Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2013

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Share-based compensation expense included in consolidated statements of income

	For the Years Ended December 31,
(In millions)	2013			2012			2011
Research and development	$	95.6		$	74.7		$	62.0
Selling, general and administrative	160.3			109.6			88.7
Restructuring charges	—			—			(0.6		)
Subtotal	255.9			184.3			150.1
Capitalized share-based compensation costs	(9.8		)	(5.4		)	(4.5		)
Share-based compensation expense included in total cost and expenses	246.1			178.9			145.6
Income tax effect	(73.3		)	(53.4		)	(44.6		)
Share-based compensation expense included in net income attributable to Biogen Idec Inc.	$	172.8		$	125.5		$	101.0

Summary of share-based compensation expense associated with each of our share-based compensating programs

	For the Years Ended December 31,
(In millions)	2013			2012			2011
Stock options	$	0.6		$	2.3		$	5.9
Market stock units	32.8			23.3			14.6
Time-vested restricted stock units	103.5			93.0			89.6
Performance-vested restricted stock units settled in shares	—			0.1			1.0
Cash settled performance shares	109.8			60.4			32.7
Employee stock purchase plan	9.2			5.2			6.3
Subtotal	255.9			184.3			150.1
Capitalized share-based compensation costs	(9.8		)	(5.4		)	(4.5		)
Share-based compensation expense included in total cost and expenses	$	246.1		$	178.9		$	145.6

Stock option activity

	Shares		Weighted Average Exercise Price
Outstanding at December 31, 2012	907,000		$	54.48
Granted	—		$	—
Exercised	(523,000	)	$	53.73
Cancelled	—		$	—
Outstanding at December 31, 2013	384,000		$	55.49

Tax benefit and cash received from stock option exercises

	For the Years Ended December 31,
(In millions)	2013		2012		2011
Tax benefit realized for stock options	$	29.4	$	20.9	$	47.5
Cash received from the exercise of stock options	$	28.1	$	38.8	$	291.9

Market stock units activity

	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2012	606,000		$	94.73
Granted (a)	271,000		$	193.45
Vested	(296,000	)	$	85.12
Forfeited	(31,000	)	$	128.39
Unvested at December 31, 2013	550,000		$	128.04

Assumptions used in valuation of market based stock units

	For the Years Ended December 31,
	2013	2012
Expected dividend yield	—%	—%
Range of expected stock price volatility	21.7% - 25.7%	29.6% - 34.0%
Range of risk-free interest rates	0.1% - 0.7%	0.2% - 0.6%
60 calendar day average stock price on grant date	$150.33 - $240.14	$113.83 - $149.79
Weighted-average per share grant date fair value	$193.45	$134.95

Cash settled performance shares activity

	Shares
Unvested at December 31, 2012	592,000
Granted (a)	273,000
Vested	(317,000	)
Forfeited	(34,000	)
Unvested at December 31, 2013	514,000

Time-vested restricted stock units activity

	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2012	2,187,000		$	90.37
Granted (a)	758,000		$	176.53
Vested	(1,181,000	)	$	79.17
Forfeited	(104,000	)	$	119.42
Unvested at December 31, 2013	1,660,000		$	135.95

Performance-vested restricted stock units activity

	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2012	930		$	53.64
Granted	—		$	—
Vested	(930	)	$	53.64
Forfeited	—		$	—
Unvested at December 31, 2013	—		$	—

Shares issued under employee stock purchase plan

	For the Years Ended December 31,
(In millions, except share amounts)	2013		2012		2011
Shares issued under ESPP	245,000		274,000		434,000
Cash received under ESPP	$	38.7	$	28.7	$	22.8