Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal				$ 2,384	$ 3,012	$ 1,999
State				179	183	130
Foreign				195	123	96
Total current tax expense				2,758	3,318	2,225
Deferred:
Federal				(414)	(800)	(240)
State				(18)	(17)	(14)
Foreign				(25)	5	(1)
Total deferred tax benefit				(457)	(812)	(255)
Provision for income taxes	$ 537	$ 471	$ 328	$ 2,301	$ 2,506	$ 1,970