Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
Federal	$ 3,012	$ 1,999	$ 1,154
State	183	130	69
Foreign	123	96	68
Total current tax expense	3,318	2,225	1,291
Deferred:
Federal	(800)	(240)	(28)
State	(17)	(14)	(7)
Foreign	5	(1)	(2)
Total deferred tax benefit	(812)	(255)	(37)
Provision for income taxes	$ 2,506	$ 1,970	$ 1,254