Income Taxes - Components of Provision for Income Taxes, Net (Details) - USD ($) $ 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
Current taxes:
U.S. Federal									$ (129)	$ (137)	$ 1,136
U.S. State									322	211	208
International									563	724	327
Current taxes									756	798	1,671
Deferred taxes:
U.S. Federal									565	(202)	116
U.S. State									5	(26)	(31)
International									(129)	199	(331)
Deferred taxes									441	(29)	(246)
Provision for income taxes, net	$ 327	$ 508	$ 74	$ 287	$ 16	$ 58	$ 467	$ 229	$ 1,197	$ 769	$ 1,425