Quarterly Financial Data (unaudited) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Data [Abstract]
Total revenue	$ 1,878	$ 1,707	$ 1,515	$ 1,354	$ 1,305	$ 1,261	$ 1,191	$ 1,097	$ 6,454	$ 4,854	$ 3,344
Income before income taxes	167	231	225	214	120	208	265	222	837	815	883
Net income	$ 131	$ 179	$ 186	$ 150	$ 59	$ 158	$ 175	$ 145	$ 646	$ 537	$ 566