Quarterly Supplementary Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenues	$ 710	$ 1,915	$ 1,558	$ 1,224	$ 1,411	$ 1,412	$ 1,386	$ 1,523	$ 5,407	$ 5,732	$ 5,449
Income (loss) before income taxes	(581)	618	264	(50)	197	129	128	276	251	730	812
Net Income (Loss) Attributable to Parent	$ (452)	$ 553	$ 217	$ (31)	$ 642	$ 102	$ 100	$ 201	$ 287	$ 1,045	$ 591
Basic (in usd per share)	$ (2.78)	$ 3.40	$ 1.33	$ (0.19)	$ 3.92	$ 0.62	$ 0.61	$ 1.22	$ 1.76	$ 6.36	$ 3.59
Diluted (in usd per share)	$ (2.78)	$ 3.38	$ 1.32	$ (0.19)	$ 3.88	$ 0.61	$ 0.60	$ 1.21	$ 1.75	$ 6.29	$ 3.55