Income Taxes - Components of Income Tax Expense (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Federal
Current	$ 234	$ 531
Deferred	19	(120)
Federal income tax	253	411
State
Current	92	65
Deferred	17	23
State income tax	109	88
Applicable income taxes	$ 362	$ 499