Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current income tax expense:
Federal	$ 228	$ 114	$ 199
State	105	61	38
Foreign	7	14	14
Total current expense	340	189	251
Deferred income tax expense (benefit):
Federal	58	4	63
State	24	(15)	31
Foreign	(3)	(9)	3
Total deferred expense	79	(20)	97
Total income tax expense	$ 419	$ 169	$ 348