Comprehensive Income (Tables)

6 Months Ended

Jun. 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 June 30, 2011						Ended June 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	$	288.0	$	16.0	$	304.0	$	293.4		$	1.2		$	294.6
Unrealized gains (losses) on securities available for sale, net of tax of $0.6 and $3.8		1.1		—		1.1		(6.5	)		—			(6.5	)
Unrealized gains (losses) on foreign currency forward contracts, net of tax of $0.8 and $3.6		6.3		—		6.3		26.5			—			26.5
Unrealized gains (losses) on pension benefit obligation, net of tax of $0 and $0		—		—		—		(0.2	)		—			(0.2	)
Currency translation adjustment		19.3		2.9		22.2		(71.8	)		(3.4	)		(75.2	)
Comprehensive income (loss)	$	314.7	$	18.9	$	333.6	$	241.4		$	(2.2	)	$	239.2

	For the Six Months								For the Six Months
	Ended June 30, 2011								Ended June 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	$	582.4		$	30.4	$	612.8		$	510.9		$	3.8		$	514.7
Unrealized gains (losses) on securities available for sale, net of tax of $6.3 and $5.5		(10.7	)		—		(10.7	)		(9.4	)		—			(9.4	)
Unrealized gains (losses) on foreign currency forward contracts, net of tax of $1.2 and $6.5		(11.1	)		—		(11.1	)		54.3			—			54.3
Unrealized gains (losses) on pension benefit obligation, net of tax of $0 and $0		—			—		—			(0.3	)		—			(0.3	)
Currency translation adjustment		69.1			5.7		74.8			(124.2	)		(6.0	)		(130.2	)
Comprehensive income (loss)	$	629.7		$	36.1	$	665.8		$	431.3		$	(2.2	)	$	429.1

Stockholders' Equity attributable to Noncontrolling interest- roll forward

	For the Three Months						For the Six Months
	Ended June 30,						Ended June 30,
(In millions)	2011			2010			2011			2010
Noncontrolling interests, beginning of period	$	70.1		$	41.2		$	52.9		$	40.4
Net income attributable to noncontrolling interests		16.0			1.2			30.4			3.8
Translation adjustments		2.9			(3.4	)		5.7			(6.0	)
Distributions to noncontrolling interests		(9.9	)		—			(9.9	)		—
Capital contributions from noncontrolling interests		—			1.4			—			2.2
Noncontrolling interests, end of period	$	79.1		$	40.4		$	79.1		$	40.4