Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
U.S. federal income taxes:
Current	$ 373	$ 1,117	$ 756
Deferred	(15)	(10)	(224)
Total U.S. federal income taxes	358	1,107	532
Foreign income taxes:
Current	358	296	290
Deferred	49	102	(5)
Total foreign income taxes	407	398	285
State income taxes:
Current	66	106	90
Deferred	0	(28)	(34)
Total state income taxes	66	78	56
Total provision for income taxes	$ 831	$ 1,583	$ 873