Share-Based Payments (Tables)

12 Months Ended

Dec. 31, 2014

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)	2014			2013			2012
Research and development	$	102.1		$	95.6		$	74.7
Selling, general and administrative	150.3			160.3			109.6
Subtotal	252.4			255.9			184.3
Capitalized share-based compensation costs	(10.0		)	(9.8		)	(5.4		)
Share-based compensation expense included in total cost and expenses	242.4			246.1			178.9
Income tax effect	(72.2		)	(73.3		)	(53.4		)
Share-based compensation expense included in net income attributable to Biogen Idec Inc.	$	170.2		$	172.8		$	125.5

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

	For the Years Ended December 31,
(In millions)	2014			2013			2012
Stock options	$	—		$	0.6		$	2.3
Market stock units	37.4			32.8			23.3
Time-vested restricted stock units	115.4			103.5			93.0
Performance-vested restricted stock units settled in shares	—			—			0.1
Cash settled performance units	65.5			109.8			60.4
Performance units	21.9			—			—
Employee stock purchase plan	12.2			9.2			5.2
Subtotal	252.4			255.9			184.3
Capitalized share-based compensation costs	(10.0		)	(9.8		)	(5.4		)
Share-based compensation expense included in total cost and expenses	$	242.4		$	246.1		$	178.9

Stock option activity

	Shares		Weighted Average Exercise Price
Outstanding at December 31, 2013	384,000		$	55.49
Granted	—		$	—
Exercised	(163,000	)	$	53.46
Cancelled	—		$	—
Outstanding at December 31, 2014	221,000		$	56.98

Tax benefit and cash received from stock option exercises

	For the Years Ended December 31,
(In millions)	2014		2013		2012
Tax benefit realized for stock options	$	13.0	$	29.4	$	20.9
Cash received from the exercise of stock options	$	8.5	$	28.1	$	38.8

Market stock units activity

	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2013	550,000		$	128.04
Granted (a)	246,000		$	395.22
Vested	(363,000	)	$	107.89
Forfeited	(30,000	)	$	192.85
Unvested at December 31, 2014	403,000		$	219.29

Assumptions used in valuation of market based stock units

	For the Years Ended December 31,
	2014	2013
Expected dividend yield	—%	—%
Range of expected stock price volatility	31.7% - 35.1%	21.7% - 25.7%
Range of risk-free interest rates	0.1% - 0.7%	0.1% - 0.7%
30 calendar day average stock price on grant date	$280.88 - $335.65	**
60 calendar day average stock price on grant date	**	$150.33 - $240.14
Weighted-average per share grant date fair value	$395.22	$193.45

Cash settled performance shares activity

	Shares
Unvested at December 31, 2013	514,000
Granted (a)	177,000
Vested	(316,000	)
Forfeited	(40,000	)
Unvested at December 31, 2014	335,000

Performance units activity

	Shares
Unvested at December 31, 2013	—
Granted	57,000
Vested	—
Forfeited	—
Unvested at December 31, 2014	57,000

Time-vested restricted stock units activity

	Shares		Weighted Average Grant Date Fair Value
Unvested at December 31, 2013	1,660,000		$	135.95
Granted (a)	464,000		$	321.72
Vested	(885,000	)	$	117.74
Forfeited	(102,000	)	$	193.24
Unvested at December 31, 2014	1,137,000		$	221.01

Shares issued under employee stock purchase plan

	For the Years Ended December 31,
(In millions, except share amounts)	2014		2013		2012
Shares issued under ESPP	180,000		245,000		274,000
Cash received under ESPP	$	46.4	$	38.7	$	28.7