Shareholders' Equity - Shares Repurchased (Details) - USD ($)	1 Months Ended	3 Months Ended						6 Months Ended		7 Months Ended	12 Months Ended		31 Months Ended
	Aug. 05, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2015	Jun. 30, 2014	Aug. 05, 2015	Dec. 31, 2014	Dec. 31, 2013	Aug. 05, 2015	May. 06, 2015
Equity, Class of Treasury Stock [Line Items]
Repurchases of common stock								$ (285,000,000)	$ (212,000,000)
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased		4,737,388	5,860,291	6,388,187	9,623,309	7,051,842	1,350,443	10,597,679			24,413,781	12,512,759
Repurchases of common stock		$ (133,000,000)	$ (152,000,000)	$ (152,000,000)	$ (226,000,000)	$ (177,000,000)	$ (35,000,000)	$ (285,000,000)			$ (590,000,000)	$ (264,000,000)
Average price paid (in dollars per share)		$ 28.13	$ 25.87	$ 23.83	$ 23.47	$ 25.14	$ 25.92	$ 26.88			$ 24.17	$ 21.12
Authorized repurchase amount														$ 400,000,000
Subsequent Event [Member] | Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased	1,817,605									12,415,284			49,341,824
Repurchases of common stock	$ (45,000,000)									$ (330,000,000)			$ (1,184,000,000)
Average price paid (in dollars per share)	$ 24.76									$ 26.57			$ 24.00
Remaining capacity of shares repurchase program	$ 280,000,000									$ 280,000,000			$ 280,000,000