Stock Repurchases (Details) - USD ($) shares in Millions		12 Months Ended
	Oct. 20, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Oct. 31, 2014	Dec. 31, 2012
Stockholders' Equity Note [Abstract]
Authorized amount for share repurchase		$ 1,400,000,000.0			$ 700,000,000.0	$ 300,000,000.0
Remaining authorized amount for share repurchase		$ 396,200,000
Accelerated share repurchase program announced	$ 450,000,000
Treasury stock purchases, shares		0.5	5.2
Repurchases of common stock		$ 0	$ 550,300,000	$ 125,000,000
Repurchased shares to satisfy minimum withholding obligations (in shares)		0.3	0.2
Repurchased shares to satisfy employee withholding tax obligations		$ 32,000,000	$ 22,400,000	$ 12,000,000