Shareholders' Equity - Shares Repurchased (Details) - USD ($)	1 Months Ended	3 Months Ended							9 Months Ended		10 Months Ended	12 Months Ended		34 Months Ended
	Nov. 05, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Nov. 05, 2015	Dec. 31, 2014	Dec. 31, 2013	Nov. 05, 2015	May. 06, 2015
Equity, Class of Treasury Stock [Line Items]
Repurchases of common stock									$ 420,000,000	$ 438,000,000
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Shares repurchased		5,362,103	4,737,388	5,860,291	6,388,187	9,623,309	7,051,842	1,350,443	15,959,782			24,413,781	12,512,759
Repurchases of common stock		$ 135,000,000	$ 133,000,000	$ 152,000,000	$ 152,000,000	$ 226,000,000	$ 177,000,000	$ 35,000,000	$ 420,000,000			$ 590,000,000	$ 264,000,000
Average price paid (in dollars per share)		$ 25.17	$ 28.13	$ 25.87	$ 23.83	$ 23.47	$ 25.14	$ 25.92	$ 26.31			$ 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	1,750,310										17,710,092			54,636,632
Repurchases of common stock	$ 48,000,000										$ 468,000,000			$ 1,322,000,000
Average price paid (in dollars per share)	$ 27.16										$ 26.39			$ 24.19
Remaining capacity of shares repurchase program	$ 143,000,000										$ 143,000,000			$ 143,000,000