Stockholders' Equity - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 31, 2013
Class of Stock [Line Items]
Amount of common stock repurchases authorized				$ 750,000,000
Value of shares repurchased during period	268,647,000	160,418,000	141,468,000
Remaining amount available for future purchases of shares under approved repurchase program.	433,600,000
Common Stock
Class of Stock [Line Items]
Repurchases of common stock (in shares)	4,629,000	3,900,000	4,400,000
Value of shares repurchased during period	$ 268,600,000	$ 160,400,000	$ 141,500,000