Income Taxes - Income Tax Provision (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
Federal	$ 315	$ 331	$ 290
State	31	40	35
Foreign	11	10	12
Current income tax provision	357	381	337
Deferred:
Federal	22	(4)	(12)
State	(2)	6	1
Foreign	0	1	2
Deferred income tax provision	20	3	(9)
Income tax provision	$ 377	$ 384	$ 328