Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
U.S. federal income taxes:
Current	$ 756	$ 503	$ 413
Deferred	(224)	8	121
Total U.S. federal income taxes	532	511	534
Foreign income taxes:
Current	290	310	163
Deferred	(5)	(11)	66
Benefit of net operating loss carryforwards	0	(48)	(13)
Total foreign income taxes	285	251	216
State income taxes:
Current	90	66	50
Deferred	(34)	(8)	9
Total state income taxes	56	58	59
Total provision for income taxes	$ 873	$ 820	$ 809