View Filing Data

Document and Entity Information - USD ($)	9 Months Ended
Document and Entity Information - USD ($)	Sep. 30, 2010	Oct. 22, 2010	Jun. 30, 2010
Document and Entity Information [Abstract]
Entity Registrant Name	BIOGEN IDEC INC.
Entity Central Index Key	0000875045
Document Type	10-Q
Document Period End Date	Sep. 30, 2010
Amendment Flag	false
Document Fiscal Year Focus	2010
Document Fiscal Period Focus	Q3
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		238,302,269

Consolidated Statements of Income (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2010	Sep. 30, 2009
Revenues:
Product	$ 876,850	$ 801,689	$ 2,560,305	$ 2,326,067
Unconsolidated joint business	257,981	283,919	819,281	838,307
Other	40,958	34,910	117,765	85,918
Total revenues	1,175,789	1,120,518	3,497,351	3,250,292
Costs and expenses:
Cost of sales, excluding amortization of acquired intangible assets	95,918	93,486	299,958	282,404
Research and development	319,054	304,055	957,759	999,986
Selling, general and administrative	244,160	226,755	755,147	669,415
Collaboration profit sharing	63,991	60,697	190,240	152,608
Amortization of acquired intangible assets	53,531	51,347	155,568	233,830
Acquired in-process research and development	205,000		244,976
Total costs and expenses	981,654	736,340	2,603,648	2,338,243
Income from operations	194,135	384,178	893,703	912,049
Other income (expense), net	(6,945)	9,360	(14,318)	30,886
Income before income tax expense	187,190	393,538	879,385	942,935
Income tax expense	75,011	113,936	252,564	271,869
Net income	112,179	279,602	626,821	671,066
Net income (loss) attributable to noncontrolling interest, net of tax	(141,936)	1,939	(138,174)	6,571
Net income attributable to Biogen Idec Inc.	$ 254,115	$ 277,663	$ 764,995	$ 664,495
Net income per share:
Basic earnings per share attributable to Biogen Idec Inc.	$ 1.06	$ 0.96	$ 2.98	$ 2.3
Diluted earnings per share attributable to Biogen Idec Inc.	$ 1.05	$ 0.95	$ 2.95	$ 2.28
Weighted-average shares used in calculating:
Basic earnings per share attributable to Biogen Idec Inc.	239,864	288,917	256,586	288,416
Diluted earnings per share attributable to Biogen Idec Inc.	242,313	291,037	258,906	290,368

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2010	Dec. 31, 2009
Current assets:
Cash and cash equivalents	$ 626,757	$ 581,889
Marketable securities	197,835	681,835
Accounts receivable, net	616,697	551,208
Due from unconsolidated joint business	221,618	193,789
Inventory	269,313	293,950
Other current assets	198,911	177,924
Total current assets	2,131,131	2,480,595
Marketable securities	560,006	1,194,080
Property, plant and equipment, net	1,641,791	1,637,083
Intangible assets, net	1,715,342	1,871,078
Goodwill	1,138,621	1,138,621
Investments and other assets	207,256	230,397
Total assets	7,394,147	8,551,854
Current liabilities:
Accounts payable	143,699	118,534
Taxes payable	115,689	75,891
Accrued expenses and other	553,796	500,755
Current portion of notes payable and line of credit	11,296	19,762
Total current liabilities	824,480	714,942
Notes payable and line of credit	1,068,776	1,080,207
Long-term deferred tax liability	174,615	240,618
Other long-term liabilities	256,075	254,205
Total liabilities	$ 2,323,946	$ 2,289,972
Commitments and contingencies (Notes 9, 14, 16, 17 and 18)
Shareholders' 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	3,855,690	5,781,920
Accumulated other comprehensive income	(9,161)	50,496
Retained earnings	1,646,852	1,068,890
Treasury stock, at cost	(462,810)	(679,920)
Total Biogen Idec Inc. shareholders' equity	5,030,695	6,221,530
Noncontrolling interest	39,506	40,352
Total shareholders' equity	5,070,201	6,261,882
Total liabilities and shareholders' equity	$ 7,394,147	$ 8,551,854

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2010	Sep. 30, 2009
Cash flows from operating activities:
Net income	$ 626,821	$ 671,066
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization of property, plant and equipment and intangible assets	260,089	334,761
Acquired in-process research and development	271,376
Share-based compensation	134,594	119,902
Non-cash interest (income) expense and foreign exchange remeasurement loss (gain), net	1,124	(12,861)
Deferred income taxes	(61,244)	(72,580)
Realized gain on sale of marketable securities and strategic investments	(16,113)	(17,185)
Write-down of inventory to net realizable value	9,918	13,431
Loss on disposal of property, plant and equipment, net	1,748
Impairment of marketable securities, investments and other assets	19,319	9,866
Excess tax benefit from share-based compensation	(6,284)	(3,194)
Changes in operating assets and liabilities, net:
Accounts receivable	(72,719)	(96,215)
Due from unconsolidated joint business	(27,829)	13,646
Inventory	16,311	(25,195)
Other assets	(22,435)	8,555
Accrued expenses and other current liabilities	17,377	(37,733)
Other liabilities and taxes payable	41,564	(110,706)
Net cash flows provided by operating activities	1,193,617	795,558
Cash flows from investing activities:
Purchases of marketable securities	(1,371,769)	(3,001,156)
Proceeds from sales and maturities of marketable securities	2,490,363	2,334,093
Acquisitions	(39,976)
Acquisition of a variable interest entity, net	(84,952)
Purchases of property, plant and equipment	(124,220)	(110,129)
Purchases of other investments	(5,499)	(36,519)
Proceeds from the sale of a strategic equity investment		6,067
Collateral received under securities lending		29,991
Net cash flows provided by (used in) investing activities	863,947	(777,653)
Cash flows from financing activities:
Purchases of treasury stock	(2,077,579)	(57,631)
Proceeds from issuance of stock for share-based compensation arrangements	80,447	33,236
Change in cash overdraft	2,586	7,497
Net distributions to noncontrolling interest	(6,401)	(2,832)
Excess tax benefit from share-based compensation	6,284	3,194
Repayment of borrowings	(16,182)	(10,867)
Obligation under securities lending		(29,991)
Net cash flows used in financing activities	(2,010,845)	(57,394)
Net increase in cash and cash equivalents	46,719	(39,489)
Effect of exchange rate changes on cash and cash equivalents	(1,851)	2,892
Cash and cash equivalents, beginning of the period	581,889	622,385
Cash and cash equivalents, end of the period	$ 626,757	$ 585,788

Overview

9 Months Ended

Sep. 30, 2010

Overview [Abstract]

Overview


1.	Overview

Biogen Idec is a global biotechnology company that discovers, develops, manufactures and commercializes innovative therapies for human health care. 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.

Basis of Presentation

In the opinion of management, the accompanying unaudited consolidated financial statements include all adjustments, consisting of normal recurring accruals, necessary for a fair presentation of our financial statements for interim periods in accordance with accounting principles generally accepted in the United States (U.S. GAAP). The information included in this quarterly report on Form 10-Q should be read in conjunction with our consolidated financial statements and the accompanying notes included in our Annual Report on Form 10-K for the year ended December 31, 2009 (2009 Form 10-K). Our accounting policies are described in the “Notes to Consolidated Financial Statements” in our 2009 Form 10-K and updated, as necessary, in this Form 10-Q. The year-end consolidated balance sheet data presented for comparative purposes was derived from audited financial statements, but does not include all disclosures required by U.S. GAAP. The results of operations for the three and nine months ended September 30, 2010 are not necessarily indicative of the operating results for the full year or for any other subsequent interim period.

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.

In determining whether we are the primary beneficiary of an entity, we consider a number of factors, including our ability to direct the activities that most significantly affect the entity’s economic success, our contractual rights and responsibilities under the arrangement and the significance of the arrangement to each party. These considerations impact the way we account for our existing collaborative and joint venture relationships and determines the consolidation of companies or entities with which we have collaborative or 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, including those related to revenue recognition and related allowances, marketable securities, derivatives and hedging activities, inventory, impairments of long-lived assets including intangible assets, impairments of goodwill, the consolidation of variable interest entities, income taxes including the valuation allowance for deferred tax assets, valuation of investments, research and development expenses, contingencies and litigation, and share-based payments. 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.

Subsequent Events

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


	•	On October 1, 2010, we sold our San Diego campus for cash proceeds of approximately $128.0 million. As part of this transaction, we have also agreed to leaseback all of the San Diego facilities for a period of 15 months. We will account for this transaction as a financing arrangement. For a more detailed description of these transactions, please read Note 9, Property, Plant and Equipment.

	•	On October 19, 2010, we and Genentech, Inc., a member of the Roche Group (Genentech), amended and restated our Amended and Restated Collaboration Agreement dated June 19, 2003 with regard to the development of ocrelizumab, a humanized anti-CD20 antibody, and agreed to terms for the development of GA101, a next-generation anti-CD20 antibody. For a more detailed description of this transaction and its effect on our collaboration with Genentech, please read Note 17, Collaborations.

Revenue Recognition

9 Months Ended

Sep. 30, 2010

Revenue Recognition [Abstract]

Revenue Recognition


3.	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 collectability 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 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.

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 royalty and co-promotion profit revenue on sales of RITUXAN in the rest of world on a cash basis.

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.

Multiple-Deliverable Revenue Arrangements

During the third quarter of 2010, we elected to early adopt 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 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 as applied to all previously reported interim periods in the fiscal year of adoption. Our adoption of this standard did not have a material impact our financial position or results of operations as through the third quarter of 2010, we had not recorded any revenue in accordance with revenue recognition rules for multiple deliverables as described in ASU 2009-13 or its predecessor pronouncements.

Bad Debt Reserves

Bad debt reserves are based on our estimated uncollectible accounts receivable. Given our historical experiences with bad debts, combined with our credit management policies and practices, we do not presently maintain significant bad debt reserves.

Concentrations of Credit Risk

The majority of our accounts receivable arise from product sales in the United States and Europe and are primarily due from wholesale distributors, large pharmaceutical companies and public hospitals. 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 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 Greece, Italy, Spain, Portugal and Ireland, 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 September 30, 2010, our accounts receivable in Greece, Italy, Spain, Portugal and Ireland totaled approximately $250.4 million. To date, we have not experienced any significant losses with respect to the collection of our accounts receivable.

Reserves for Discounts and Allowances

We establish reserves for trade term discounts, wholesaler incentives, Medicaid rebates, VA and 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 purchased 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. An analysis of the amount of, and change in, reserves is summarized as follows:


				Contractual
(In millions)	Discounts			Adjustments			Returns			Total

Balance, as of December 31, 2009	$	13.9		$	70.3		$	18.9		$	103.1
Current provisions relating to sales in current year		58.0			204.7			12.3			275.0
Adjustments relating to prior years		(2.4	)		(2.2	)		(1.8	)		(6.4	)
Payments/returns relating to sales in current year		(45.9	)		(110.3	)		(0.5	)		(156.7	)
Payments/returns relating to sales in prior years		(9.5	)		(60.7	)		(9.5	)		(79.7	)

Balance, as of September 30, 2010	$	14.1		$	101.8		$	19.4		$	135.3

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


	As of		As of
	September 30,		December 31,
(In millions)	2010		2009

Reduction of accounts receivable	$	34.7	$	43.3
Current liability		100.6		59.8

Total reserves	$	135.3	$	103.1

Healthcare Reform

In March 2010, healthcare reform legislation was enacted in the U.S. This legislation contains several provisions that affect our business.

Although many provisions of the new legislation did not take effect immediately, several provisions became effective in the first quarter of 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) Public Health Services drug pricing program, which provides outpatient drugs at reduced rates, to include additional hospitals, clinics, and healthcare centers.

Beginning in 2011, the new law also requires drug manufacturers to provide a 50% discount to Medicare beneficiaries whose prescription drug costs cause them to be subject to the Medicare Part D coverage gap (i.e. the “donut hole”). Also, in 2011, a new fee will be payable by branded prescription drug manufacturers and importers. This fee will be calculated based upon each organization’s percentage share of total branded prescription drug sales to qualifying U.S. government programs (such as Medicare, Medicaid and VA and PHS discount programs) made during the previous year. The aggregated industry wide fee is expected to total $28 billion through 2019, of which $2.5 billion is payable in 2011.

This new legislation contains a number of provisions that affect existing government programs and has required the creation of new programs, policies and processes, many of which remain under development and have not been fully implemented. For example, we do not yet fully know the extent of additional entities eligible to participate under the 340(B) program or when and how discounts will be provided to these entities. In addition, the operation of the Medicare Part D coverage gap remains uncertain, though, as noted above, this program and others will not be effective until 2011.

Intangible Assets and Goodwill

9 Months Ended

Sep. 30, 2010

Intangible Assets and Goodwill [Abstract]

Intangible Assets and Goodwill


5.	Intangible Assets and Goodwill

Intangible Assets

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


			As of September 30, 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	$	(339.9	)	$	238.1	$	578.0	$	(306.0	)	$	272.0
Core developed technology		15-23 years		3,005.3		(1,593.9	)		1,411.4		3,005.3		(1,472.4	)		1,532.9
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		(2.0	)		0.1		2.1		(1.8	)		0.3
Distribution rights		2 years		12.7		(12.7	)		—		12.7		(12.7	)		—

Total intangible assets			$	3,665.1	$	(1,949.8	)	$	1,715.3	$	3,665.1	$	(1,794.0	)	$	1,871.1

Intangible assets were unchanged as of September 30, 2010, 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 September 30, 2010 was $1,396.7 million. We believe the economic benefit of our core technology is consumed as revenue is generated from our AVONEX product, which we refer to as the economic consumption amortization model. This amortization methodology 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 product sales 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 completed our most recent long range planning cycle in the third quarter of 2010. Based upon this analysis, we have continued to amortize this asset on the economic consumption model for the third quarter of 2010, and expect to apply the same model for the subsequent three quarters. In addition, this analysis did not result in a significant change in the expected lifetime revenue of AVONEX. As a result, the amortization recorded in relation to our core intangible asset for the current and three subsequent quarters is anticipated to be comparable to amounts recorded during the prior four quarters. We monitor events and expectations on product performance. 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.

For the three and nine months ended September 30, 2010, amortization for acquired intangible assets totaled $53.5 million and $155.6 million, respectively, compared to $51.3 million and $233.8 million, respectively, in the prior year comparative periods and is expected to be in the range of approximately $170.0 million to $210.0 million annually through 2015.

Goodwill

Our goodwill balance remained unchanged as of September 30, 2010, compared to December 31, 2009. As of September 30, 2010, we had no accumulated impairment losses.

Fair Value Measurements

9 Months Ended

Sep. 30, 2010

Fair Value Measurements [Abstract]

Fair Value Measurements


6.	Fair Value Measurements

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 clarifies existing disclosure requirements related to the level of disaggregation of fair value measurements for each class of assets and liabilities and disclosures about inputs and valuation techniques used to measure fair value for both recurring and nonrecurring Level 2 and Level 3 measurements. 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. In addition, effective for interim and annual periods beginning after December 15, 2010, this standard will require additional disclosure and require an entity to present disaggregated information about activity in Level 3 fair value measurements on a gross basis, rather than as one net amount.

The tables below present information about our assets and liabilities that are measured at fair value on a recurring basis as of September 30, 2010 and December 31, 2009, and indicate the fair value hierarchy of the valuation techniques we utilized to determine such fair value. In general, fair values determined by Level 1 inputs utilize quoted prices (unadjusted) in active markets for identical assets or liabilities. Fair values determined by Level 2 inputs utilize data points from active markets that are observable, such as quoted prices, interest rates and yield curves. Fair values determined by Level 3 inputs utilize unobservable data points for the asset or liability.

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 September 30, 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.

Our venture capital investments include investments in certain biotechnology oriented venture capital funds which primarily invest in small privately-owned, venture-backed biotechnology companies. These investments are the only assets for which we used Level 3 inputs to determine the fair value and represented approximately 0.3% of total assets as of both September 30, 2010 and December 31, 2009. 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. Gains and losses (realized and unrealized) included in earnings for the period are reported in other income (expense), net.

There have been no transfers of assets or liabilities between the fair value measurement classifications for all periods presented.

The following tables set forth our financial assets and liabilities that were recorded at fair value:


							Significant
	Balance as of		Quoted Prices in		Significant Other		Unobservable
	September 30,		Active Markets		Observable Inputs		Inputs
(In millions)	2010		(Level 1)		(Level 2)		(Level 3)

Assets:
Cash equivalents	$	534.3	$	—	$	534.3	$	—
Marketable debt securities:
Corporate debt securities		226.3		—		226.3		—
Government securities		476.0		—		476.0		—
Mortgage and other asset backed securities		55.5		—		55.5		—
Strategic investments		36.4		36.4		—		—
Venture capital investments		21.8		—		—		21.8
Derivative contracts		1.0		—		1.0		—
Plan assets for deferred compensation		12.3		—		12.3		—

Total	$	1,363.6	$	36.4	$	1,305.4	$	21.8

Liabilities:
Derivative contracts	$	24.5	$	—	$	24.5	$	—

Total	$	24.5	$	—	$	24.5	$	—


							Significant
	Balance as of		Quoted Prices in		Significant Other		Unobservable
	December 31,		Active Markets		Observable 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	$	—

The following table provides a roll forward of the fair value of our venture capital investments, where fair value is determined by Level 3 inputs:


	For the Three Months				For the Nine Months
	Ended September 30,				Ended September 30,
(In millions)	2010		2009		2010			2009

Beginning balance	$	20.4	$	21.6	$	21.9		$	23.9
Total net unrealized gains (losses) included in earnings		0.5		0.9		(1.1	)		(2.2	)
Net purchases, issuances, and settlements		0.9		0.6		1.0			1.4

Ending balance	$	21.8	$	23.1	$	21.8		$	23.1

The fair and carrying value of our debt instruments are summarized as follows:


	As of September 30, 2010				As of December 31, 2009
	Fair		Carrying		Fair		Carrying
(In millions)	Value		Value		Value		Value

Credit line from Dompé	$	10.3	$	10.2	$	17.2	$	17.2
Notes payable to Fumedica		23.6		20.9		31.3		30.0
6.0% Senior Notes due 2013		493.6		449.7		475.7		449.6
6.875% Senior Notes due 2018		646.8		599.3		589.1		603.2

Total	$	1,174.3	$	1,080.1	$	1,113.3	$	1,100.0

The fair values of our credit line from Dompé and our note payable to Fumedica were estimated using an income-based approach with market observable inputs including current interest and foreign currency exchange rates. The fair value of our Senior Notes was determined through a market-based approach using observable and corroborated sources; within the hierarchy of fair value measurements, these are classified as Level 2 fair values.

Financial Instruments

9 Months Ended

Sep. 30, 2010

Financial Instruments [Abstract]

Financial Instruments


7.	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 September 30, 2010 (In millions):	Value		Gains		Losses			Cost

Available-for-sale
Corporate debt securities
Current	$	55.3	$	0.1	$	—		$	55.2
Non-current		171.0		3.3		(0.1	)		167.8
Government securities
Current		142.4		0.2		—			142.2
Non-current		333.6		1.3		(0.1	)		332.4
Mortgage and other asset backed securities
Current		0.1		—		—			0.1
Non-current		55.4		0.4		(0.2	)		55.2

Total available-for-sale securities	$	757.8	$	5.3	$	(0.4	)	$	752.9

Other Investments
Strategic investments, non-current	$	36.4	$	7.2	$	—		$	29.2


			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 September 30, 2010 and December 31, 2009, government securities included $127.2 million and $298.8 million, respectively, of Federal Deposit Insurance Corporation (FDIC) guaranteed senior notes issued by financial institutions under the Temporary Liquidity Guarantee Program.

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 September 30, 2010 and December 31, 2009, the commercial paper, including accrued interest, had fair and carrying values of $148.5 million and $76.9 million, respectively, and short-term debt securities had fair and carrying values of $385.8 million and $399.5 million, respectively.

Summary of Contractual Maturities: Available-for-Sale Securities

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


	As of September 30, 2010				As of December 31, 2009
	Estimated		Amortized		Estimated		Amortized
(In millions)	Fair Value		Cost		Fair Value		Cost

Due in one year or less	$	168.2	$	167.9	$	522.0	$	519.5
Due after one year through five years		545.9		541.6		1,143.7		1,133.4
Due after five years		43.7		43.4		210.2		207.6

Total	$	757.8	$	752.9	$	1,875.9	$	1,860.5

The weighted average maturity of our marketable securities as of September 30, 2010 and December 31, 2009 was 13 months and 15 months, respectively.

Proceeds from Marketable Securities, excluding Strategic Investments

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


	For the Three Months				For the Nine Months
	Ended September 30,				Ended September 30,
(In millions)	2010		2009		2010		2009

Proceeds from maturities and sales	$	487.8	$	696.5	$	2,490.4	$	2,334.1
Realized gains	$	5.0	$	3.1	$	18.1	$	17.0
Realized losses	$	0.2	$	1.3	$	2.0	$	3.4

Realized losses for the three and nine months ended September 30, 2010, primarily relate to the sale of agency mortgage-backed securities and corporate debt securities. The realized losses for the three and nine months ended September 30, 2009, primarily relate to losses on the sale of corporate debt securities and non-agency mortgage-backed securities.

Impairments

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 debt 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 recorded 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 and are recorded within earnings as an impairment loss.

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 recorded within earnings as an impairment loss.

Recognition and Measurement of Other-than-Temporary Impairment

For the three and nine months ended September 30, 2010, we recognized $2.8 million and $19.8 million, respectively, in charges for the other-than-temporary impairment of our publicly held strategic investments, investments in venture capital funds and investments in privately-held companies compared to $0.5 million and $6.5 million in the prior year comparative periods. The increase for the nine month comparative periods was primarily due to AVEO Pharmaceuticals, Inc., one of our strategic investments, executing an equity offering at a price below our cost basis during the first quarter of 2010.

We recognized $3.6 million in other-than-temporary impairment charges on our marketable debt securities during the nine months ended September 30, 2009. No impairments were recognized related to our marketable debt securities for the three months ended September 30, 2009 or for the three and nine months ended September 30, 2010.

Derivative Instruments

9 Months Ended

Sep. 30, 2010

Derivative Instruments [Abstract]

Derivative Instruments


8.	Derivative Instruments

Our primary market exposure is to changes (or fluctuations) in foreign exchange rates. We use certain derivative instruments to help manage this exposure. We execute these instruments with financial institutions we judge to be creditworthy and the majority of the foreign currencies are denominated in currencies of major industrial countries. We do not hold or issue derivative instruments for trading or speculative purposes.

We recognize all derivative instruments as either assets or liabilities at fair value in our consolidated balance sheets. We classify the cash flows from these instruments in the same category as the cash flows from the hedged items.

Foreign Currency Forward Contracts

Due to the global nature of our operations, portions of our revenues are earned in currencies other than the U.S. dollar. The value of revenues measured in U.S. dollars is subject to changes in currency exchange rates. In order to mitigate these changes we use foreign currency forward contracts to lock in exchange rates.

Foreign currency forward contracts in effect as of September 30, 2010 and December 31, 2009 had remaining durations of 1 to 13 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. 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		As of
	September 30,		December 31,
Foreign Currency: (In millions)	2010		2009

Euro	$	511.6	$	495.9
Canadian Dollar		29.6		22.3

Total	$	541.2	$	518.2

The portion of the fair value of these foreign currency forward contracts that was included in accumulated other comprehensive income within total equity reflected net losses of $17.1 million and net gains of $1.2 million as of September 30, 2010 and December 31, 2009, respectively. We expect all contracts to be settled over the next 13 months and any amounts in accumulated other comprehensive income 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 September 30, 2010 and December 31, 2009, credit risk did not materially change the fair value of our forward contracts.

For the three and nine months ended September 30, 2010, we recognized $20.7 million and $40.6 million, respectively, of gains in product revenue for the settlement of certain effective cash flow hedge forward contracts compared to losses recognized in the amount of $16.3 million and $28.6 million, respectively, in the prior year comparative periods. These settlements were recorded in the same period as the related forecasted revenue.

In relation to our foreign currency forward contracts, we recognized in earnings net gains of $1.4 million and $0.9 million, respectively, due to hedge ineffectiveness for the three and nine months ended September 30, 2010. We recognized net losses of $0.1 million and $0.9 million, respectively, in the prior year comparative periods.

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 as of September 30, 2010 and December 31, 2009:

Foreign Currency Forward Contracts

Asset Derivatives

Liability Derivatives

(In millions)

Balance Sheet Location

Fair Value

Balance Sheet Location

Fair Value

September 30, 2010

Other Current Assets

—

Accrued Expenses and Other

16.5

December 31, 2009

Other Current Assets

10.8

Accrued Expenses and Other

9.8

The following table summarizes the effect of derivatives designated as hedging instruments on the consolidated statements of income for the three and nine months ended September 30, 2010 and 2009:

Amount

Recognized in

Reclassified from

Accumulated

Other

Comprehensive

Income

Amount of

on Derivative

Statement

into Income

Statement

Gain/(Loss)

Location

Gain/(Loss)

Location

Recorded

(In millions)

(Effective Portion)

(Ineffective Portion)

For the Three Months Ended

September 30, 2010:

Foreign currency contracts

(17.1

)

Revenue

20.7

Other income (expense)

1.4

September 30, 2009:

Foreign currency contracts

(34.7

)

Revenue

(16.3

)

Other income (expense)

(0.1

)

For the Nine Months Ended

September 30, 2010:

Foreign currency contracts

(17.1

)

Revenue

40.6

Other income (expense)

0.9

September 30, 2009:

Foreign currency contracts

(34.7

)

Revenue

(28.6

)

Other income (expense)

(0.9

)

Other Derivatives

We enter into other foreign currency forward contracts, 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. As of September 30, 2010, the aggregate notional amount of our outstanding foreign currency contracts was $170.1 million. The fair value of these contracts was a net liability of $7.0 million. Net losses of $10.1 million and net gains of $3.0 million related to these contracts were recognized as a component of other income (expense), net, for the three and nine months ended September 30, 2010, respectively. We recognized net losses of $2.2 million and a de minimis amount, respectively, as a component of other income (expense), net for the three and nine months ended September 30, 2009.

Share-based Payments

9 Months Ended

Sep. 30, 2010

Share-based Payments [Abstract]

Share-based Payments


13.	Share-based Payments

Share-based Compensation Expense

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


	For the Three Months						For the Nine Months
	Ended September 30,						Ended September 30,
(In millions)	2010			2009			2010			2009

Research and development	$	15.9		$	15.6		$	48.0		$	46.0
Selling, general and administrative		26.9			27.2			97.1			78.7

Subtotal		42.8			42.8			145.1			124.7
Capitalized share-based payment costs		(0.9	)		(1.7	)		(2.5	)		(4.8	)

Share-based compensation expense included in total costs and expenses		41.9			41.1			142.6			119.9
Income tax effect		(13.0	)		(12.6	)		(45.4	)		(36.8	)

Share-based compensation expense included in net income attributable to Biogen Idec	$	28.9		$	28.5		$	97.2		$	83.1

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


	For the Three Months						For the Nine Months
	Ended September 30,						Ended September 30,
(In millions)	2010			2009			2010			2009

Stock options	$	3.0		$	5.5		$	23.1		$	16.6
Market stock units		2.3			—			7.8			—
Time-vested restricted stock units		30.8			34.4			96.5			99.9
Performance-vested restricted stock units settled in shares		0.7			(0.3	)		4.4			3.0
Performance-vested restricted stock units settled in cash		2.7			—			8.0			—
Employee stock purchase plan		3.3			3.2			5.3			5.2

Subtotal	$	42.8		$	42.8		$	145.1		$	124.7
Capitalized share-based payment costs		(0.9	)		(1.7	)		(2.5	)		(4.8	)

Share-based compensation expense included in total costs and expenses	$	41.9		$	41.1		$	142.6		$	119.9

Stock Options

For the nine months ended September 30, 2010, approximately 124,000 stock options were granted with a weighted average exercise price of $57.38 and weighted average grant date fair value of $16.52, compared to approximately 1.0 million stock options granted in the prior year comparative period with a weighted average exercise price of $50.02 and weighted average grant date fair value of $18.01. The fair values of our stock option grants are estimated as of the date of grant using the Black-Scholes option valuation model. The estimated fair values of the stock options, including the effect of estimated forfeitures, are then expensed over the options’ requisite service period, which is typically the vesting period.

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

For the nine months ended September 30, 2010, approximately 400,000 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 expected 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

We apply a graded vesting expense methodology when accounting for 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.

Cash Settled Performance Shares

For the nine months ended September 30, 2010, approximately 378,000 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 ends 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.

We apply a graded vesting expense methodology when accounting for the 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 CSPS awards 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.

Time-Vested Restricted Stock Units (RSUs)

For the nine months ended September 30, 2010, approximately 2.0 million RSUs were granted with a weighted average grant date fair value of $54.63, compared to approximately 2.5 million RSUs granted in the prior year comparative period with a weighted average grant date fair value of $49.35. The fair values of our RSUs are based on the market value of our stock on the date of grant and are recognized over the applicable service period, adjusted for the effect of estimated forfeitures.

Performance-Vested Restricted Stock Units (PVRSUs)

For the nine months ended September 30, 2009, approximately 321,000 PVRSUs were granted with a weighted average grant date fair value of $49.46. The number of PVRSUs earned was subject to the attainment of certain performance criteria during 2009. Based on our 2009 performance, 99% of the granted PVRSUs were earned. These awards 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, and are also subject to the respective employee’s continued employment.

We apply a graded vesting expense methodology when accounting for our PVRSUs. Compensation expense associated with PVRSU awards 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.

Employee Stock Purchase Plan (ESPP)

For the nine months ended September 30, 2010, approximately 457,000 shares were issued under the ESPP compared to approximately 426,000 shares issued in the prior year comparative period.

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 the 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.

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

9 Months Ended

Sep. 30, 2010

Income Taxes [Abstract]

Income Taxes


14.	Income Taxes

For the three and nine months ended September 30, 2010, our effective worldwide income tax rates were 40.1% and 28.7%, respectively, compared to 29.0% and 28.8% in the prior year comparative periods.

Our effective tax rate for the three and nine months ended September 30, 2010, was negatively impacted due to the attribution to noncontrolling interest of $145.0 million of the IPR&D charge related to our collaboration and license agreement with Knopp Neurosciences, Inc. As such, the attributed amount will not generate a tax deduction, causing our tax rate to be unfavorably impacted by 13.5% and 2.7%, respectively. The impact of the Knopp transaction was partially offset by a higher percentage of our profits being earned in lower rate international jurisdictions in 2010. This change in the location of our relative profits was caused by the growth of our international operations and lower 2010 domestic earnings as a proportion of total consolidated earnings due, in part, to the U.S. healthcare reform legislation enacted in March 2010. For a more detailed description of our transaction with Knopp, please read Note 16, Investments in Variable Interest Entities.

During 2010, we also experienced a favorable impact on our effective tax rates due to a statutory increase in the U.S. manufacturers’ tax deduction and an increase in expenditures eligible for our orphan drug credit. The favorable impact of these items were offset by the expiration of the federal research and development tax credit which was not in effect for the nine months ended September 30, 2010. In addition, our 2009 effective tax rate for the three and nine months ended September 30, 2009 was increased by 2.4% and 2.3%, respectively, as a result of the $110.0 million upfront payment incurred in connection with the collaboration and license agreement entered into with Acorda Therapeutics, Inc. (Acorda) in the second quarter of 2009. Our effective tax rate for the nine months ended September 30, 2009 was also favorably impacted by 3.2% for changes in tax law which became effective during the first quarter of 2009 in certain state jurisdictions in which we operate.

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


	For the Three Months						For the Nine Months
	Ended September 30,						Ended September 30,
	2010			2009			2010			2009

Statutory rate		35.0	%		35.0	%		35.0	%		35.0	%
State taxes		2.4			2.2			2.0			1.6
Taxes on foreign earnings		(13.6	)		(7.7	)		(10.8	)		(5.8	)
Credits and net operating loss utilization		(4.3	)		(1.5	)		(2.2	)		(4.1	)
Purchased intangible assets		2.9			0.9			1.8			2.0
IPR&D		21.6			0.9			5.2			1.1
Permanent items		(3.8	)		(1.0	)		(2.1	)		(1.5	)
Other		(0.1	)		0.2			(0.2	)		0.5

Effective tax rate		40.1	%		29.0	%		28.7	%		28.8	%

Accounting for Uncertainty in Income Taxes

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.

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, the computation of BIMA’s research and development credits and the availability of certain claimed deductions 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 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. 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.

Investments in Variable Interest Entities

9 Months Ended

Sep. 30, 2010

Investments in Variable Interest Entities [Abstract]

Investments in Variable Interest Entities


16.	Investments in Variable Interest Entities

Effective January 1, 2010, we adopted a newly issued accounting standard which provides 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. 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. The adoption of this standard did not have an impact on our financial position or results of operations. 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.

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 described in our 2009 Form 10-K, have no recourse to Biogen Idec.

Included within our consolidated balance sheet at September 30, 2010 are total joint venture assets and liabilities of $167.1 million and $75.1 million, respectively. The joint venture’s most significant assets are accounts receivable from the ordinary course of business of $118.5 million.

We have provided no financing to these joint ventures other than previously contractually required amounts.

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 KNS-760704 (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 and our investment in 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 and our investment in 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 earnings for the three and nine months ended September 30, 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 costs 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 Three Months				For the Nine Months
	Ended September 30,				Ended September 30,
(In millions)	2010		2009		2010		2009

Total upfront payments made to Knopp	$	26.4	$	—	$	26.4	$	—
Total development expense incurred in the development of dexpramipexole	$	1.0	$	—	$	1.0	$	—
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	27.4	$	—	$	27.4	$	—

We have provided no financing to Knopp other than the contractually required amounts disclosed above.

Neurimmune

We have a collaboration agreement with Neurimmune SubOne AG (Neurimmune), a subsidiary of Neurimmune Therapeutics 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 control the activities of the collaboration and are required to fund 100% of the research and development costs incurred in support of the collaboration agreement. As such, we consolidate the results of Neurimmune. 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 expense incurred in support of the collaboration that we reimburse 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 Three Months				For the Nine Months
	Ended September 30,				Ended September 30,
(In millions)	2010		2009		2010		2009

Milestone payments made to Neurimumune	$	—	$	—	$	—	$	7.5
Total development expense incurred by the collaboration	$	2.4	$	1.9	$	12.8	$	5.5
Total expense reflected within our consolidated statements of income	$	2.4	$	1.9	$	12.8	$	13.0

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

Cardiokine

We collaborate with Cardiokine Biopharma LLC (Cardiokine), a subsidiary of Cardiokine Inc., on the joint development of Lixivaptan, an oral compound for the potential treatment of hyponatremia in patients with congestive heart failure. Based upon our current development plans, we may pay up to $100.0 million in remaining development milestone payments, as well as royalties on commercial sales under the terms of our collaboration agreement.

We have determined that we are the primary beneficiary of Cardiokine because we control the activities of the collaboration and are required to fund 90% of the development costs under the collaboration agreement. As such, we consolidate the results of Cardiokine. The assets and liabilities of Cardiokine are 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 reimburse 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 Three Months				For the Nine Months
	Ended September 30,				Ended September 30,
(In millions)	2010		2009		2010		2009

Milestone payments made to Cardiokine	$	—	$	20.0	$	—	$	20.0
Total development expense incurred by the collaboration	$	10.9	$	17.2	$	47.4	$	48.5
Biogen Idec’s share of expense reflected within our consolidated statements of income	$	9.8	$	35.5	$	42.7	$	63.7
Collaboration expense allocated to noncontrolling interests, net of tax	$	1.1	$	1.7	$	4.7	$	4.8

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

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.

As of September 30, 2010 the total carrying value of our investments in biotechnology companies that we have determined to be variable interest entities is $22.7 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 September 30, 2010, we have recorded a receivable of $7.9 million related to a cost sharing arrangement with one of our collaborative relationships.

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

Collaborations

9 Months Ended

Sep. 30, 2010

Collaborations [Abstract]

Collaborations


17.	Collaborations

On October 19, 2010, we and Genentech amended and restated our Amended and Restated Collaboration Agreement dated June 19, 2003 with regard to the development of ocrelizumab, a humanized anti-CD20 antibody, and agreed to terms for the development of GA101, a next-generation anti-CD20 antibody, as summarized below.

Ocrelizumab

Genentech will have responsibility for the further development and commercialization of ocrelizumab in MS and will fund all of the related costs going forward. We will be entitled to receive tiered royalties between 13.5% and 24% on U.S. sales of ocrelizumab. Commercialization of ocrelizumab will not impact our percentage of the co-promotion profits for RITUXAN.

GA101

We will increase our share of the losses and profits related to the development and commercialization of GA101 in the U.S. 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. To date, we had paid 30% of the GA101 development expenses. We will pay 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

Our current pretax co-promotion profit-sharing formula, which resets annually, provides for a 30% share of the first $50.0 million of co-promotion operating profits for RITUXAN in the U.S. and Canada and a 40% share of such profits in excess of $50.0 million. 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 CCL.

	•	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 reach $150.0 million or (2) the first day of the calendar quarter following the date following 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.

For a description of terms, conditions and activities related to our other collaborative arrangements, please read Note 17, Collaborations to our consolidated financial statements included within our 2009 Form 10-K.

Litigation

9 Months Ended

Sep. 30, 2010

Litigation [Abstract]

Litigation


18.	Litigation

Along with several other major pharmaceutical and biotechnology companies, Biogen, Inc. (now BIMA) or, in some cases, Biogen Idec Inc. was named as a defendant in lawsuits filed by the City of New York and numerous Counties of the State of New York. All of the cases — except for cases filed by the County of Erie, County of Oswego and County of Schenectady (Three County Actions) — are the subject of a Consolidated Complaint, first filed on September 15, 2005 in the U.S. District Court for the District of Massachusetts in Multi-District Litigation No. 1456 (MDL proceedings). The complaints allege that the defendants (i) fraudulently reported (or caused others to report incorrectly) the Average Wholesale Price for certain drugs for which Medicaid provides reimbursement (Covered Drugs); (ii) marketed and promoted the sale of Covered Drugs to providers based on the providers’ ability to collect inflated payments from the government and Medicaid beneficiaries that exceeded payments possible for competing drugs; (iii) provided financing incentives to providers to over-prescribe Covered Drugs or to prescribe Covered Drugs in place of competing drugs; and (iv) overcharged Medicaid for illegally inflated Covered Drugs reimbursements. Among other things, the complaints allege violations of New York state law and advance common law claims for unfair trade practices, fraud, and unjust enrichment. In addition, the amended Consolidated Complaint alleges that the defendants failed to accurately report the “best price” on the Covered Drugs to the Secretary of Health and Human Services pursuant to rebate agreements, and excluded from their reporting certain discounts and other rebates that would have reduced the “best price.” With respect to the MDL proceedings, some of the plaintiffs’ claims were dismissed, and the parties, including Biogen Idec, began a mediation of the outstanding claims on July 1, 2008. On October 21, 2010, we reached a non-material out-of-court resolution of all outstanding claims against us, and the plaintiffs have agreed to dismiss the complaints as to us.

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, the computation of BIMA’s research and development credits and the availability of certain claimed deductions 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 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 27, 2008, Sanofi-Aventis Deutschland GmbH (Sanofi) 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 U.S. Patents 5,849,522 (’522 patent) and 6,218,140 (’140 patent). 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, Sanofi-Aventis U.S. LLC, and Sanofi-Aventis U.S., Inc. 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. (Sanofi-Aventis U.S. LLC and Sanofi-Aventis U.S., Inc. were later dismissed voluntarily.) 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,” and do not express an opinion at this time as to the likely outcome of the matters or as to the magnitude or range of any potential loss. We believe that we have good and valid defenses and are vigorously defending against the allegations.

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 between Hoechst’s predecessor and Genentech that pertained to the above-referenced patents and related patents outside the U.S. 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 RITUXAN, could total $100 million based on the 0.5% royalty rate set forth in the agreement and historical RITUXAN net sales. Although we are not a party to the arbitration, any damages awarded to Hoechst based on 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 and its 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.

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 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, and inequitable conduct, and seeking monetary relief in the form of costs and attorneys’ fees.

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.

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2010

Fair Value Measurements (Tables) [Abstract]

Summary of Assets and Liabilities Recorded at Fair Value


							Significant
	Balance as of		Quoted Prices in		Significant Other		Unobservable
	September 30,		Active Markets		Observable Inputs		Inputs
(In millions)	2010		(Level 1)		(Level 2)		(Level 3)

Assets:
Cash equivalents	$	534.3	$	—	$	534.3	$	—
Marketable debt securities:
Corporate debt securities		226.3		—		226.3		—
Government securities		476.0		—		476.0		—
Mortgage and other asset backed securities		55.5		—		55.5		—
Strategic investments		36.4		36.4		—		—
Venture capital investments		21.8		—		—		21.8
Derivative contracts		1.0		—		1.0		—
Plan assets for deferred compensation		12.3		—		12.3		—

Total	$	1,363.6	$	36.4	$	1,305.4	$	21.8

Liabilities:
Derivative contracts	$	24.5	$	—	$	24.5	$	—

Total	$	24.5	$	—	$	24.5	$	—


							Significant
	Balance as of		Quoted Prices in		Significant Other		Unobservable
	December 31,		Active Markets		Observable 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


	For the Three Months				For the Nine Months
	Ended September 30,				Ended September 30,
(In millions)	2010		2009		2010			2009

Beginning balance	$	20.4	$	21.6	$	21.9		$	23.9
Total net unrealized gains (losses) included in earnings		0.5		0.9		(1.1	)		(2.2	)
Net purchases, issuances, and settlements		0.9		0.6		1.0			1.4

Ending balance	$	21.8	$	23.1	$	21.8		$	23.1

Summary of fair and carrying value of debt instruments


	As of September 30, 2010				As of December 31, 2009
	Fair		Carrying		Fair		Carrying
(In millions)	Value		Value		Value		Value

Credit line from Dompé	$	10.3	$	10.2	$	17.2	$	17.2
Notes payable to Fumedica		23.6		20.9		31.3		30.0
6.0% Senior Notes due 2013		493.6		449.7		475.7		449.6
6.875% Senior Notes due 2018		646.8		599.3		589.1		603.2

Total	$	1,174.3	$	1,080.1	$	1,113.3	$	1,100.0

Collaborations (Tables)	9 Months Ended
Collaborations (Tables)	Sep. 30, 2010
Collaborations (Tables) [Abstract]
Co-promotion profit sharing formula	<!--DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" --> <!-- Begin Block Tagged Note Table: biib-20100930_note17_table1 - biib:CoPromotionProfitSharingFormulaTextBlock--> <div align="left" style="font-size: 1pt; font-family: 'Times New Roman', Times"> <table border="0" width="100%" align="center" cellpadding="0" cellspacing="0" style="font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent; text-align: left"> <!-- Table Width Row BEGIN --> <tr style="font-size: 1pt" valign="bottom"> <td width="51%"> </td><!-- colindex=01 type=maindata --> <td width="2%"> </td><!-- colindex=02 type=gutter --> <td width="1%" align="right"> </td><!-- colindex=02 type=lead --> <td width="9%" align="right"> </td><!-- colindex=02 type=body --> <td width="1%" align="left"> </td><!-- colindex=02 type=hang1 --> <td width="3%"> </td><!-- colindex=03 type=gutter --> <td width="1%" align="right"> </td><!-- colindex=03 type=lead --> <td width="15%" align="right"> </td><!-- colindex=03 type=body --> <td width="1%" align="left"> </td><!-- colindex=03 type=hang1 --> <td width="3%"> </td><!-- colindex=04 type=gutter --> <td width="1%" align="right"> </td><!-- colindex=04 type=lead --> <td width="11%" align="right"> </td><!-- colindex=04 type=body --> <td width="1%" align="left"> </td><!-- colindex=04 type=hang1 --> </tr> <!-- Table Width Row END --> <!-- TableOutputHead --> <tr style="font-size: 8pt" valign="bottom" align="center"> <td nowrap="nowrap" align="center" valign="bottom"> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom"> </td> <td> </td> <td> </td> <td colspan="6" align="center" valign="bottom" style="border-bottom: 1px solid #000000"> <b>Before First New Product FDA Approval</b> </td> <td> </td> </tr> <tr style="font-size: 8pt" valign="bottom" align="center"> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom"> <b>After First New<br /> </b> </td> <td> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom"> <b>First Non-CLL GA101<br /> </b> </td> <td> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom"> <b>GA101 CLL Sales<br /> </b> </td> <td> </td> </tr> <tr style="font-size: 8pt" valign="bottom" align="center"> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom"> <b>Product FDA<br /> </b> </td> <td> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom"> <b>FDA Approval Occurs<br /> </b> </td> <td> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom"> <b>Trigger Occurs<br /> </b> </td> <td> </td> </tr> <tr style="font-size: 8pt" valign="bottom" align="center"> <td nowrap="nowrap" align="left" valign="bottom" style="border-bottom: 1px solid #000000"> <b>Co-promotion Operating Profits†</b> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom" style="border-bottom: 1px solid #000000"> <b>Approval</b> </td> <td> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom" style="border-bottom: 1px solid #000000"> <b>First</b> </td> <td> </td> <td> </td> <td colspan="2" nowrap="nowrap" align="center" valign="bottom" style="border-bottom: 1px solid #000000"> <b>First</b> </td> <td> </td> </tr> <tr style="line-height: 3pt; font-size: 1pt"> <td> </td> </tr> <!-- TableOutputBody --> <tr valign="bottom" style="background: #cceeff"> <td nowrap="nowrap" align="left" valign="bottom"> <div style="text-indent: -10pt; margin-left: 10pt"> I. First $50.0 million </div> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 30 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 30 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 30 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> </tr> <tr valign="bottom"> <td align="left" valign="bottom"> <div style="text-indent: -10pt; margin-left: 10pt"> II. Above $50.0 million </div> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 35 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> </tr> <tr valign="bottom" style="background: #cceeff"> <td align="left" valign="bottom"> <div style="text-indent: -10pt; margin-left: 20pt"> A. Until First GA101 Threshold Date </div> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 38 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 39 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> </tr> <tr valign="bottom"> <td align="left" valign="bottom"> <div style="text-indent: -10pt; margin-left: 20pt"> B. After First GA101 Threshold Date </div> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> </tr> <tr valign="bottom" style="background: #cceeff"> <td align="left" valign="bottom"> <div style="text-indent: -10pt; margin-left: 32pt"> 1(a). Until First Threshold Date </div> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 37.5 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> </tr> <tr valign="bottom"> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> </tr> <tr valign="bottom" style="background: #cceeff"> <td align="left" valign="bottom"> <div style="text-indent: -20pt; margin-left: 42pt"> 1(b). After First Threshold Date and until Second Threshold Date </div> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 35 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> </tr> <tr valign="bottom"> <td align="left" valign="bottom"> <div style="text-indent: -10pt; margin-left: 32pt"> 1(c). After Second Threshold Date </div> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 30 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> </tr> <tr valign="bottom" style="background: #cceeff"> <td align="left" valign="bottom"> <div style="text-indent: -10pt; margin-left: 32pt"> 2. Until Second GA101 Threshold Date </div> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 37.5 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> </tr> <tr valign="bottom"> <td align="left" valign="bottom"> <div style="text-indent: -10pt; margin-left: 20pt"> C. After Second GA101 Threshold Date </div> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> 35 </td> <td nowrap="nowrap" align="left" valign="bottom"> % </td> <td> </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> <td nowrap="nowrap" align="right" valign="bottom"> — </td> <td nowrap="nowrap" align="left" valign="bottom"> </td> </tr> </table> <div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 0%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent"> </div> <div style="margin-top: 6pt; font-size: 1pt"> </div> <div style="font-size: 1pt; margin-left: 0%; width: 13%; align: left; border-bottom: 1pt solid #000000"> </div> <div style="margin-top: 3pt; font-size: 1pt"> </div> <table width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent; text-align: left"> <tr> <td width="2%"></td> <td width="1%"></td> <td width="97%"></td> </tr> <tr> <td align="right" valign="top"> <font style="font-size: 9pt">† </font></td> <td></td> <td valign="bottom"> <u><font style="font-size: 9pt">First GA101 Threshold Date</font></u><font style="font-size: 9pt"> 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 reach $150.0 million or (2) the first day of the calendar quarter following the date following 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. </font></td> </tr> <tr style="line-height: 3pt; font-size: 1pt"> <td> </td> </tr> <tr> <td align="right" valign="top"> <font style="font-size: 9pt"> </font></td> <td></td> <td valign="bottom"> <u><font style="font-size: 9pt">Second GA101 Threshold Date</font></u><font style="font-size: 9pt"> 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. </font></td> </tr> <tr style="line-height: 3pt; font-size: 1pt"> <td> </td> </tr> <tr> <td align="right" valign="top"> <font style="font-size: 9pt"> </font></td> <td></td> <td valign="bottom"> <u><font style="font-size: 9pt">First Threshold Date</font></u><font style="font-size: 9pt"> 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. </font></td> </tr> <tr style="line-height: 3pt; font-size: 1pt"> <td> </td> </tr> <tr> <td align="right" valign="top"> <font style="font-size: 9pt"> </font></td> <td></td> <td valign="bottom"> <u><font style="font-size: 9pt">Second Threshold Date</font></u><font style="font-size: 9pt"> 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. </font></td> </tr> </table> </div>

Revenue Recognition (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Revenue Recognition (Details) - USD ($) $ in Millions	Mar. 31, 2010	Mar. 31, 2009	Sep. 30, 2010	Sep. 30, 2010	Dec. 31, 2009
Analysis of the amount of, and change in, product revenue reserves [Abstract]
Balance, as of December 31, 2009	$ 103.1		$ 103.1
Current provisions relating to sales in current year			275.0
Adjustments relating to prior years			(6.4)
Payments/returns relating to sales in current year			(156.7)
Payments/returns relating to sales in prior years			(79.7)
Balance, as of September 30, 2010			135.3
Summary of total product revenue reserves included in consolidated balance sheets [Abstract]
Reduction of accounts receivable				$ 34.7	$ 43.3
Current liability				100.6	59.8
Total reserves	$ 103.1		103.1	135.3	103.1
Revenue Recognition (Textuals) [Abstract]
Deferred Revenue		$ 125.0
New minimum Medicaid rate after implementation of new Healthcare Reform	23.10%
Old minimum Medicaid rate before implementation of new Healthcare Reform	15.10%
Discount percentage to Medicare beneficiaries whose prescription drug costs become subject to Medicare Part D coverage gap	50.00%
Expected aggregate Industry fees			28,000.0
Maximum industry fees annual			2,500.0
Accounts receivable in countries with deteriorated credit and economic conditions				250.4
Discounts [Member]
Analysis of the amount of, and change in, product revenue reserves [Abstract]
Balance, as of December 31, 2009	$ 13.9		13.9
Current provisions relating to sales in current year			58.0
Adjustments relating to prior years			(2.4)
Payments/returns relating to sales in current year			(45.9)
Payments/returns relating to sales in prior years			(9.5)
Balance, as of September 30, 2010			14.1
Summary of total product revenue reserves included in consolidated balance sheets [Abstract]
Total reserves	13.9		13.9	14.1	13.9
Contractual Adjustments [Member]
Analysis of the amount of, and change in, product revenue reserves [Abstract]
Balance, as of December 31, 2009	70.3		70.3
Current provisions relating to sales in current year			204.7
Adjustments relating to prior years			(2.2)
Payments/returns relating to sales in current year			(110.3)
Payments/returns relating to sales in prior years			(60.7)
Balance, as of September 30, 2010			101.8
Summary of total product revenue reserves included in consolidated balance sheets [Abstract]
Total reserves	70.3		70.3	101.8	70.3
Returns [Member]
Analysis of the amount of, and change in, product revenue reserves [Abstract]
Balance, as of December 31, 2009	18.9		18.9
Current provisions relating to sales in current year			12.3
Adjustments relating to prior years			(1.8)
Payments/returns relating to sales in current year			(0.5)
Payments/returns relating to sales in prior years			(9.5)
Balance, as of September 30, 2010			19.4
Summary of total product revenue reserves included in consolidated balance sheets [Abstract]
Total reserves	$ 18.9		$ 18.9	$ 19.4	$ 18.9

Intangible Assets and Goodwill (Details) $ in Thousands	3 Months Ended		9 Months Ended
Intangible Assets and Goodwill (Details) $ in Thousands	Sep. 30, 2010 USD ($)	Sep. 30, 2009 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2009 USD ($)	Dec. 31, 2009 USD ($)
Intangible assets
Estimated Life			Indefinite
Cost of trademarks and tradenames	$ 64,000		$ 64,000		$ 64,000
Accumulated amortization of trademarks and tradenames	0		0		0
Trademarks and tradenames, net	64,000		64,000		64,000
Net	1,715,342		1,715,342		1,871,078
Intangible Assets and Goodwill (Textuals) [Abstract]
Net Book Value Avonex Core Technology Intangible Asset	1,396,700		1,396,700
Amortization of acquired intangible assets	53,500	$ 51,300	155,600	$ 233,800
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
Out-licensed patents [Member]
Intangible assets
Estimated Life (In Years)			12
Cost	578,000		$ 578,000		578,000
Accumulated Amortization	(339,900)		(339,900)		(306,000)
Net	238,100		$ 238,100		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		3,005,300
Accumulated Amortization	(1,593,900)		(1,593,900)		(1,472,400)
Net	1,411,400		$ 1,411,400		1,532,900
In-licensed patents [Member]
Intangible assets
Estimated Life (In Years)			14
Cost	3,000		$ 3,000		3,000
Accumulated Amortization	(1,300)		(1,300)		(1,100)
Net	1,700		$ 1,700		1,900
Assembled workforce [Member]
Intangible assets
Estimated Life (In Years)			4
Cost	2,100		$ 2,100		2,100
Accumulated Amortization	(2,000)		(2,000)		(1,800)
Net	100		$ 100		300
Distribution rights [Member]
Intangible assets
Estimated Life (In Years)			2
Cost	12,700		$ 12,700		12,700
Accumulated Amortization	(12,700)		(12,700)		(12,700)
Net	0		0		0
Total intangible assets [Member]
Intangible assets
Cost	3,665,100		3,665,100		3,665,100
Accumulated Amortization	(1,949,800)		(1,949,800)		(1,794,000)
Net	$ 1,715,300		$ 1,715,300		$ 1,871,100

Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
Fair Value Measurements (Details) - USD ($) $ in Millions	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2010	Sep. 30, 2009	Dec. 31, 2009
Assets:
Cash equivalents	$ 534.3		$ 534.3		$ 476.4
Derivative contracts	1.0		1.0		15.8
Plan assets for deferred compensation	12.3		12.3		13.6
Total	1,363.6		1,363.6		2,409.5
Liabilities:
Derivative contracts	24.5		24.5		11.1
Total	24.5		24.5		$ 11.1
Fair value of venture capital investments
Beginning balance	20.4	$ 21.6	21.9	$ 23.9
Total net unrealized gains (losses) included in earnings	0.5	0.9	(1.1)	(2.2)
Net purchases, issuances and settlements	0.9	0.6	1.0	1.4
Ending balance	$ 21.8	$ 23.1	$ 21.8	$ 23.1
Fair Value Measurements (Textuals) [Abstract]
Percentage of Venture capital investments to total assets	0.30%		0.30%		0.30%
Quoted Prices in Active Markets, Level 1 [Member]
Liabilities:
Derivative contracts	$ 0.0		$ 0.0		$ 0.0
Total	0.0		0.0		0.0
Fair Value, Inputs, Level 2 [Member]
Liabilities:
Derivative contracts	24.5		24.5		11.1
Total	24.5		24.5		11.1
Fair Value, Inputs, Level 3 [Member]
Liabilities:
Derivative contracts	0.0		0.0		0.0
Total	0.0		0.0		0.0
Corporate Debt Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	226.3		226.3		504.1
US Treasury and Government [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	476.0		476.0		1,133.5
Asset-backed Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	55.5		55.5		238.3
Strategic investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	36.4		36.4		5.9
Venture capital investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	21.8		21.8		21.9
Quoted Prices in Active Markets, Level 1 [Member]
Assets:
Cash equivalents	0.0		0.0		0.0
Derivative contracts	0.0		0.0		0.0
Plan assets for deferred compensation	0.0		0.0		0.0
Total	36.4		36.4		5.9
Quoted Prices in Active Markets, Level 1 [Member] \| Corporate Debt Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0		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		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		0.0
Quoted Prices in Active Markets, Level 1 [Member] \| Strategic investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	36.4		36.4		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		0.0
Fair Value, Inputs, Level 2 [Member]
Assets:
Cash equivalents	534.3		534.3		476.4
Derivative contracts	1.0		1.0		15.8
Plan assets for deferred compensation	12.3		12.3		13.6
Total	1,305.5		1,305.5		2,381.7
Fair Value, Inputs, Level 2 [Member] \| Corporate Debt Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	226.3		226.3		504.1
Fair Value, Inputs, Level 2 [Member] \| US Treasury and Government [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	476.0		476.0		1,133.5
Fair Value, Inputs, Level 2 [Member] \| Asset-backed Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	55.5		55.5		238.3
Fair Value, Inputs, Level 2 [Member] \| Strategic investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0		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		0.0
Fair Value, Inputs, Level 3 [Member]
Assets:
Cash equivalents	0.0		0.0		0.0
Derivative contracts	0.0		0.0		0.0
Plan assets for deferred compensation	0.0		0.0		0.0
Total	21.8		21.8		21.9
Fair Value, Inputs, Level 3 [Member] \| Corporate Debt Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0		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		0.0
Fair Value, Inputs, Level 3 [Member] \| Asset-backed Securities [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	0.0		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		0.0
Fair Value, Inputs, Level 3 [Member] \| Venture capital investments [Member]
Assets:
Fair Value, Measured on Recurring Basis, Investments	21.8		21.8		21.9
Fair Value [Member]
Summary of fair and carrying value of debt instruments
Fair Value Total	1,174.3		1,174.3		1,113.3
Fair Value [Member] \| Dompe [Member]
Summary of fair and carrying value of debt instruments
Credit line from Dompe, Fair Value	10.3		10.3		17.2
Fair Value [Member] \| Notes payable Fumedica [Member]
Summary of fair and carrying value of debt instruments
Notes Payable, Fair Value	23.6		23.6		31.3
Fair Value [Member] \| 6.0% Senior Notes [Member]
Summary of fair and carrying value of debt instruments
Notes Payable, Fair Value	493.6		493.6		475.7
Fair Value [Member] \| 6.875% Senior Notes [Member]
Summary of fair and carrying value of debt instruments
Notes Payable, Fair Value	646.8		646.8		589.1
Carrying Value [Member]
Summary of fair and carrying value of debt instruments
Carrying Value Total	1,080.1		1,080.1		1,100.0
Carrying Value [Member] \| Dompe [Member]
Summary of fair and carrying value of debt instruments
Credit line from Dompe, Carrying Value	10.2		10.2		17.2
Carrying Value [Member] \| Notes payable Fumedica [Member]
Summary of fair and carrying value of debt instruments
Notes Payable, Carrying Value	20.9		20.9		30.0
Carrying Value [Member] \| 6.0% Senior Notes [Member]
Summary of fair and carrying value of debt instruments
Notes Payable, Carrying Value	449.7		449.7		449.6
Carrying Value [Member] \| 6.875% Senior Notes [Member]
Summary of fair and carrying value of debt instruments
Notes Payable, Carrying Value	$ 599.3		$ 599.3		$ 603.2

Financial Instruments (Details) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
Financial Instruments (Details) $ in Thousands	Sep. 30, 2010 USD ($)	Sep. 30, 2009 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2009 USD ($)	Dec. 31, 2009 USD ($)
Marketable Securities including Strategic Investments
Fair Value	$ 757,800		$ 757,800		$ 1,875,900
Gross Unrealized Gains			5,300		16,700
Gross Unrealized Losses			(400)		(1,300)
Amortized Cost	752,900		752,900		1,860,500
Summary of Contractual Maturities: Available-for-Sale Securities
Due in one year or less, Estimated Fair Value	168,200		168,200		522,000
Due in one year or less, Amortized Cost	167,900		167,900		519,500
Due after one year through five years, Estimated Fair Value	545,900		545,900		1,143,700
Due after one year through five years, Amortized Cost	541,600		541,600		1,133,400
Due after five years, Estimated Fair Value	43,700		43,700		210,200
Due after five years, Amortized Cost	43,400		43,400		207,600
Total Fair Value	757,800		757,800		1,875,900
Total Amortized Cost	752,900		752,900		1,860,500
Proceeds from Marketable Securities, excluding Strategic Investments
Proceeds from maturities and sales	487,800	$ 696,500	2,490,363	$ 2,334,093
Realized gains	5,000	3,100	18,100	17,000
Realized losses	200	1,300	$ 2,000	3,400
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	127,200		$ 127,200		298,800
Fair and carrying values of commercial paper including accrued interest	148,500		148,500		76,900
Fair and carrying values of short-term debt securities	385,800		385,800		$ 399,500
Other-than-temporary impairment of available-for-sale securities primarily related to mortgage and asset backed securities, when lacking the ability and intent to hold the securities to recovery	$ 2,800	$ 500	19,800	$ 6,500
Other-than-temporary impairment of available-for-sale securities primarily related to marketable debt securities			$ 3,600
Average maturity of marketable securities, months	13		13		15
Corporate debt securities Current [Member]
Marketable Securities including Strategic Investments
Fair Value	$ 55,300		$ 55,300		$ 177,200
Gross Unrealized Gains			100		1,500
Gross Unrealized Losses			0
Amortized Cost	55,200		55,200		175,700
Corporate Debt Securities Non-Current [Member]
Marketable Securities including Strategic Investments
Fair Value	171,000		171,000		326,900
Gross Unrealized Gains			3,300		5,700
Gross Unrealized Losses			(100)		(300)
Amortized Cost	167,800		167,800		321,500
Government securities Current [Member]
Marketable Securities including Strategic Investments
Fair Value	142,400		142,400		501,600
Gross Unrealized Gains			200		1,200
Gross Unrealized Losses			0
Amortized Cost	142,200		142,200		500,400
Government Securities Non-Current [Member]
Marketable Securities including Strategic Investments
Fair Value	333,600		333,600		631,900
Gross Unrealized Gains			1,300		4,100
Gross Unrealized Losses			(100)		(500)
Amortized Cost	332,400		332,400		628,300
Mortgage and other asset backed securities Current [Member]
Marketable Securities including Strategic Investments
Fair Value	100		100		3,000
Gross Unrealized Gains			0		100
Gross Unrealized Losses			0
Amortized Cost	100		100		2,900
Mortgage And Other Asset Backed Securities Non Current [Member]
Marketable Securities including Strategic Investments
Fair Value	55,400		55,400		235,300
Gross Unrealized Gains			400		4,100
Gross Unrealized Losses			(200)		(500)
Amortized Cost	55,200		55,200		231,700
Other Strategic investments Non-Current [Member]
Marketable Securities including Strategic Investments
Gross Unrealized Gains			7,200		2,700
Gross Unrealized Losses			0		(300)
Amortized Cost	29,200		29,200		3,500
Strategic investments, non-current Fair Value	$ 36,400		$ 36,400		$ 5,900

Derivative Instruments (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
Derivative Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2010	Sep. 30, 2009	Jun. 30, 2009	Sep. 30, 2010	Sep. 30, 2009	Dec. 31, 2009
Foreign currency forward contracts that were entered into to hedge forecasted revenue
Notional Amount of Foreign Currency Cash Flow Hedge Derivatives	$ 541.2			$ 541.2		$ 518.2
Derivative Instruments (Textuals) [Abstract]
Lower Range of Durations of foreign currency forward contracts	1			1		1
Higher Range of Durations of foreign currency forward contracts	13			13		13
Gain/Loss on fair value of Foreign currency forward contracts	$ 17.1			$ 17.1		$ 1.2
Derivative, Net Hedge Ineffectiveness Gain (Loss)	1.4	$ 0.1		0.9	$ 0.9
Gains/(Losses) in product revenue for the settlement of certain effective cash flow hedge instruments	20.7	16.3		40.6	28.6
Aggregate notional amount of outstanding foreign currency contracts	170.1			170.1
Fair Value of outstanding foreign currency contracts	7.0			7.0
Net losses of other income (expense) related to foreign currency forward contracts	10.1		$ 2.2	3.0	2.2
Other Current Assets [Member]
Summary of Derivatives designated as Hedging Instruments
Derivative Asset Designated as Hedging Instrument, Fair Value	0.0			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	16.5			16.5		9.8
Foreign Exchange Contract [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 )	(17.1)	(34.7)		(17.1)	(34.7)
Foreign Exchange Contract [Member] \| Revenue [Member]
Summary of the effect of derivatives designated as hedging instruments on the consolidated statements of income
Amount Reclassified from Accumulated Other Comprehensive Income into Income Gain/(Loss) (Effective Portion )	20.7	(16.3)		40.6	(28.6)
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 )	1.4	$ (0.1)		0.9	$ (0.9)
Euro Member Countries, Euro
Foreign currency forward contracts that were entered into to hedge forecasted revenue
Notional Amount of Foreign Currency Cash Flow Hedge Derivatives	511.6			511.6		495.9
Canada, Dollars
Foreign currency forward contracts that were entered into to hedge forecasted revenue
Notional Amount of Foreign Currency Cash Flow Hedge Derivatives	$ 29.6			$ 29.6		$ 22.3

Property, Plant and Equipment (Details) $ in Thousands	1 Months Ended	9 Months Ended
Property, Plant and Equipment (Details) $ in Thousands	Oct. 31, 2010 USD ($)	Sep. 30, 2010 USD ($)	Dec. 31, 2009 USD ($)
Net carrying amounts of assets
Property, plant and equipment, net		$ 1,641,791	$ 1,637,083
Accumulated depreciation of property, plant and equipment (Textuals) [Abstract]
Accumulated depreciation		737,700	$ 642,500
San Diego Facility [Member]
Net carrying amounts of assets
Property, plant and equipment, net		$ 128,400
Accumulated depreciation of property, plant and equipment (Textuals) [Abstract]
Sales agreement of San Diego facility	$ 128,000
Acres of Land		43
Square feet of Laboratory and Office Space		355,000
Square footage to be leased, if exercise option to lease build to suit property		160,000
Sale - Leaseback transaction period in months		15
Lease term associated with option to lease build to suit property		10
Total Debt service and interest payments, Sale Leaseback Transaction		$ 9,400
Amount held in escrow by buyer, to be received in exchange for exercising option to lease build to suit property		22,000
Land [Member] \| San Diego Facility [Member]
Net carrying amounts of assets
Property, plant and equipment, net		46,100
Buildings [Member] \| San Diego Facility [Member]
Net carrying amounts of assets
Property, plant and equipment, net		73,800
Machinery and Equipment [Member] \| San Diego Facility [Member]
Net carrying amounts of assets
Property, plant and equipment, net		5,800
Furniture and Fixtures [Member] \| San Diego Facility [Member]
Net carrying amounts of assets
Property, plant and equipment, net		$ 2,700

Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
Comprehensive Income (Details) - USD ($) $ in Thousands	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2010	Sep. 30, 2009
Comprehensive income:
Net income	$ 112,179	$ 279,602	$ 626,821	$ 671,066
Unrealized gains (losses) on investments	5,800	(500)	(3,600)	3,000
Unrealized gains (losses) on foreign currency forward contract	(71,100)	(2,300)	(16,800)	9,600
(Over) underfunded status of pension and post-retirement benefits plans	200	200	(100)	200
Translation adjustments	88,900	29,700	(40,500)	37,300
Comprehensive income (loss)	136,000	306,700	565,800	721,200
Stockholders' Equity attributable to Noncontrolling interest- rollforward
Noncontrolling interest, beginning of period	40,500	33,200	40,352	27,900
Fair Value of assets and liabilities acquired and assigned to noncontrolling interests	145,000		145,000
Net income attributable to noncontrolling interest	(141,936)	1,939	(138,174)	6,571
Translation adjustments	4,500	1,300	(1,300)	1,900
Distributions to noncontrolling interest	(8,900)	(2,800)	(8,900)	(2,800)
Capital contributions from noncontrolling interest	300		2,500
Noncontrolling interest, end of period	39,506	33,600	39,506	33,600
Comprehensive Income (Textuals) [Abstract]
Tax on unrealized holding gains (losses) on investments	3,400	300	2,100	1,700
Tax on unrealized gains (losses) on foreign currency forward contracts	8,000	800	1,500	300
Parent [Member]
Comprehensive income:
Net income	254,100	277,700	765,000	664,500
Unrealized gains (losses) on investments	5,800	(500)	(3,600)	3,000
Unrealized gains (losses) on foreign currency forward contract	(71,100)	(2,300)	(16,800)	9,600
(Over) underfunded status of pension and post-retirement benefits plans	200	200	(100)	200
Translation adjustments	84,400	28,400	(39,200)	35,400
Comprehensive income (loss)	273,400	303,500	705,300	712,700
Noncontrolling Interest [Member]
Comprehensive income:
Net income	(141,900)	1,900	(138,200)	6,600
Translation adjustments	4,500	1,300	(1,300)	1,900
Comprehensive income (loss)	$ (137,400)	$ 3,200	$ (139,500)	$ 8,500

Earnings per Share (Details) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2010	Sep. 30, 2009
Numerator:
Net income attributable to Biogen Idec	$ 254,115	$ 277,663	$ 764,995	$ 664,495
Adjustment for net income allocable to preferred share	(500)	(500)	(1,500)	(1,100)
Net income used in calculating basic and diluted earnings per share	$ 253,600	$ 277,200	$ 763,500	$ 663,400
Denominator:
Weighted average number of common shares outstanding	239,864	288,917	256,586	288,416
Effect of dilutive securities:
Stock options and employee stock purchase plan	900	600	900	700
Time-vested restricted stock units	1,500	1,500	1,400	1,300
Market stock units	0	0	0	0
Performance-vested restricted stock units settled in shares	0	0	0	0
Dilutive potential common shares	2,400	2,100	2,300	2,000
Shares used in calculating diluted earnings per share	242,313	291,037	258,906	290,368
Numerator:
Net income allocable to preferred shares	$ 500	$ 500	$ 1,500	$ 1,100
Denominator:
Stock options	4,500	8,400	4,900	7,400
Time-vested restricted stock units	1,200	2,300	1,000	2,100
Market stock units
Performance-vested restricted stock units settled in shares		200		100
Convertible preferred stock	500	500	500	500
Total	6,200	11,400	6,400	10,100

Share-Based Payments (Details)	3 Months Ended		9 Months Ended
Share-Based Payments (Details)	Sep. 30, 2010 USD ($) shares	Sep. 30, 2009 USD ($) shares	Sep. 30, 2010 USD ($) shares	Sep. 30, 2009 USD ($) shares
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	$ 41,900,000	$ 41,100,000	$ 142,600,000	$ 119,900,000
Capitalized share-based payment costs	(900,000)	(1,700,000)	(2,500,000)	(4,800,000)
Income tax effect	(13,000,000)	(12,600,000)	(45,400,000)	(36,800,000)
Summary of share based compensation expense associated with different programs
Stock options	$ 3,000,000	5,500,000	$ 23,100,000	16,600,000
Market stock units \| shares	2,300,000		7,800,000
Time-vested restricted stock units	$ 30,800,000	$ 34,400,000	$ 96,500,000	$ 99,900,000
Performance-vested restricted stock units settled in shares \| shares	700,000	(300,000)	4,400,000	3,000,000
Performance-vested restricted stock units settled in cash	$ 2,700,000		$ 8,000,000
Employee stock purchase plan	3,300,000	$ 3,200,000	5,300,000	$ 5,200,000
Capitalized share-based payment costs	(900,000)	(1,700,000)	(2,500,000)	(4,800,000)
Share-based compensation expense included in total costs and expenses	41,900,000	41,100,000	$ 142,600,000	$ 119,900,000
Share Based Payments (Textuals) [Abstract]
Employee stock purchase plan \| shares			457,000	426,000
Percentage of granted PVRSUs earned on the basis of 2009 performance			99.00%
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, maximum			$ 54.12
60 calendar day average stock price on grant date, Minimum			$ 49.08
Number of new forms of equity-based compensation			2
Number of equal annual increments for Market Stock Units awards			4
Calendar day average closing stock price on grant date for Market Stock Units			60
Restricted stock units received by executive \| shares			63,165
Market stock units received by executive \| shares			56,905
Number of equal annual increments for Cash Settled Performance Shares awards			3
Calendar day average closing stock price for Cash Settled Performance Shares based on vesting date			60
Minimum target number of market stock units granted based on stock performance in percent			0.00%
Maximum target number of market stock units granted based on stock performance in percent			150.00%
Minimum Earning of target number of units granted based on the degree of actual performance metric achievement			0.00%
Maximum Earning of target number of units granted based on the degree of actual performance metric achievement			200.00%
Purchase price of common stock under the employee stock purchase plan			85.00%
Discount of the purchase price of common stock under the employee stock purchase plan			15.00%
Percentage of granted PVRSUs earned on the basis of 2009 performance			99.00%
Lower Range [Member]
Assumptions used in Valuation of Market Based Stock Units
Range of expected stock price volatility			28.30%
Higher Range [Member]
Assumptions used in Valuation of Market Based Stock Units
Range of expected stock price volatility			38.80%
Stock Options [Member]
Share Based Payments (Textuals) [Abstract]
Number Granted \| shares			124,000	1,000,000
Weighted Average Grant Date Fair Value			$ 16.52	$ 18.01
Weighted Average Exercise Price			$ 57.38	$ 50.02
Time vested Restricted stock units [Member]
Share Based Payments (Textuals) [Abstract]
Number Granted \| shares			2,000,000	2,500,000
Weighted Average Grant Date Fair Value			$ 54.63	$ 49.35
Performance vested Restricted stock units [Member]
Share Based Payments (Textuals) [Abstract]
Number Granted \| shares				321,000
Weighted Average Grant Date Fair Value				$ 49.46
Market stock units [Member]
Share Based Payments (Textuals) [Abstract]
Number Granted \| shares			400,000
Weighted Average Grant Date Fair Value			$ 61.87
Cash settled performance shares [Member]
Share Based Payments (Textuals) [Abstract]
Number Granted \| shares			378,000
Research and development [Member]
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	15,900,000	15,600,000	$ 48,000,000	46,000,000
Summary of share based compensation expense associated with different programs
Share-based compensation expense included in total costs and expenses	15,900,000	15,600,000	48,000,000	46,000,000
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	26,900,000	27,200,000	97,100,000	78,700,000
Summary of share based compensation expense associated with different programs
Share-based compensation expense included in total costs and expenses	26,900,000	27,200,000	97,100,000	78,700,000
Subtotal [Member]
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	42,800,000	42,800,000	145,100,000	124,700,000
Summary of share based compensation expense associated with different programs
Share-based compensation expense included in total costs and expenses	42,800,000	42,800,000	145,100,000	124,700,000
Parent [Member]
Share-based Compensation Expense included in consolidated statements of income
Share-based compensation expense included in total costs and expenses	28,900,000	28,500,000	97,200,000	83,100,000
Summary of share based compensation expense associated with different programs
Share-based compensation expense included in total costs and expenses	$ 28,900,000	$ 28,500,000	$ 97,200,000	$ 83,100,000

Income Taxes (Details) $ in Millions	3 Months Ended			9 Months Ended
Income Taxes (Details) $ in Millions	Sep. 30, 2010 USD ($)	Sep. 30, 2009	Jun. 30, 2009 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2009	Jun. 08, 2010 USD ($)	Sep. 12, 2006 USD ($)
Reconciliation between the U.S. federal statutory tax rate and effective tax rate
Statutory rate	35.00%	35.00%		35.00%	35.00%
State taxes	2.40%	2.20%		2.00%	1.60%
Taxes on foreign earnings	(13.60%)	(7.70%)		(10.80%)	(5.80%)
Credits and net operating loss utilization	(4.30%)	(1.50%)		(2.20%)	(4.10%)
Purchased intangible assets	2.90%	0.90%		1.80%	2.00%
IPR&D	21.60%	0.90%		5.20%	1.10%
Permanent items	(3.80%)	(1.00%)		(2.10%)	(1.50%)
Other	(0.10%)	0.20%		(0.20%)	0.50%
Effective tax rate	40.10%	29.00%		28.70%	28.80%
Income Taxes (Textuals) [Abstract]
Effective tax rate	40.10%	29.00%		28.70%	28.80%
Notice of Assessment of corporate excise tax including penalties and interest						$ 103.5	$ 38.9
Total assessment, including interest and penalties, under dispute	$ 142.4			$ 142.4
Increase in effective tax rate due to collaboration		2.40%			2.30%
Impact of changes in tax law on effective tax rate					3.20%
Upfront payment incurred in connection with collaboration license agreement with Acorda Therapeutics, Inc. Acorda			$ 110.0
Knopp [Member]
Income Taxes [Line Items]
IPR&D charge allocated to noncontrolling interest	$ 145.0			$ 145.0
Impact On Effective Tax Rates Of Collaboration	0.135			0.027

Investments in Variable Interest Entities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2010	Sep. 30, 2009
Investment in Variable Interest Entities (Textuals) [Abstract]
IPR&D charge recorded related to collaboration agreement	$ 319,054	$ 304,055	$ 957,759	$ 999,986
Investment in biotechnology that determined to be unconsolidated variable interest entities	22,700		22,700
Receivable related to cost sharing arrangement	7,900		7,900
Total joint venture assets	167,100		167,100
Total joint venture liabilities	75,100		75,100
Account receivable from ordinary course of business related to Joint Ventures	118,500		118,500
Knopp [Member]
Summary of activity related to collaborations
Total development expense incurred by the collaboration	1,000		1,000
Biogen Idec's share of expense reflected within our consolidated statements of income	27,400		27,400
Total upfront and reimbursent payment made to collaborative partner	26,400		26,400
Investment in Variable Interest Entities (Textuals) [Abstract]
Total upfront and reimbursent payment made to collaborative partner	26,400		26,400
Remaining potential development milestone payments and royalties on commercial sales under the terms of collaboration agreement			$ 265,000
Minimum number of years of product term from the first commercial sales			10
Purchase of Class B common shares of Knopp			30.00%
Purchase consideration for Knopp			$ 60,000
IPR&D charge recorded related to collaboration agreement			$ 205,000
Discount rate to value Dexpramipexole			14.00%
IPR&D charge allocated to noncontrolling interest	145,000		$ 145,000
Neurimmune [Member]
Summary of activity related to collaborations
Milestone payments made to collaborative partner				7,500
Total development expense incurred by the collaboration	2,400	1,900	12,800	5,500
Biogen Idec's share of expense reflected within our consolidated statements of income	2,400	1,900	12,800	13,000
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%
Milestone payments to be paid in the future to collaborative partner				7,500
Cardiokine [Member]
Summary of activity related to collaborations
Milestone payments made to collaborative partner		20,000		20,000
Total development expense incurred by the collaboration	10,900	17,200	$ 47,400	48,500
Biogen Idec's share of expense reflected within our consolidated statements of income	9,800	35,500	42,700	63,700
Collaboration expense allocated to noncontrolling interests, net of tax	$ 1,100	1,700	4,700	4,800
Investment in Variable Interest Entities (Textuals) [Abstract]
Remaining potential development milestone payments and royalties on commercial sales under the terms of collaboration agreement			$ 100,000
Percentage of funding for R&D cost required in support of the collaboration agreement			90.00%
Milestone payments to be paid in the future to collaborative partner		$ 20,000		$ 20,000

Collaborations (Details) $ in Millions	9 Months Ended
Collaborations (Details) $ in Millions	Sep. 30, 2010 USD ($)
Ocrelizumab [member] \| Maximum [Member]
Collaborations (Textuals) [Abstract]
Future royalties percentage to be received on sale of ocrelizumab	24.00%
Ocrelizumab [member] \| Minimum [Member]
Collaborations (Textuals) [Abstract]
Future royalties percentage to be received on sale of ocrelizumab	13.50%
GA101 [Member]
Collaborations (Textuals) [Abstract]
Percentage of future development and commercialization expenses payable related to GA101	0.35
Sharing percentage of development expenses of GA101, prior to amendment	0.3
Compensation payment under terms of amendment for reimbursement of increased share of previously incurred expenses	$ 10.0
GA101 [Member] \| Maximum [Member]
Collaborations (Textuals) [Abstract]
Profit sharing on sale of GA101, percentage	39.00%
GA101 [Member] \| Minimum [Member]
Collaborations (Textuals) [Abstract]
Profit sharing on sale of GA101, percentage	35.00%
RITUXAN [Member]
Collaborations (Textuals) [Abstract]
Percentage of Co promotion Operating Profits first fifty million, prior to October 2010 amendment	30.00%
Copromotion operating profit threshold for RITUXAN in the US and Canada, to determine share of copromotion operating profit, prior to October 2010 amendment	$ 50.0
Percentage of share of copromotion profits exceeding $50 million, prior to October 2010 amendment	0.4
Threshold of gross sales of GA 101 to be achieved in preceding 12 consecutive months under option one	$ 150.0
Threshold of gross sales of GA 101 to be achieved in any 12 consecutive months under option one	150.0
Threshold of gross sales of GA 101 to be achieved in any 12 consecutive months under option two	500.0
Threshold of earlier of GA101 CLL trigger, the second GA101 CLL sales trigger, and gross sales of New Product to be achieved in any calender year under sub option one and two of option two	150.0
Threshold of gross sales of New Product to be achieved in same calender year under sub option one and two of option two	150.0
Threshold of gross sales of new product to be achieved in any calender year under sub option three of option two	$ 350.0
RITUXAN [Member] \| After First New Product FDA Approval [Member]
Co-promotion profit sharing formula
First $ 50.0 million	0.3
Until First GA 101 Threshold Date	0.38
After First GA 101 Threshold Date
Until First Threshold Date	0.375
After First Threshold Date and until Second Threshold Date	0.35
After Second Threshold Date	0.3
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	0.3
Until First GA 101 Threshold Date	0.39
After First GA 101 Threshold Date
Until Second GA 101 Threshold Date	0.375
After Second GA 101 Threshold Date	0.35
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	0.3
Above $50.0 million	0.35
RITUXAN [Member] \| GA101 [Member]
Collaborations (Textuals) [Abstract]
GA101 CLL Sales Trigger - US GA101 gross sales threshold	$ 500.0

Revenue Recognition (Policies)	9 Months Ended
Revenue Recognition (Policies)	Sep. 30, 2010
Revenue Recognition (Policies) [Abstract]
Adoption of ASU No. 2009-13 and its effect	During the third quarter of 2010, we elected to early adopt 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 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 as applied to all previously reported interim periods in the fiscal year of adoption. Our adoption of this standard did not have a material impact our financial position or results of operations as through the third quarter of 2010, we had not recorded any revenue in accordance with revenue recognition rules for multiple deliverables as described in ASU 2009-13 or its predecessor pronouncements.

New Accounting Pronouncements (Policies)	9 Months Ended
New Accounting Pronouncements (Policies)	Sep. 30, 2010
New Accounting Pronouncements (Policies) [Abstract]
Adoption of ASU No. 2010-17 and its effect	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, adoption of this guidance as of a date other than January 1, 2011 will require us to apply this guidance retrospectively effective as of January 1, 2010 and will require disclosure of the effect of this guidance as applied to all previously reported interim periods in the fiscal year of adoption. As we plan to implement ASU 2010-17 prospectively, 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.

Acquisitions and Dispositions (Details) $ in Millions	Sep. 30, 2010 USD ($)
Biogen Idec Hemophilia Inc. [Member]
Acquisitions and Dispositions (Textuals) [Abstract]
Payment to former shareholders of Syntonix Pharmaceuticals	$ 40.0

Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2010	Dec. 31, 2009
Components of inventories [Abstract]
Raw materials	$ 51,600	$ 49,200
Work in process	126,000	174,000
Finished goods	91,700	70,800
Total inventory	$ 269,313	$ 293,950

Other Income (Expense), Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2010	Sep. 30, 2009	Sep. 30, 2010	Sep. 30, 2009
Other income (expense), net
Interest income	$ 3,100	$ 10,900	$ 18,600	$ 37,800
Interest expense	(9,300)	(8,500)	(26,600)	(27,600)
Impairments of investments	(2,800)	(500)	(19,800)	(10,100)
Net gains (losses) on foreign currency transactions	(3,500)	3,200	(3,200)	10,600
Net realized gains (losses) on marketable securities	4,800	1,800	16,100	13,700
Other, Net	800	2,500	600	6,500
Total other income (expense), net	$ (6,945)	$ 9,360	$ (14,318)	$ 30,886

Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($)	Sep. 30, 2010	Dec. 31, 2009
Shareholders' equity:
Preferred stock, par value	$ 0.001	$ 0.001
Common stock, par value	$ 0.0005	$ 0.0005

Overview (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended
Overview (Details) - USD ($) $ in Millions	Oct. 31, 2010	Sep. 30, 2010
Overview (Textuals) [Abstract]
Interest in subsidiary (less than given percentage)		100.00%
San Diego Facility [Member]
Subsequent Event [Line Items]
Sales agreement of San Diego facility	$ 128.0
Sale - Leaseback transaction period in months		15

Litigation (Details) - USD ($) $ in Millions	1 Months Ended	9 Months Ended	12 Months Ended
Litigation (Details) - USD ($) $ in Millions	Jun. 30, 2010	Sep. 30, 2010	Dec. 31, 2006
Litigation (Textuals) [Abstract]
Notice of assessment under consideration for corporate excise tax	$ 103.5		$ 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%