Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current income tax expense:
Federal	$ 195	$ 257	$ 228
State	89	21	105
Foreign	10	(4)	7
Total current expense	294	274	340
Deferred income tax expense (benefit):
Federal	(173)	(49)	58
State	(64)	52	24
Foreign	(5)	22	(3)
Total deferred expense	(242)	25	79
Total income tax expense	$ 52	$ 299	$ 419