Comprehensive Income (Tables)

9 Months Ended

Sep. 30, 2011

Equity and Comprehensive Income [Abstract]

Activities reflected in comprehensive income, included within equity attributable to the shareholders of Biogen Idec, equity attributable to noncontrolling interests, and total shareholders' equity

	For the Three Months									For the Three Months
	Ended September 30, 2011									Ended September 30, 2010
	Biogen Idec						Total			Biogen Idec						Total
	Shareholders’			Noncontrolling			Shareholders’			Shareholders’			Noncontrolling			Shareholders’
(In millions)	Equity			Interests			Equity			Equity			Interests			Equity
Comprehensive income:
Net income	$	351.8		$	1.9		$	353.7		$	254.1		$	(141.9	)	$	112.2
Unrealized gains (losses) on securities available for sale, net of tax of $0.8 and $3.4		(1.4	)		—			(1.4	)		5.8			—			5.8
Unrealized gains (losses) on foreign currency forward contracts, net of tax of $3.8 and $8.0		32.9			—			32.9			(71.1	)		—			(71.1	)
Unrealized gains (losses) on pension benefit obligation, net of tax of $0 and $0		—			—			—			0.2			—			0.2
Currency translation adjustment		(49.7	)		(0.8	)		(50.5	)		84.4			4.5			88.9
Comprehensive income (loss)	$	333.6		$	1.1		$	334.7		$	273.4		$	(137.4	)	$	136.0

	For the Nine Months								For the Nine Months
	Ended September 30, 2011								Ended September 30, 2010
	Biogen Idec					Total			Biogen Idec						Total
	Shareholders’			Noncontrolling		Shareholders’			Shareholders’			Noncontrolling			Shareholders’
(In millions)	Equity			Interests		Equity			Equity			Interests			Equity
Comprehensive income:
Net income	$	934.2		$	32.3	$	966.5		$	765.0		$	(138.2	)	$	626.8
Unrealized gains (losses) on securities available for sale, net of tax of $7.1 and $2.1		(12.1	)		—		(12.1	)		(3.6	)		—			(3.6	)
Unrealized gains (losses) on foreign currency forward contracts, net of tax of $2.6 and $1.5		21.9			—		21.9			(16.8	)		—			(16.8	)
Unrealized gains (losses) on pension benefit obligation, net of tax of $0 and $0		—			—		—			(0.1	)		—			(0.1	)
Currency translation adjustment		19.3			4.9		24.2			(39.2	)		(1.3	)		(40.5	)
Comprehensive income (loss)	$	963.3		$	37.2	$	1,000.5		$	705.3		$	(139.5	)	$	565.8

Stockholders' Equity attributable to Noncontrolling interest- roll forward

	For the Three Months						For the Nine Months
	Ended September 30,						Ended September 30,
(In millions)	2011			2010			2011			2010
Noncontrolling interests, beginning of period	$	79.1		$	40.5		$	52.9		$	40.4
Fair value of assets and liabilities acquired and assigned to noncontrolling interest (Note 18)		—			145.0			—			145.0
Net income (loss) attributable to noncontrolling interests		1.9			(141.9	)		32.3			(138.2	)
Translation adjustments		(0.8	)		4.5			4.9			(1.3	)
Distributions to noncontrolling interests		(14.1	)		(8.9	)		(24.0	)		(8.9	)
Capital contributions from noncontrolling interests		—			0.3			—			2.5
Acquisition of noncontrolling interests (Note 2)		(61.7	)		—			(61.7	)		—
Noncontrolling interests, end of period	$	4.4		$	39.5		$	4.4		$	39.5