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, 2011	$ (6,426,987)	$ (6,425,499)	$ 0	$ (128)	$ (4,185,048)	$ 26,535	$ (3,106,761)	$ (839,903)	$ (1,488)
Beginning 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)
Distribution to noncontrolling interests	1,199	0							1,199
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								(7,811,000)
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
Stock Issued During Period, Value, Stock Options Exercised	(71,357)	(71,357)		(1)	(71,358)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				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
Capital contributions from noncontrolling interests	73	0							73
Noncontrolling Interest, Decrease from Deconsolidation	(556)	(3)			(3)				(553)
Retirement of common stock pursuant to the 2011 share repurchase plan, at cost	0	0		(2)	(499,998)			(500,000)
Retirement of common stock pursuant to the 2011 share repurchase plan, shares				(3,674,000)				(3,674,000)
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
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
Stock Issued During Period, Value, Stock Options Exercised	(89,746)	(89,746)		(1)	(89,747)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period				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
Noncontrolling Interest, Decrease from Deconsolidation	(1,676)	0							(1,676)
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)
Net income	2,941,565	2,934,784					2,934,784		6,781
Other comprehensive income, net of tax	(31,743)	(31,743)				(31,743)			0
Distribution to noncontrolling interests	(9,051)	0							(9,051)
Other transactions with noncontrolling interests	6,704	0							6,704
Repurchase of common stock for Treasury pursuant to the 2011 share repurchase plan, at cost	(886,779)	(886,779)						(886,779)
Repurchase of common stock for Treasury pursuant to the 2011 stock repurchase plan, at cost, shares	(2,900,000)							(2,921,000)
Issuance of common stock under stock option and stock purchase plans	54,887	54,887		0	54,887
Issuance of common stock under stock option and stock purchase plans, shares				342,000
Stock Issued During Period, Value, Stock Options Exercised	(140,352)	(140,352)		(1)	(140,353)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	163,000			811,000
Compensation expense related to share-based payments	165,004	165,004			165,004
Tax benefit from share-based payments	92,967	92,967			92,967
Ending Balance at Dec. 31, 2014	$ (10,814,040)	$ (10,809,010)	$ 0	$ (129)	$ (4,196,156)	$ (59,488)	$ (9,283,919)	$ (2,611,706)	$ (5,030)
Ending Balance, shares at Dec. 31, 2014			0	(257,126,000)				(22,562,000)