Income Taxes - Schedule of Significant Components of Provision for Income Taxes Attributable to Continuing Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current income tax provision:
Federal taxes	$ 1,585	$ 2,087	$ 1,991
State taxes	223	209	207
International taxes	133	104	73
Total current provision	1,941	2,400	2,271
Deferred income tax (benefit) provision:
Federal taxes	1,509	(621)	(368)
State taxes	(69)	(63)	(39)
International taxes	(6)	(2)	5
Total deferred (benefit) provision	1,434	(686)	(402)
Income tax provision (benefit)	$ 3,375	$ 1,714	$ 1,869