities of certain privately-owned companies and venture capital funds	$ 35,000	$ 73,900

Derivative Instruments (Details) - USD ($) $ in Millions	12 Months Ended
Derivative Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Mar. 04, 2008
Foreign currency forward contracts that were entered into to hedge forecasted revenue
Total foreign currency forward contracts	$ 494.2	$ 518.2
Derivative Instruments (Textuals) [Abstract]
Lower Range of Durations of foreign currency forward contracts	1	1
Higher Range of Durations of foreign currency forward contracts	12	12
Gain/Loss on fair value of Foreign currency forward contracts	$ 11.0	$ 1.2
Expected Settlement time for contracts, in months	12
Gains and losses in earnings of Foreign currency forward contracts due to hedge ineffectiveness	$ 0.4	(1.1)	$ (0.2)
Gains/(Losses) in product revenue for the settlement of certain effective cash flow hedge instruments	45.7	(49.7)	(8.5)
Aggregate notional amount of outstanding foreign currency contracts	160.8	188.0
Fair Value of outstanding foreign currency contracts	0.1	3.8
Net gains of other income (expense) related to foreign currency forward contracts	$ 6.0	2.5
Notional Amount of Interest Rate Derivative Instruments Not Designated as Hedging Instruments			550.0
Amount received in settlement of interest rate swaps			53.9
Gains and losses in earnings of Interest rate swaps due to hedge ineffectiveness			8.9
6.875% Senior notes due 2018 [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Interest on Senior notes	6.875%			6.875%
Increased carrying amount of the 6.875% Senior Notes	$ 62.8
Reduction of interest expense	5.7	5.4
Other Current Assets [Member]
Summary of Derivatives designated as Hedging Instruments
Derivative Asset Designated as Hedging Instrument, Fair Value	0.0	10.8
Accrued Expenses and Other Liabilities [Member]
Summary of Derivatives designated as Hedging Instruments
Derivative Liability Designated as Hedging Instrument, Fair Value	11.0	9.8
Euro Member Countries, Euro
Foreign currency forward contracts that were entered into to hedge forecasted revenue
Total foreign currency forward contracts	460.3	495.9
Canada, Dollars
Foreign currency forward contracts that were entered into to hedge forecasted revenue
Total foreign currency forward contracts	24.0	22.3
Swedish krona [Member]
Foreign currency forward contracts that were entered into to hedge forecasted revenue
Total foreign currency forward contracts	9.9	0.0
Foreign Exchange Contract [Member] \| Revenue [Member]
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Amount Recognized in Accumulated Other Comprehensive Income on Derivative Gain/(Loss) (Effective Portion )	(11.0)	1.2	(44.1)
Amount Reclassified from Accumulated Other Comprehensive Income into Income Gain/(Loss) (Effective Portion )	45.7	(49.7)	(8.5)
Foreign Exchange Contract [Member] \| Other income (expense) [Member]
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Amount of Gain/(Loss) Recorded (Ineffective Portion )	$ 0.4	$ (1.1)	0.2
Interest rate swaps [Member] \| Interest Expense [Member]
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Amount of Gain/(Loss) Recorded (Ineffective Portion )			$ (8.9)

Property, Plant and Equipment (Details) $ in Thousands	1 Months Ended	12 Months Ended
Property, Plant and Equipment (Details) $ in Thousands	Oct. 31, 2010 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)
Components of property, plant and equipment, net
Land		$ 107,600	$ 111,200
Buildings		670,200	669,700
Leasehold improvements		100,800	73,100
Machinery and equipment		576,000	534,000
Computer software and hardware		392,800	334,200
Furniture and fixtures		54,500	50,700
Construction in progress		506,900	506,700
Total cost		2,408,800	2,279,600
Less: accumulated depreciation		(767,200)	(642,500)
Total property, plant and equipment, net		1,641,634	1,637,083
Net carrying amounts of the major classes of assets
Total property, plant and equipment, net		1,641,634	1,637,083
Property, Plant and Equipment (Textuals) [Abstract]
Depreciation expense		144,900	137,900	$ 129,100
Construction in progress balance related to biologic manufacturing facility		506,900	506,700
Biologic manufacturing facility [Member]
Components of property, plant and equipment, net
Construction in progress		440,200	441,200
Property, Plant and Equipment (Textuals) [Abstract]
Interest costs capitalization related to large-scale biologic manufacturing facility		28,400	28,400	$ 23,200
Construction in progress balance related to biologic manufacturing facility		440,200	$ 441,200
San Diego Facility [Member]
Components of property, plant and equipment, net
Total property, plant and equipment, net		126,400
Net carrying amounts of the major classes of assets
Total property, plant and equipment, net		$ 126,400
Property, Plant and Equipment (Textuals) [Abstract]
Acres of Land		43
Square feet of Laboratory and Office Space		355,000
Sales agreement of San Diego facility	$ 127,000	$ 127,000
Square footage to be leased, if exercise option to lease build to suit property		160,000
Lease term associated with option to lease build to suit property		10
Sale - Leaseback transaction period in months		15
Total Debt service and interest payments, Sale Leaseback Transaction		$ 6,900
Land [Member] \| San Diego Facility [Member]
Components of property, plant and equipment, net
Total property, plant and equipment, net		45,700
Net carrying amounts of the major classes of assets
Total property, plant and equipment, net		45,700
Buildings [Member] \| San Diego Facility [Member]
Components of property, plant and equipment, net
Total property, plant and equipment, net		73,000
Net carrying amounts of the major classes of assets
Total property, plant and equipment, net		73,000
Furniture and Fixtures [Member] \| San Diego Facility [Member]
Components of property, plant and equipment, net
Total property, plant and equipment, net		2,100
Net carrying amounts of the major classes of assets
Total property, plant and equipment, net		2,100
Machinery and Equipment [Member] \| San Diego Facility [Member]
Components of property, plant and equipment, net
Total property, plant and equipment, net		5,600
Net carrying amounts of the major classes of assets
Total property, plant and equipment, net		$ 5,600

Indebtedness (Details) $ in Thousands, SFr in Millions	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2006 CHF (SFr)
Current portion:
Current portion of notes payable, line of credit and other financing arrangements	$ 137,153	$ 19,762
Non-current portion:
Non-current portion of notes payable and line of credit	1,066,379	1,080,207
Total debt maturities
2011	11,400
2012	3,400
2013	453,400
2014	3,400
2015	3,400
2016 and thereafter	560,200
Total	1,035,200
Note payable to Fumedica [Member]
Current portion:
Current portion of notes payable, line of credit and other financing arrangements	3,300	11,200
Non-current portion:
Non-current portion of notes payable and line of credit \| SFr			SFr 61.4
Credit line from Domp [Member]
Current portion:
Current portion of notes payable, line of credit and other financing arrangements	8,000	8,600
6.0% Senior notes due 2013 [Member]
Non-current portion:
Non-current portion of notes payable and line of credit	449,800	449,600
6.875% Senior notes due 2018 [Member]
Non-current portion:
Non-current portion of notes payable and line of credit	597,900	603,200
San Diego Facility [Member]
Current portion:
Current portion of notes payable, line of credit and other financing arrangements	125,900	0
Dompe [Member]
Non-current portion:
Non-current portion of notes payable and line of credit	0	8,600
Notes Payable To Fumedica [Member]
Non-current portion:
Non-current portion of notes payable and line of credit	$ 18,700	$ 18,800

Indebtedness (Details 1) $ in Thousands, € in Millions, SFr in Millions	1 Months Ended		12 Months Ended
	Jun. 30, 2010 CHF (SFr)	Jun. 30, 2010 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2010 CHF (SFr)	Dec. 31, 2010 EUR (€)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 EUR (€)	Dec. 31, 2009 USD ($)	Mar. 04, 2008 USD ($)	Dec. 31, 2006 CHF (SFr)
Indebtedness (Textuals) [Abstract]
Interest to be amortized on debt						$ 51,400
Issued notes payable						1,066,379		$ 1,080,207
Notes redemption condition			At 100% of the principal amount plus accrued interest and a specified make-whole amount
Debt issuance costs						8,000
Senior unsecured revolving credit facility						360,000
San Diego Facility [Member]
Indebtedness (Textuals) [Abstract]
Remaining obligation of financing arrangements						127,000
Sale - Leaseback transaction period in months			15
Total Debt service and interest payments, Sale Leaseback Transaction						6,900
Corporate Joint Venture [Member]
Indebtedness (Textuals) [Abstract]
Loan balance of Joint Venture					€ 6.0	$ 8,000	€ 12.0	$ 17,200
Percentage of interest rate on line of credit under new agreement				2.40%	2.40%	2.40%	2.20%	2.20%
Interest rate on line of credit under new agreement is determined				three month Euro LIBOR plus 150 basis points	three month Euro LIBOR plus 150 basis points	three month Euro LIBOR plus 150 basis points
Note payable to Fumedica [Member]
Indebtedness (Textuals) [Abstract]
Issued notes payable \| SFr										SFr 61.4
Repayment of notes payable	SFr 12.0	$ 10,300
Present value of notes payable				SFr 20.7		$ 22,000
6.0% Senior notes due 2013 [Member]
Indebtedness (Textuals) [Abstract]
Principal amount of senior notes									$ 450,000
Redemption percentage of par value of Senior Notes									99.886%
Interest on Senior notes									6.00%
Issued notes payable						449,800		$ 449,600
6.875% Senior notes due 2018 [Member]
Indebtedness (Textuals) [Abstract]
Principal amount of senior notes									$ 550,000
Redemption percentage of par value of Senior Notes									99.184%
Interest on Senior notes									6.875%
Increased carrying amount of interest rate swap			$ 62,800
Issued notes payable						597,900		603,200
Dompe [Member]
Indebtedness (Textuals) [Abstract]
Issued notes payable						0		8,600
Notes Payable To Fumedica [Member]
Indebtedness (Textuals) [Abstract]
Issued notes payable						$ 18,700		$ 18,800

Equity (Details) - shares	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Summary of Preferred Stock
Preferred stock, shares authorized	8,000,000	8,000,000	8,000,000
Preferred stock, shares issued	8,000	8,000	8,000
Preferred stock, shares outstanding	8,000	8,000	8,000
Summary of common Stock
Common stock, shares authorized	1,000,000	1,000,000
Common stock, shares issued	248,200	288,494
Common stock, shares outstanding	240,538	274,855
Undesignated [Member]
Summary of Preferred Stock
Preferred stock, shares authorized	5,250,000	5,250,000	5,250,000
Preferred stock, shares issued	0	0	0
Preferred stock, shares outstanding	0	0	0
Series A [Member]
Summary of Preferred Stock
Preferred stock, shares authorized	1,750,000	1,750,000	1,750,000
Preferred stock, shares issued	8,221	8,221	8,221
Preferred stock, shares outstanding	8,221	8,221	8,221
Series X Junior Participating [Member]
Summary of Preferred Stock
Preferred stock, shares authorized	1,000,000	1,000,000	1,000,000
Preferred stock, shares issued	0	0	0
Preferred stock, shares outstanding	0	0	0

Equity (Details 1)	12 Months Ended
Equity (Details 1)	Dec. 31, 2010 USD ($) shares	Dec. 31, 2009 USD ($) shares	Dec. 31, 2008 USD ($)	Dec. 31, 2010 shares	Dec. 31, 2010 USD ($)	Dec. 31, 2009 shares	Dec. 31, 2009 USD ($)	Dec. 31, 2008 shares	Dec. 31, 2008 USD ($)
Equity (Textuals) [Abstract]
Repurchase of common stock \| $	$ 2,077,579,000	$ 751,170,000	$ 738,938,000
Preferred stock, shares authorized				8,000,000		8,000,000		8,000,000
Preferred stock, series A, shares issued				8,000		8,000		8,000
Preferred stock, series A, shares outstanding				8,000		8,000		8,000
Common shares to be issued on conversion of per preferred stock				shares 60		shares 60		shares 60
Series A [Member]
Equity (Textuals) [Abstract]
Preferred stock, shares authorized				1,750,000		1,750,000		1,750,000
Preferred stock, series A, shares issued				8,221		8,221		8,221
Preferred stock, series A, shares outstanding				8,221		8,221		8,221
Preferred Stock, liquidation preference per share \| $					$ 67		$ 67		$ 67
Series X Junior Participating [Member]
Equity (Textuals) [Abstract]
Preferred stock, shares authorized				1,000,000		1,000,000		1,000,000
Preferred stock, series A, shares issued				0		0		0
Preferred stock, series A, shares outstanding				0		0		0
Common Stock
Equity (Textuals) [Abstract]
Repurchase of common stock, shares	40,294,000	8,759,000

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2010	Dec. 31, 2009
Accumulated Other Comprehensive Income (Loss)
Translation adjustments	$ (24,400)	$ 35,600
Unrealized gains (losses) on securities available for sale	12,400	11,300
Unrealized gains (losses) on foreign currency forward contracts	(9,800)	1,500
Unfunded status of pension and postretirement benefit plans	200	2,100
Accumulated other comprehensive income (loss)	(21,610)	50,496
Accumulated Other Comprehensive Income (Loss) (Textuals) [Abstract]
Accumulated translation adjustments include in non controlling interest	(24,400)	35,600
Tax on unrealized holding gains (losses) on investments	7,300	6,600
Tax on unrealized gains (losses) on foreign currency forward contracts	1,300	300
Noncontrolling Interests
Accumulated Other Comprehensive Income (Loss)
Translation adjustments	200	2,400
Accumulated Other Comprehensive Income (Loss) (Textuals) [Abstract]
Accumulated translation adjustments include in non controlling interest	$ 200	$ 2,400

Earnings per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Numerator:
Net income (loss) attributable to Biogen Idec Inc.	$ 240,300	$ 254,100	$ 293,400	$ 217,400	$ 305,600	$ 277,700	$ 142,800	$ 244,000	$ 1,005,273	$ 970,132	$ 783,167
Adjustment for net income allocable to preferred stock									(2,000)	(1,700)	(1,300)
Net income used in calculating basic and diluted earnings per share									$ 1,003,300	$ 968,400	$ 781,900
Denominator:
Weighted average number of common shares outstanding									252,307	287,356	292,332
Effect of dilutive securities:
Stock options and employee stock purchase plan									900	600	1,300
Restricted stock awards											100
Time-vested restricted stock units									1,600	1,400	1,300
Market stock units									100
Performance-vested restricted stock units settled in shares										100
Dilutive potential common shares									2,600	2,100	2,700
Shares used in calculating diluted earnings per share									254,867	289,476	294,984
Numerator:
Net income allocable to preferred shares									$ 2,000	$ 1,700	$ 1,300
Denominator:
Stock options									4,600	8,500	6,900
Time-vested restricted stock units									100	2,100	1,500
Market stock units									0
Performance-vested restricted stock units settled in shares										200
Convertible preferred stock									500	500	500
Total									5,200	11,300	8,900
Earning Per Share (Textuals) [Abstract]
Repurchase of common stock									40,300	16,000

Share-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
Share-Based Compensation (Details) - USD ($) $ in Thousands	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	$ 171,435	$ 167,207	$ 153,748
Capitalized share-based payment costs	(3,500)	(6,300)	(7,500)
Income tax effect	(60,300)	(49,400)	(45,400)
Research and development [Member]
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	62,700	60,800	59,900
Selling, general and administrative [Member]
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	123,600	106,400	93,800
Restructuring Charges [Member]
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	6,800
Biogen Idec Inc. Shareholders' Equity
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	129,300	111,500	100,800
Total cost and expense [Member]
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	189,600	160,900	146,200
Subtotal [Member]
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	$ 193,100	$ 167,200	$ 153,700

Share-Based Compensation (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Summary of share based compensation expense associated with different programs
Stock options	$ 26,100	$ 21,600	$ 20,000
Market Stock Units	10,000
Time-vested restricted stock units	129,400	133,700	125,600
Performance-vested restricted stock units settled in shares	5,300	4,600	1,100
Performance-vested restricted stock units settled in cash	15,000
Restricted stock awards			500
Employee stock purchase plan	7,300	7,300	6,500
Capitalized share-based payment costs	(3,500)	(6,300)	(7,500)
Share-based compensation expense included in total costs and expenses	171,435	167,207	153,748
Total cost and expense [Member]
Summary of share based compensation expense associated with different programs
Share-based compensation expense included in total costs and expenses	189,600	160,900	146,200
Subtotal [Member]
Summary of share based compensation expense associated with different programs
Share-based compensation expense included in total costs and expenses	$ 193,100	$ 167,200	$ 153,700

Share-Based Compensation (Details 2) - $ / shares	12 Months Ended
Share-Based Compensation (Details 2) - $ / shares	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Weighted-average assumptions to estimate the fair value of the stock option grants awarded
Excepted option life (in years)	4.5	4.7	5.1
Excepted stock price volatility	30.80%	39.30%	34.40%
Risk-free interest rate	2.00%	1.90%	2.40%
Expected dividend yield	0.00%	0.00%	0.00%
Per share grant-date fair value	$ 16.52	$ 18	$ 20.85

Share-Based Compensation (Details 3) - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Stock option activity
Beginning Balance, Outstanding shares	10,830	12,100	14,900
Beginning Balance, Weighted Average Exercise Price	$ 52.88	$ 53.53	$ 50.03
Shares, Granted	124	1,031	1,475
Weighted Average Exercise Price, Granted	57.38	49.96	60.23
Shares, Exercised	(3,455)	(637)	(3,769)
Weighted Average Exercise Price, Exercised	$ 46.86	$ 40.16	$ 41.99
Shares, Cancelled	(332)	(1,664)	(506)
Weighted Average Exercise Price, Cancelled	$ 61.96	$ 60.74	$ 55.7
Ending Balance, Outstanding shares	7,167	10,830	12,100
Ending Balance, Weighted Average Exercise Price	$ 55.43	$ 52.88	$ 53.53

Share-Based Compensation (Details 4) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Tax benefit and cash received from stock option
Tax benefit realized for stock options	$ 16.0	$ 1.5	$ 28.0
Cash received from the exercise of stock options	$ 160.0	$ 25.2	$ 158.3

Share-Based Compensation (Details 5) - USD ($)	12 Months Ended
Share-Based Compensation (Details 5) - USD ($)	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Assumptions used in Valuation of Market Based Stock Units
Range of expected stock price volatility	30.80%	39.30%	34.40%
Market stock units [Member]
Assumptions used in Valuation of Market Based Stock Units
Expected dividend yield	0.00%
Minimum range of risk-free rates of return	0.30%
Maximum range of risk-free rates of return	2.00%
60 calendar day average stock price on grant date, minimum	$ 49.08
60 calendar day average stock price on grant date, maximum	$ 54.12
Market stock units [Member] \| Lower Range [Member]
Assumptions used in Valuation of Market Based Stock Units
Range of expected stock price volatility	38.80%
Market stock units [Member] \| Higher Range [Member]
Assumptions used in Valuation of Market Based Stock Units
Range of expected stock price volatility	28.30%

Share Based Compensation (Details 6) - Time vested Restricted stock units [Member] - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Time vested restricted stock units activity
Beginning Balance, Unvested, Shares	5,385	5,577	4,592
Beginning Balance, Weighted Average Grant Date Fair Value	$ 52.72	$ 54.26	$ 49.12
Shares, Granted	2,067	2,674	3,129
Weighted Average Grant Date Fair Value, Granted	$ 54.79	$ 48.93	$ 58.42
Shares, Vested	(2,829)	(2,421)	(1,645)
Weighted Average Grant Date Fair Value, Vested	$ 53.39	$ 52.08	$ 47.93
Shares, Forfeited	(400)	(445)	(499)
Weighted Average Grant Date Fair Value, Forfeited	$ 52.93	$ 53.02	$ 53.95
Ending Balance, Unvested, Shares	4,223	5,385	5,577
Ending Balance, Weighted Average Grant Date Fair Value	$ 53.26	$ 52.72	$ 54.26

Share Based Compensation (Details 7) - Performance vested Restricted stock units [Member] - USD ($) shares in Thousands	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Performance-vested restricted stock units (PVRSUs) activity
Beginning Balance, Unvested, Shares	288	90	120
Beginning Balance, Weighted Average Grant Date Fair Value	$ 49.39	$ 52.29	$ 51.55
Shares, Granted	4	325
Weighted Average Grant Date Fair Value, Granted	$ 53.64	$ 49.42
Shares, Vested	(129)	(30)	(27)
Weighted Average Grant Date Fair Value, Vested	$ 49.69	$ 52.29	$ 49.33
Shares, Forfeited	(9)	(97)	(3)
Weighted Average Grant Date Fair Value, Forfeited	$ 49.56	$ 51.3	$ 49.33
Ending Balance, Unvested, Shares	154	288	90
Ending Balance, Weighted Average Grant Date Fair Value	$ 49.24	$ 49.39	$ 52.29

Share-Based Compensation (Details 8) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Shares issued under employee stock purchase plan
Shares issued under ESPP	0.6	0.6	0.5
Cash received under ESPP	$ 23.5	$ 22.6	$ 21.3

Share-Based Compensation (Details 9)	3 Months Ended	5 Months Ended	6 Months Ended	12 Months Ended			18 Months Ended
Share-Based Compensation (Details 9)	Dec. 31, 2010 USD ($) shares	Jun. 08, 2010 USD ($)	Dec. 31, 2010 USD ($) shares	Dec. 31, 2010 USD ($) shares	Dec. 31, 2009 USD ($) shares	Dec. 31, 2008 USD ($) shares	Dec. 31, 2011
Share Based Payments (Textuals) [Abstract]
Windfall tax benefits from vesting of stock awards, exercises of stock options and ESPP participation				$ 13,100,000	$ 3,400,000	$ 28,000,000
Unrecognized compensation cost related to unvested share-based compensation	$ 130,500,000		$ 130,500,000	$ 130,500,000
Weighted-average period to recognize the cost of unvested awards	1.3		1.3	1.3
Number of share-based compensation plans pursuant to which awards are currently being made				3
Number of share-based compensation plans pursuant to which no further awards will be made				6
Term of stock option grants to employees				10
Term of stock option grants to directors				10
Term of stock option vest to employees (in years)				4
Outstanding stock options exercisable \| shares	6,000,000		6,000,000	6,000,000
Weighted-average exercise price	$ 55.68		$ 55.68	$ 55.68
Aggregate intrinsic value of options exercisable	$ 69,400,000		$ 69,400,000	$ 69,400,000
Weighted average remaining contractual term for options exercisable	3.6		3.6	3.6
Total of vested and expected to vest options outstanding \| shares	6,900,000		6,900,000	6,900,000
Weighted average exercise price for vested and expected to vest options	$ 55.48		$ 55.48	$ 55.48
Aggregate intrinsic value of vested and expected to vest options	$ 81,300,000		$ 81,300,000	$ 81,300,000
Weighted average remaining contractual term of vested and expected to vest options	4.2		4.2	4.2
Total intrinsic value of options exercised				$ 50,500,000	$ 6,700,000	$ 85,100,000
Aggregate intrinsic values of options outstanding	$ 84,900,000		$ 84,900,000	$ 84,900,000
Weighted average remaining contractual term for options outstanding	4.3		4.3	4.3
Term of grant vested to board of director				3
Restructuring charge				$ 75,153,000
Total Restructuring Expenditures				$ 110,000,000
Number of equal annual increments for cash Settled Performance Shares awards				3
Grant vested to employees				one-third per year over three years
Incremental charge related to stock options, RSUs and PVRSUs		$ 18,600,000
Workforce reduction [Member]
Share Based Payments (Textuals) [Abstract]
Restructuring charge				$ 67,200,000
Total Restructuring Expenditures				$ 90,000,000
Restricted Stock Awards [Member]
Share Based Payments (Textuals) [Abstract]
Term of stock option vest to employees (in years)				3
Grant vested to employees				one-third per year over three years
Market stock units [Member]
Share Based Payments (Textuals) [Abstract]
Number of shares granted \| shares				405,000
Weighted average grant date fair value				$ 61.87
Percentage of earnings of the target number of units granted based on actual stock performance (Minimum)				0.00%
Percentage of earnings of the target number of units granted based on actual stock performance (Maximum)				150.00%
Number of annual increments for MSU awards				4
Time vested Restricted stock units [Member]
Share Based Payments (Textuals) [Abstract]
Term of stock option grants to employees				3
Grant vested to employees per year				one-third per year over three years
Number of shares granted \| shares				2,067,000	2,674,000	3,129,000
Weighted average grant date fair value				$ 54.79	$ 48.93	$ 58.42
Number of shares vested, reflecting the fact that certain shares were withheld for income tax purposes \| shares				2,829,000	2,421,000	1,645,000
Performance vested Restricted stock units [Member]
Share Based Payments (Textuals) [Abstract]
Number of shares granted \| shares				4,000	325,000
Weighted average grant date fair value				$ 53.64	$ 49.42
Maximum percentage of earnings of the target number of shares granted if maximum threshhold limit is attained					200.00%
Number of shares vested, reflecting the fact that certain shares were withheld for income tax purposes \| shares				(129,000)	(30,000)	(27,000)
Cash settled performance shares [Member]
Share Based Payments (Textuals) [Abstract]
Number of shares granted \| shares				380,000
Percentage of earnings of the target number of units granted based on actual stock performance (Minimum)				0.00%
Percentage of earnings of the target number of units granted based on actual stock performance (Maximum)				200.00%
Number of days for calculation of average closing stock price				60
Employee Stock Option [Member]
Share Based Payments (Textuals) [Abstract]
Grant vested to employees				one-fourth per year over four years
Directors Plan [Member]
Share Based Payments (Textuals) [Abstract]
Total number of shares of common stock for issuance \| shares				1,600,000
Ratio of total number of shares reserved under the plan				1.5-to-1
Omnibus Plans [Member]
Share Based Payments (Textuals) [Abstract]
Total number of shares of common stock for issuance \| shares				15,000,000
Ratio of total number of shares reserved under the plan				1.5-to-1
Chief Executive Officer [Member]
Share Based Payments (Textuals) [Abstract]
Retirement age as per terms and conditions							Awards made to Dr. Scangos are subject to the same terms and conditions as other grants except that if Dr. Scangos retires from the Company after reaching the age of 65, any outstanding and unvested RSUs and CSPSs, if granted, will continue to vest as if Dr. Scangos continued to be employed by the Company.
Chief Executive Officer [Member] \| Restricted Stock Awards [Member]
Share Based Payments (Textuals) [Abstract]
Number of shares granted \| shares			63,165
Chief Executive Officer [Member] \| Market stock units [Member]
Share Based Payments (Textuals) [Abstract]
Number of shares granted \| shares			56,905
Award Modification [Member] \| Workforce reduction [Member]
Share Based Payments (Textuals) [Abstract]
Restructuring charge	$ 6,800,000

Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
Income Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Income before income taxes (benefit):
Domestic	$ 846,400	$ 1,073,800	$ 829,200
Foreign	383,500	258,900	326,700
Total	1,229,906	1,332,679	1,155,883
Current
Federal	357,700	439,900	431,200
State	19,600	3,100	24,300
Foreign	35,400	50,000	49,800
Total	412,700	493,000	505,300
Deferred
Federal	(70,600)	(94,800)	(119,200)
State	(6,600)	(39,000)	(20,000)
Foreign	(4,200)	(3,600)	(300)
Total	(81,410)	(137,351)	(139,549)
Total income tax expense	331,333	355,617	$ 365,776
Components of deferred tax assets and liabilities
Tax credits	47,600	35,200
Inventory, other reserves and accruals	203,100	166,400
Capitalized costs	6,700	8,700
Intangibles, net	61,800	83,200
Net operating loss	35,300	30,500
Share-based compensation	64,400	60,800
Other	70,300	60,600
Valuation allowance	(10,800)	0
Total deferred tax assets	478,400	445,400
Purchased intangible assets	(446,100)	(475,400)
Unrealized gain on investments and cumulative translation adjustment	(6,600)	(6,300)
Depreciation, amortization and other	(114,400)	(115,600)
Total deferred tax liabilities	$ (567,100)	$ (597,300)
Reconciliation between the U.S. federal statutory tax rate and effective tax rate
Statutory rate	35.00%	35.00%	35.00%
State taxes	1.70%	(0.10%)	1.60%
Taxes on foreign earnings	(10.70%)	(5.00%)	(5.80%)
Credits and net operating loss utilization	(3.00%)	(3.80%)	(2.90%)
Purchased intangible assets	1.90%	2.00%	3.70%
IPR&D	5.00%		0.80%
Permanent items	(2.00%)	(1.30%)	(0.90%)
Other	(1.00%)	(0.10%)	0.10%
Effective tax rate	26.90%	26.70%	31.60%
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Beginning Balance	$ 147,100	$ 249,600	$ 221,100
Additions based on tax positions related to the current period	3,600	14,400	21,800
Additions for tax positions of prior periods	13,300	77,400	20,400
Reductions for tax positions of prior periods	(18,500)	(88,700)	(13,700)
Statute expirations	(3,700)
Settlements	(20,300)	(105,600)
Ending Balance	$ 121,500	$ 147,100	$ 249,600

Income Taxes (Details) (Textual) - USD ($) $ in Millions	12 Months Ended
Income Taxes (Details) (Textual) - USD ($) $ in Millions	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Jun. 08, 2010	Dec. 31, 2006	Sep. 30, 2006
Income Taxes (Textuals) [Abstract]
Undistributed foreign earnings of non-U.S. subsidiaries	$ 2,400.0
Unrecognized tax benefits, if recognized, would affect the effective income tax rate in future periods	26.2	$ 42.8	$ 155.1
Net interest expense (benefit)	0.7	(3.1)	$ 16.1
Accrued payment of interest	29.4	33.1
Notice of Assessment of corporate excise tax including penalties and interest	142.4			$ 103.5	$ 38.9	$ 38.9
Tax settlement payments made	13.8	118.0
Future payment for settlement of income tax	76.1
Decrease in net unrecognized tax benefits recorded as a benefit		123.5
Net unrecognized tax benefits recorded as a benefit		$ 28.0
General Business [Member] \| Domestic Country [Member]
Income Taxes (Textuals) [Abstract]
Net operating losses credit carry forwards	55.8
Credit carry forwards	$ 14.8
Tax credit carryforward, expiration dates	2020
General Business [Member] \| State and Local Jurisdiction [Member]
Income Taxes (Textuals) [Abstract]
Net operating losses credit carry forwards, State	$ 184.7
Tax credit carry forward, expiration dates	2010
Research [Member] \| State and Local Jurisdiction [Member]
Income Taxes (Textuals) [Abstract]
Credit carry forwards	$ 56.8
Tax credit carry forward, expiration dates	2011
Carrying balance of research and investment credit expire in 2011	$ 53.4

Other Consolidated Financial Statement Detail (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 17, 2010
Cash paid during the year for:
Interest									$ 68,100	$ 68,100	$ 40,000
Income taxes									394,700	745,400	372,000
Other income (expense), net
Interest income									22,300	48,500	72,100
Interest expense									(36,100)	(35,800)	(52,000)
Impairments of investments									(21,300)	(10,600)	(60,300)
Gain (Loss) on sales of investments, net									16,300	22,800	(1,100)
Foreign exchange gain (losses), net									(3,500)	11,400	(9,800)
Other, Net									3,300	1,000	(6,600)
Total other income (expense), net	$ (4,700)	$ (6,900)	$ 1,000	$ (8,400)	$ 6,400	$ 9,400	$ 14,700	$ 6,800	(18,983)	37,252	(57,728)
Other Current Assets
Deferred tax assets	112,200				88,800				112,200	88,800
Prepaid taxes	31,400				11,000				31,400	11,000
Receivable from collaborations	7,300				5,300				7,300	5,300
Interest receivable	4,900				10,600				4,900	10,600
Other prepaid expenses	47,900				41,600				47,900	41,600
Other	12,100				20,600				12,100	20,600
Other current assets	215,822				177,924				215,822	177,924
Accrued Expenses and Other
Employee compensation and benefits	159,700				127,100				159,700	127,100
Revenue-related rebates	90,100				52,000				90,100	52,000
Restructuring charges	66,400				0				66,400	0
Royalties and licensing fees	45,100				41,800				45,100	41,800
Deferred Revenue	41,300				38,700				41,300	38,700
Collaboration expenses	31,600				35,700				31,600	35,700
Clinical development expenses	24,400				43,200				24,400	43,200
Construction in progress accrual	16,400				12,800				16,400	12,800
Interest payable	21,600				21,600				21,600	21,600
Current portion of contingent consideration	11,900								11,900
Other	157,400				127,900				157,400	127,900
Total accrued expense and other	665,900				$ 500,800				665,900	$ 500,800
Business Acquisition [Line Items]
Contingent consideration liability assumed	81,200								81,200
Other Consolidated Financial Statement Detail (Textuals) [Abstract]
Sold development rights on parcel of land											11,400
(Gain) loss on sale of property, plant and equipment, net									(1,643)		$ 9,242
Panima Pharmaceuticals AG [Member]
Business Acquisition [Line Items]
In process research and development	110,900								110,900
Contingent consideration liability assumed	81,200								81,200			$ 81,200
Goodwill	25,600								25,600			25,600
Deferred tax liability assumed	$ 23,700								$ 23,700			$ (23,700)

Investments in Variable Interest Entities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Cardiokine [Member]
Summary of activity related to collaborations
Milestone payments made to collaborative partner		$ 20.0
Total development expense incurred by the collaboration excluding upfront and milestone payments	$ 51.1	66.5	$ 50.5
Biogen Idec's share of expense incurred by the collaboration reflected within our consolidated statements of income	46.0	79.8	45.5
Collaboration expense allocated to noncontrolling interests, net of tax	5.1	6.7	5.0
Summary of activity related to collaboration, along with an estimate of additional future development expense
Total upfront and milestone payments made to Collaborative Partner	70.0
Total development expense incurred by collaboration, excluding upfront and milestone payments	173.9
Neurimmune [Member]
Summary of activity related to collaborations
Milestone payments made to collaborative partner		7.5	10.5
Total development expense incurred by the collaboration excluding upfront and milestone payments	15.5	9.0	5.9
Biogen Idec's share of expense incurred by the collaboration reflected within our consolidated statements of income	15.5	$ 16.5	$ 16.4
Other payments to noncontrolling interests, net of tax	1.0
Summary of activity related to collaboration, along with an estimate of additional future development expense
Total upfront and milestone payments made to Collaborative Partner	20.0
Total development expense incurred by collaboration, excluding upfront and milestone payments	31.0
Estimate of additional amounts to be incurred by us in Product development	539.5
Knopp [Member]
Summary of activity related to collaborations
Total upfront and reimbursement payment made to collaborative partner	26.4
Total development expense incurred by the collaboration excluding upfront and milestone payments	5.0
Biogen Idec's share of expense incurred by the collaboration reflected within our consolidated statements of income	$ 31.4

Investments in Variable Interest Entities (Details 1) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Investment in Variable Interest Entities (Textuals) [Abstract]
Research and development	$ 1,248,604	$ 1,283,068	$ 1,072,058
Total joint venture assets	159,200
Total joint venture liabilities	63,300
Account receivable from ordinary course of business related to Joint Ventures	124,200
Investment in biotechnology that determined to be unconsolidated variable interest entities	22,900
Cardiokine [Member]
Investment in Variable Interest Entities (Textuals) [Abstract]
Development costs final payment under the amended collaboration	$ 25,000
Percentage of funding for R&D cost required in support of the collaboration agreement	90.00%
Total upfront and milestone payments made to Collaborative Partner	$ 70,000
Total development expense incurred by collaboration, excluding upfront and milestone payments	173,900
Termination payment	25,000
Milestone payments made to Neurimmune		20,000
Neurimmune [Member]
Investment in Variable Interest Entities (Textuals) [Abstract]
Remaining potential development milestone payments and royalties on commercial sales under the terms of collaboration agreement	$ 360,000
Percentage of funding for R&D cost required in support of the collaboration agreement	100.00%
Total upfront and milestone payments made to Collaborative Partner	$ 20,000
Total development expense incurred by collaboration, excluding upfront and milestone payments	31,000
Milestone payments made to Neurimmune		$ 7,500	$ 10,500
Knopp [Member]
Investment in Variable Interest Entities (Textuals) [Abstract]
Remaining potential development milestone payments and royalties on commercial sales under the terms of collaboration agreement	265,000
Total upfront and reimbursement payment made to collaborative partner	$ 26,400
Minimum number of years of product term from the first commercial sales	10
Purchase Of Class B Common Shares In Variable Interest Entities	30.00%
Purchase Consideration For Variable Interest Entities	60,000
Research and development	$ 205,000
Discount Rate To Value Assets	14.00%
Allocated Research And Development Charge To Noncontrolling Interest	$ 145,000

Collaborations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Collaborations (Details) - USD ($) $ in Thousands	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Mar. 31, 2008
Revenues from unconsolidated joint business
Product	$ 909,800	$ 876,900	$ 859,200	$ 824,200	$ 826,800	$ 801,700	$ 791,000	$ 733,400	$ 3,470,056	$ 3,152,941	$ 2,839,651
Unconsolidated joint business	$ 258,000	$ 258,000	$ 306,400	$ 254,900	$ 256,600	$ 283,900	$ 275,600	$ 278,800	1,077,244	1,094,863	1,128,238
Roche Group - Genentech [Member]
Revenues from unconsolidated joint business
Unconsolidated joint business									1,077,200	1,094,900	1,128,200
Roche Group - Genentech [Member] \| U. S. [Member]
Revenues from unconsolidated joint business
Biogen Idec's share of co-promotion profits in the U.S.									848,000	773,600	733,500
Reimbursement of selling and development expenses in the U.S.									58,300	65,600	59,700
RITUXAN [Member] \| U. S. [Member]
Revenues from unconsolidated joint business
Reimbursement of selling and development expenses in the U.S.									$ 58,300	65,600	59,700
RITUXAN [Member] \| After First New Product FDA Approval [Member]
Co-promotion profit sharing formula
First $ 50.0 million	30.00%								30.00%
Until First GA 101 Threshold Date	38.00%								38.00%
After First GA 101 Threshold Date
Until First Threshold Date	37.50%								37.50%
After First Threshold Date and until Second Threshold Date	35.00%								35.00%
After Second Threshold Date	30.00%								30.00%
RITUXAN [Member] \| Roche Group - Genentech [Member]
Co-promotion profit sharing formula
Above $50.0 million				40.00%				40.00%				40.00%
RITUXAN [Member] \| Roche Group - Genentech [Member] \| Outside the U. S. [Member]
Revenues from unconsolidated joint business
Product									$ 170,900	$ 255,700	$ 335,000
RITUXAN [Member] \| First Non-CLL GA 101 FDA Approval Occurs First [Member] \| Before First New Product FDA Approval [Member]
Co-promotion profit sharing formula
First $ 50.0 million	30.00%								30.00%
Until First GA 101 Threshold Date	39.00%								39.00%
After First GA 101 Threshold Date
Until Second GA 101 Threshold Date	37.50%								37.50%
After Second GA 101 Threshold Date	35.00%								35.00%
RITUXAN [Member] \| GA 101 CLL Sales Trigger Occurs First [Member] \| Before First New Product FDA Approval [Member]
Co-promotion profit sharing formula
First $ 50.0 million	30.00%								30.00%
Above $50.0 million	35.00%								35.00%

Collaborations (Details 1) - Acorda [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009
Summary of activity related to collaboration with Aroda
Upfront and milestone payments made to Acorda	$ 0.0	$ 110.0
Total expense incurred by Biogen Idec excluding upfront and milestone payments	22.8	4.7
Total expense reflected within research and development expense	22.8	$ 114.7
Summary of activity related to collaboration with Acorda, along with an estimate of additional future development expense
Total upfront and milestone payments made to Collaborative Partner	110.0
Total development expense incurred by collaboration, excluding upfront and milestone payments	27.5
Fampridine Sr [Member]
Summary of activity related to collaboration with Acorda, along with an estimate of additional future development expense
Estimate of additional amounts to be incurred by us in Product development	$ 89.0

Collaborations (Details 2) - Swedish Orphan Biovitrum [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Summary of activity related to collaboration with Swedish Orphan Biovitrum
Total expense incurred by collaboration	$ 78.9	$ 44.9	$ 33.7
Total expense reflected within research and development expense	78.5	$ 22.5	$ 18.8
Summary of activity related to collaboration with Swedish Orphan Biovitrum, along with an estimate of additional future development expense
Total upfront and milestone payments received from Collaborative Partner	5.0
Total development expense incurred by collaboration, excluding upfront and milestone payments	133.1
Factors XII And IX [Member]
Summary of activity related to collaboration with Swedish Orphan Biovitrum, along with an estimate of additional future development expense
Estimate of additional amounts to be incurred by us in Product development	$ 314.3

Collaborations (Details 3) - Abbott Biotherapeutics [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Summary of activity related to collaboration with Facet Biotech
Total expense incurred by collaboration	$ 74.8	$ 40.8	$ 65.7
Total expense reflected within research and development expense	37.4	$ 20.4	$ 32.8
Summary of activity related to collaboration with Facet Biotech, along with an estimate of additional future development expense
Total upfront and milestone payments made to Collaborative Partner	80.0
Total development expense incurred by collaboration, excluding upfront and milestone payments	159.9
Estimate of additional amounts to be incurred by us in Product development	$ 456.0

Collaborations (Details 4) - UCB [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Summary of activity related to collaboration with UCB
Total expense incurred by collaboration	$ 2.2	$ 31.8	$ 33.6
Total expense reflected within research and development expense	1.6	$ 21.0	$ 21.9
Summary of activity related to collaboration with UCB, along with an estimate of additional future development expense
Total upfront and milestone payments made to Collaborative Partner	30.0
Total development expense incurred by collaboration, excluding upfront and milestone payments	72.6
Estimate of additional amounts to be incurred by us in Product development	$ 0.0

Collaborations (Details 5) - Vernalis [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Summary of activity related to collaboration with Vernalis
Total expense incurred by collaboration and reflected within our consolidated statements of income	$ 16.2	$ 14.8	$ 16.9
Summary of activity related to collaboration with Vernalis, along with an estimate of additional future development expense
Total upfront and milestone payments made to Collaborative Partner	13.0
Total development expense incurred by collaboration, excluding upfront and milestone payments	85.9
Estimate of additional amounts to be incurred by us in Product development	$ 323.5

Collaborations (Details 6) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended			19 Months Ended
Collaborations (Details 6) - USD ($) $ in Thousands	Mar. 31, 2009	Sep. 30, 2008	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 31, 2010	Mar. 31, 2010	Mar. 31, 2008
Collaborations (Textuals) [Abstract]
Research and development			$ 1,248,604	$ 1,283,068	$ 1,072,058
Impairment charge of investment in collaboration company			21,300	10,600	60,300
Copromotion operating profit threshold for Rituxan in US and Canada to determine share of copromotion operating profit prior to amendment			$ 50,000			$ 50,000
Percentage of share of copromotion profits exceeding $50 million, prior to amendment			40.00%			40.00%
Roche Group - Genentech [Member]
Collaborations (Textuals) [Abstract]
Number of members in Joint Development Committee			3
Roche Group - Genentech [Member] \| U. S. [Member]
Collaborations (Textuals) [Abstract]
Reimbursement of selling and development expenses in the U.S.			$ 58,300	65,600	59,700
Elan [Member]
Collaborations (Textuals) [Abstract]
Milestone payments received under collaboration agreement	$ 50,000	$ 75,000
Deferred revenue for the inventory pending shipment of TYSABRI			20,800	23,600		$ 20,800
Reimbursements of research and developments expense from Elan			49,800	25,300	23,600
Reimbursements of selling, generaland administrative expenses from Elan			68,500	62,500	33,700
Amount reflected in collaboration profit sharing line for collaboration			258,100	215,900	136,000
Acorda [Member]
Collaborations (Textuals) [Abstract]
Upfront payment made and recorded as product research and development expense			0	110,000
Expected additional milestone payments for successful achievement of regulatory and commercial sales milestones			$ 400,000			400,000
Percentage of upfront and milestone payments to be made to collaboration company			7.00%
Abbott Biotherapeutics [Member]
Collaborations (Textuals) [Abstract]
Estimated additional payments upon achievement of development and commercial milestones			$ 180,000			180,000
Vernalis [Member]
Collaborations (Textuals) [Abstract]
Expected milestone payments upon achievement of certain objectives, as well as royalties on commercial sales			85,000			85,000
Fair value of investment in Vernalis, approximately			$ 200	500		$ 200
Ocrelizumab [member] \| Minimum [Member]
Collaborations (Textuals) [Abstract]
Future royalties percentage to be received on sale of ocrelizumab			13.50%
Ocrelizumab [member] \| Maximum [Member]
Collaborations (Textuals) [Abstract]
Future royalties percentage to be received on sale of ocrelizumab			24.00%
GA101 [Member]
Collaborations (Textuals) [Abstract]
Percentage of future development and commercialization expenses payable related to GA101			0.35
Sharing percentage of development expenses of GA 101, Prior to Amendment			30.00%
Compensation payment under terms of Amendment for reimbursement of increased share of previously incurred expenses			$ 10,000
GA101 [Member] \| Minimum [Member]
Collaborations (Textuals) [Abstract]
Profit sharing on sale of GA 101, percentage			35.00%
GA101 [Member] \| Maximum [Member]
Collaborations (Textuals) [Abstract]
Profit sharing on sale of GA 101, percentage			39.00%
RITUXAN [Member]
Collaborations (Textuals) [Abstract]
Royalties to be received under the Collaboration Agreement			10% to 12% royalties will be paid on sales of RITUXAN outside the U.S. and Canada for a period lasting 11 years
Royalty period for substantially all of the remaining royalty-bearing sales of RITUXAN in the rest of world			expire through 2012
Threshold of gross sales of New Product to be achieved in same calendar year under sub option one and two of option two			$ 150,000
Threshold of gross sales of new product to be achieved in any calendar year under sub option three of option two			350,000
RITUXAN [Member] \| U. S. [Member]
Collaborations (Textuals) [Abstract]
Reimbursement of selling and development expenses in the U.S.			$ 58,300	65,600	59,700
RITUXAN [Member] \| After First New Product FDA Approval [Member]
Collaborations (Textuals) [Abstract]
Percentage of Co promotion Operating Profits first fifty million			30.00%			30.00%
RITUXAN [Member] \| Roche Group - Genentech [Member]
Collaborations (Textuals) [Abstract]
Percentage of share of copromotion profits exceeding $50 million	40.00%						40.00%	40.00%
RITUXAN [Member] \| First Non-CLL GA 101 FDA Approval Occurs First [Member] \| Before First New Product FDA Approval [Member]
Collaborations (Textuals) [Abstract]
Percentage of Co promotion Operating Profits first fifty million			30.00%			30.00%
RITUXAN [Member] \| GA 101 CLL Sales Trigger Occurs First [Member] \| Before First New Product FDA Approval [Member]
Collaborations (Textuals) [Abstract]
Percentage of Co promotion Operating Profits first fifty million			30.00%			30.00%
Percentage of share of copromotion profits exceeding $50 million			35.00%			35.00%
RITUXAN [Member] \| GA101 [Member]
Collaborations (Textuals) [Abstract]
GA101 CLL Sales Trigger - US GA101 gross sales threshold			$ 500,000
Threshold of gross sales to be achieved in preceding 12 consecutive months under option one			150,000
Threshold of gross sales to be achieved in any 12 consecutive months under option one			150,000
Threshold of earlier of GA101 CLL trigger, the second GA101 CLL sales trigger, and gross sales of New Product to be achieved in any calendar year under sub option one and two of option two			$ 150,000
Oral Alpha Four Integrin Antagonist [Member] \| UCB [Member]
Collaborations (Textuals) [Abstract]
Research and development						$ 102,600
New Anti CD20 [Member] \| Roche Group - Genentech [Member] \| U. S. [Member]
Collaborations (Textuals) [Abstract]
Percentage of Co promotion Operating Profits first fifty million			30.00%			30.00%
Percentage of share of copromotion profits exceeding $50 million			40.00%			40.00%
New Anti CD20 [Member] \| Third Party Anti-CD20 [Member] \| Roche Group - Genentech [Member]
Collaborations (Textuals) [Abstract]
Research and development			$ 50,600	$ 62,500	$ 43,600
New Anti CD20 [Member] \| Until such sales exceed One Hundred And Fifty million in any calendar year [Member]
Collaborations (Textuals) [Abstract]
Percentage of share of copromotion profits exceeding $50 million			38.00%			38.00%
New Anti CD20 [Member] \| After such sales exceed One Hundred And Fifty million in any calendar year until such sales exceed Three Hundred And Fifty million in any calendar year [Member]
Collaborations (Textuals) [Abstract]
Percentage of share of copromotion profits exceeding $50 million			35.00%			35.00%
New Anti CD20 [Member] \| After such sales exceed Three Hundred And Fifty million in any calendar year [Member]
Collaborations (Textuals) [Abstract]
Percentage of share of copromotion profits exceeding $50 million			30.00%			30.00%

Litigation (Details) $ in Millions	12 Months Ended
Litigation (Details) $ in Millions	Dec. 31, 2010 USD ($)	Jun. 08, 2010 USD ($)	Dec. 31, 2006 USD ($)	Sep. 30, 2006 USD ($)
Litigation (Textuals) [Abstract]
Notice of Assessment under consideration for corporate excise tax	$ 142.4	$ 103.5	$ 38.9	$ 38.9
Estimated Royalties and interest based on a 0.5% stipulated royalty rate if awarded in connection with RITUXAN	$ 100.0
Stipulated royalty rate	0.50%
Number of consolidated lawsuits	2

Commitments and Contingencies (Details) $ in Thousands	1 Months Ended	12 Months Ended
Commitments and Contingencies (Details) $ in Thousands	Oct. 31, 2010 USD ($)	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)
Minimum rental commitments under noncancellable leases
Minimum lease payments, 2011		$ 40,900
Minimum lease payments, 2012		31,100
Minimum lease payments, 2013		32,600
Minimum lease payments, 2014		31,100
Minimum lease payments, 2015		26,500
Minimum lease payments, Thereafter		205,600
Minimum lease payments, Total		367,800
Income from subleases, 2011		(400)
Income from subleases, 2012		(400)
Income from subleases, 2013		(500)
Income from subleases, 2014		(400)
Income from subleases, 2015		0
Income from subleases, Thereafter		0
Income from subleases, Total		(1,700)
Net minimum lease payments, 2011		40,500
Net minimum lease payments, 2012		30,700
Net minimum lease payments, 2013		32,100
Net minimum lease payments, 2014		30,700
Net minimum lease payments, 2015		26,500
Net minimum lease payments, Thereafter		205,600
Net minimum lease payments, Total		366,100
Long-term Purchase Commitment [Line Items]
Remaining obligation on sale agreement of San Diego facility		137,153	$ 19,762
Commitments and Contingencies (Textuals) [Abstract]
Lease Rent Expense which terminates at various dates		44,800	36,400	$ 36,000
Approximately funding commitments in biotechnology oriented venture capital funds		19,000
Accrued expenses on funding commitment related to clinical research		16,100
Potential future milestone payments commitment to third party, approximately		1,334,300
Cancellable future commitments		326,900
San Diego Facility [Member]
Long-term Purchase Commitment [Line Items]
Total Debt service and interest payments, Sale Leaseback Transaction		6,900
Sales agreement of San Diego facility	$ 127,000	127,000
Remaining obligation on sale agreement of San Diego facility		$ 125,900	$ 0
Sale - Leaseback transaction period in months		15

Employee Benefit Plans (Details) $ in Millions	12 Months Ended
Employee Benefit Plans (Details) $ in Millions	Dec. 31, 2010 USD ($)	Dec. 31, 2009 USD ($)	Dec. 31, 2008 USD ($)
Savings plan [Member]
Employee Benefit Plans (Textuals) [Abstract]
Minimum qualifying age for Employee Benefit Plan (in years)	21
Previous matching contributions vesting period (in years)	4
Expenses related to savings plan	$ 26.3	$ 27.9	$ 22.8
Supplemental Savings Plan [Member]
Employee Benefit Plans (Textuals) [Abstract]
Deferred compensation related to Employee Benefit Plan	$ 62.2	63.6
Deferred Compensation Plan [Member]
Employee Benefit Plans (Textuals) [Abstract]
Previous restoration match vesting period	4
Previous transition contributions vesting period (in years)	7
German Plan [Member]
Employee Benefit Plans (Textuals) [Abstract]
Employee Benefit Plan obligations	$ 8.2	5.7
Periodic pension cost	$ 1.1	$ 1.1	$ 1.0

Segment Information (Details)	12 Months Ended
Segment Information (Details)	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Segment Information (Textuals) [Abstract]
Revenues from unconsolidated joint business in percentage	23.00%	25.00%	28.00%

Segment Information (Details 1) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Segment Information (Details 1) - USD ($) $ in Thousands	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues	$ 909,800	$ 876,900	$ 859,200	$ 824,200	$ 826,800	$ 801,700	$ 791,000	$ 733,400	$ 3,470,056	$ 3,152,941	$ 2,839,651
Entity Wide Information Revenue From External Customer (Numeric)
Long-lived assets related to operations in Denmark	1,838,600				1,805,400				1,838,600	1,805,400	1,777,900
UNITED STATES [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									1,744,400	1,638,000	1,472,900
Rest of World [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									1,725,700	1,514,900	1,366,800
DENMARK [Member]
Entity Wide Information Revenue From External Customer (Numeric)
Long-lived assets related to operations in Denmark	$ 644,700				$ 665,800				$ 644,700	$ 665,800	$ 611,500
Distributor One [Member]
Entity Wide Information Revenue From External Customer (Numeric)
Entity wide percentage of revenue from major distributors									18.00%	18.00%	16.00%
Distributor Two [Member]
Entity Wide Information Revenue From External Customer (Numeric)
Entity wide percentage of revenue from major distributors									11.00%	12.00%	13.00%
AVONEX [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									$ 2,518,400	$ 2,322,900	$ 2,202,600
AVONEX [Member] \| UNITED STATES [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									1,491,600	1,406,200	1,276,500
AVONEX [Member] \| Rest of World [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									1,026,800	916,700	926,100
TYSABRI [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									900,200	776,000	588,600
TYSABRI [Member] \| UNITED STATES [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									252,800	231,800	196,400
TYSABRI [Member] \| Rest of World [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									647,400	544,200	392,200
Other products [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									51,500	54,000	48,500
Other products [Member] \| UNITED STATES [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									0
Other products [Member] \| Rest of World [Member]
Entity-Wide Information, Revenue from External Customer [Line Items]
Total product revenues									$ 51,500	$ 54,000	$ 48,500

Segment Information (Details 2) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
Segment Information (Details 2) - USD ($) $ in Thousands	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Entity-Wide Revenue, Major Customer [Line Items]
Product revenues	$ 909,800	$ 876,900	$ 859,200	$ 824,200	$ 826,800	$ 801,700	$ 791,000	$ 733,400	$ 3,470,056	$ 3,152,941	$ 2,839,651
Revenues from unconsolidated joint business									1,077,200	1,094,900	1,128,200
Other revenues from external customers	51,400	$ 41,000	$ 47,100	$ 29,700	43,600	$ 34,900	$ 26,700	$ 24,300	169,123	129,544	129,618
Long-lived assets	1,838,600				1,805,400				1,838,600	1,805,400	1,777,900
Asia [Member]
Entity-Wide Revenue, Major Customer [Line Items]
Product revenues									69,000	47,900	36,500
Revenues from unconsolidated joint business									26,000	24,100	21,700
Long-lived assets	5,400				3,600				5,400	3,600	4,200
Europe [Member]
Entity-Wide Revenue, Major Customer [Line Items]
Product revenues									1,090,700	913,700	822,600
Revenues from unconsolidated joint business									95,300	190,200	272,300
Other revenues from external customers									32,600	26,200	32,800
Long-lived assets	716,900				705,600				716,900	705,600	658,800
Other [Member]
Entity-Wide Revenue, Major Customer [Line Items]
Product revenues									203,700	178,500	153,200
Revenues from unconsolidated joint business									49,600	41,400	41,000
Long-lived assets	1,600				2,100				1,600	2,100	1,200
UNITED STATES [Member]
Entity-Wide Revenue, Major Customer [Line Items]
Product revenues									1,744,300	1,638,000	1,472,900
Revenues from unconsolidated joint business									906,300	839,200	793,200
Other revenues from external customers									136,000	102,800	96,500
Long-lived assets	1,113,400				1,092,700				1,113,400	1,092,700	1,111,200
GERMANY [Member]
Entity-Wide Revenue, Major Customer [Line Items]
Product revenues									362,400	374,800	354,500
Other revenues from external customers									500	500	300
Long-lived assets	$ 1,500				$ 1,400				$ 1,500	$ 1,400	$ 2,500

Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2009	Sep. 30, 2009	Jun. 30, 2009	Mar. 31, 2009	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Quarterly Financial Data (Unaudited)
Product revenues	$ 909,800	$ 876,900	$ 859,200	$ 824,200	$ 826,800	$ 801,700	$ 791,000	$ 733,400	$ 3,470,056	$ 3,152,941	$ 2,839,651
Unconsolidated joint business revenues	258,000	258,000	306,400	254,900	256,600	283,900	275,600	278,800	1,077,244	1,094,863	1,128,238
Other revenues	51,400	41,000	47,100	29,700	43,600	34,900	26,700	24,300	169,123	129,544	129,618
Total revenues	1,219,000	1,175,800	1,212,700	1,108,900	1,127,000	1,120,500	1,093,300	1,036,500	4,716,423	4,377,348	4,097,507
Gross Profit	1,118,800	1,079,900	1,105,700	1,011,800	1,027,300	1,027,000	1,002,600	938,300	4,316,200	3,995,200
Total costs and expenses and income tax expense	942,600	1,056,700	919,100	880,500	827,400	850,300	963,100	796,800	3,798,900	3,437,500
Other income (expense), net	(4,700)	(6,900)	1,000	(8,400)	6,400	9,400	14,700	6,800	(18,983)	37,252	(57,728)
Net income	271,800	112,200	294,600	220,000	306,000	279,600	144,900	246,600	898,573	977,062	790,107
Net income attributable to noncontrolling interest, net of tax	31,500	(141,900)	1,200	2,600	400	1,900	2,000	2,600	(106,700)	6,930	6,940
Net income (loss) attributable to Biogen Idec Inc.	$ 240,300	$ 254,100	$ 293,400	$ 217,400	$ 305,600	$ 277,700	$ 142,800	$ 244,000	$ 1,005,273	$ 970,132	$ 783,167
Basic earnings per share attributable to Biogen Idec Inc.	$ 1.00	$ 1.06	$ 1.13	$ 0.80	$ 1.07	$ 0.96	$ 0.49	$ 0.85	$ 3.98	$ 3.37	$ 2.67
Diluted earnings per share attributable to Biogen Idec Inc.	$ 0.99	$ 1.05	$ 1.12	$ 0.80	$ 1.06	$ 0.95	$ 0.49	$ 0.84	$ 3.94	$ 3.35	$ 2.65
Quarterly Financial Data (Unaudited) (Textuals) [Abstract]
Development expense									$ 271,376		$ 25,000
Reduction to income tax expense					$ 34,000			$ 30,200
Expenses related to restructuring plan included in total cost and expenses									3,467,534	$ 3,081,921	$ 2,883,896
Restructuring Plan [member]
Quarterly Financial Data (Unaudited) (Textuals) [Abstract]
Expenses related to restructuring plan included in total cost and expenses	$ 75,200
Genentech [Member]
Quarterly Financial Data (Unaudited) (Textuals) [Abstract]
Development expense	10,000
Cardiokine Biopharma [Member]
Quarterly Financial Data (Unaudited) (Textuals) [Abstract]
Development expense	$ 25,000
Acorda [Member]
Quarterly Financial Data (Unaudited) (Textuals) [Abstract]
Payment related to collaboration and license agreement							$ 110,000
Knopp [Member]
Quarterly Financial Data (Unaudited) (Textuals) [Abstract]
Development expense		$ 205,000
Collaboration and license expense attribution to the noncontrolling interest									$ 145,000
Biogen Idec Hemophilia [Member]
Quarterly Financial Data (Unaudited) (Textuals) [Abstract]
Development expense				$ 40,000

Subsequent Events (Details)	12 Months Ended
Subsequent Events (Details)	Dec. 31, 2010
San Diego Facility [Member]
Long-term Purchase Commitment [Line Items]
Sale - Leaseback transaction period in months	15