Stockholders' Equity (Narrative) (Details) (USD $)	12 Months Ended			1 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	May 31, 2012	Sep. 30, 2014	Feb. 28, 2015
Class of Stock [Line Items]
Shares withheld for the payment of taxes	279,680	235,922	560,484
Authorized share repurchase						$ 500,000,000
Stock repurchase program, value	444,400,000
Value of shares withheld related to tax withholding for share-based compensation	11,400,000	11,300,000	22,400,000
Parent
Class of Stock [Line Items]
Structured stock repurchase agreement				8,600,000	100,000,000.0
Subsequent Event [Member]
Class of Stock [Line Items]
Authorized share repurchase							500,000,000
Stock repurchase program, value							$ 425,000,000