Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 400	$ 443	$ 192
State	56	88	50
Foreign	37	38	36
Current tax total	493	569	278
Deferred:
Federal	(316)	57	43
State	62	17	(17)
Foreign	3	(1)	4
Deferred tax total	(251)	73	30
Income tax expense	$ 242	$ 642	$ 308