Stock Repurchases (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Stockholders' Equity Note [Abstract]
Stock repurchase program, authorized amount	$ 1,400,000,000
Remaining authorized repurchase amount	395,900,000
Shares repurchased for tax withholding	0.2
Payments for repurchase of shares for tax withholding	$ 20,500,000	$ 10,700,000