Consolidated Statements of Equity (USD $) In Thousands, except Share data	Total	Total Biogen Idec Inc. shareholders' equity	Preferred stock	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Retained earnings	Treasury stock	Noncontrolling interests
Beginning Balance at Dec. 31, 2010	$ 5,449,443	$ 5,396,506	$ 0	$ 124	$ 3,895,103	$ (21,610)	$ 1,872,481	$ (349,592)	$ 52,937
Beginning Balance, shares at Dec. 31, 2010			8,000	248,200,000				(7,662,000)
Net income	1,266,686	1,234,428					1,234,428		32,258
Other comprehensive income, net of tax	(22)	(4,925)				(4,925)			4,903
Distributions to noncontrolling interests	(27,062)	(148)					(148)		(26,914)
Repurchase of common stock for Treasury pursuant to the 2011 share repurchase plan, at cost	(497,975)	(497,975)						(497,975)
Repurchase of common stock for Treasury pursuant to the 2011 stock repurchase plan, at cost, shares								(6,018,000)
Issuance of common stock under stock option and stock purchase plans	314,649	314,649		3	306,982			7,664
Issuance of common stock under stock option and stock purchase plans, shares				5,458,000				162,000
Issuance of common stock under stock award plan	(50,953)	(50,953)		1	(50,954)
Issuance of common stock under stock award plan, shares				1,482,000
Compensation expense related to share-based payments	117,347	117,347			117,347
Tax benefit from share-based payments	50,383	50,383			50,383
Acquisitions of noncontrolling interests	187,337	125,641			125,641				61,696
Conversion of preferred stock	0	0		0	0
Conversion of preferred stock, shares			(8,000)	493,000
Recharacterization of share-based awards from equity to cash-settled due to restructuring	8,172	8,172			8,172
Ending Balance at Dec. 31, 2011	6,426,987	6,425,499	0	128	4,185,048	(26,535)	3,106,761	(839,903)	1,488
Ending Balance, shares at Dec. 31, 2011			0	255,633,000				(13,518,000)
Net income	1,380,033	1,380,033					1,380,033		0
Other comprehensive income, net of tax	(28,705)	(28,770)				(28,770)			65
Distributions to noncontrolling interests	1,199	0							1,199
Capital contribution from noncontrolling interests	73	0							73
Deconsolidation of noncontrolling interests	(556)	(3)			(3)				(553)
Repurchase of common stock for Treasury pursuant to the 2011 share repurchase plan, at cost	(984,715)	(984,715)						(984,715)
Repurchase of common stock for Treasury pursuant to the 2011 stock repurchase plan, at cost, shares	(7,800,000)							(7,811,000)
Retirement Of Common Stock	0	0		2	499,998			(500,000)
Retirement Of Common Stock Shares				3,674,000				(3,674,000)
Issuance of common stock under stock option and stock purchase plans	67,493	67,493		0	67,493
Issuance of common stock under stock option and stock purchase plans, shares				1,039,000
Issuance of common stock under stock award plan	(71,357)	(71,357)		1	(71,358)
Issuance of common stock under stock award plan, shares				1,239,000
Compensation expense related to share-based payments	123,956	123,956			123,956
Tax benefit from share-based payments	49,387	49,387			49,387
Ending Balance at Dec. 31, 2012	6,963,795	6,961,523	0	127	3,854,525	(55,305)	4,486,794	(1,324,618)	2,272
Ending Balance, shares at Dec. 31, 2012			0	254,237,000				(17,655,000)
Net income	1,862,341	1,862,341					1,862,341		0
Other comprehensive income, net of tax	27,560	27,560				27,560			0
Deconsolidation of noncontrolling interests	(1,676)	0							(1,676)
Repurchase of common stock for Treasury pursuant to the 2011 share repurchase plan, at cost	(400,309)	(400,309)						(400,309)
Repurchase of common stock for Treasury pursuant to the 2011 stock repurchase plan, at cost, shares	(2,000,000)							(1,986,000)
Issuance of common stock under stock option and stock purchase plans	66,770	66,770		0	66,770
Issuance of common stock under stock option and stock purchase plans, shares				767,000
Issuance of common stock under stock award plan	(89,746)	(89,746)		1	(89,747)
Issuance of common stock under stock award plan, shares	523,000			969,000
Compensation expense related to share-based payments	146,210	146,210			146,210
Tax benefit from share-based payments	45,893	45,893			45,893
Ending Balance at Dec. 31, 2013	$ 8,620,838	$ 8,620,242	$ 0	$ 128	$ 4,023,651	$ (27,745)	$ 6,349,135	$ (1,724,927)	$ 596
Ending Balance, shares at Dec. 31, 2013			0	255,973,000				(19,641,000)