Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Net revenues	$ 2,043	$ 1,618	$ 1,631	$ 1,726	$ 2,014	$ 1,568	$ 1,570	$ 1,455	$ 7,017	$ 6,608	$ 4,664
Cost of revenues	803	552	561	585	776	529	598	491
Operating income	221	257	339	493	425	294	232	461	1,309	1,412	1,319
Net income	$ (584)	$ 188	$ 243	$ 426	$ 254	$ 199	$ 151	$ 363	$ 273	$ 966	$ 892
Basic earnings per common share (in dollars per share)	$ (0.77)	$ 0.25	$ 0.32	$ 0.57	$ 0.34	$ 0.27	$ 0.20	$ 0.49	$ 0.36	$ 1.30	$ 1.21
Diluted earnings per common share (in dollars per share)	$ (0.77)	$ 0.25	$ 0.32	$ 0.56	$ 0.33	$ 0.26	$ 0.20	$ 0.48	$ 0.36	$ 1.28	$ 1.19