Income Taxes - Provision for Income Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Federal:
Current	$ 673	$ 955	$ 698
Deferred	(152)	(308)	(163)
Federal, total	521	647	535
State:
Current	65	81	84
Deferred	(58)	(70)	(23)
State, total	7	11	61
Foreign:
Current	206	228	192
Deferred	(24)	(18)	(16)
Foreign, total	182	210	176
Total provision for income taxes	$ 710	$ 868	$ 772