Share Repurchases (Details) - USD ($) shares in Thousands	1 Months Ended	3 Months Ended
	Mar. 31, 2015	Aug. 01, 2015	Feb. 28, 2015	Dec. 31, 2013
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization				$ 300,000,000
Amount remaining under stock repurchase program		$ 40,000,000	$ 290,000,000
Value of initial shares	$ 187,500,000	$ 62,500,000
Accelerated Stock Repurchase Agreement [Member]
Equity, Class of Treasury Stock [Line Items]
Share repurchase authorization	$ 250,000,000
Number of shares of treasury stock	10,700	3,900
Merrill Lynch [Member]
Equity, Class of Treasury Stock [Line Items]
Payment for accelerated stock repurchase agreements	$ 125,000,000
Merrill Lynch [Member] | Accelerated Stock Repurchase Agreement [Member]
Equity, Class of Treasury Stock [Line Items]
Number of shares of treasury stock	5,350
JP Morgan [Member]
Equity, Class of Treasury Stock [Line Items]
Payment for accelerated stock repurchase agreements	$ 125,000,000
JP Morgan [Member] | Accelerated Stock Repurchase Agreement [Member]
Equity, Class of Treasury Stock [Line Items]
Number of shares of treasury stock	5,350