Income Taxes - Components of Income Tax Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Federal
Current	$ 493	$ 613	$ 1,024	$ 914
Deferred	(37)	(154)	(157)	(47)
Federal income tax	456	459	867	867
State
Current	81	37	146	127
Deferred	14	46	37	52
State income tax	95	83	183	179
Applicable income taxes	$ 551	$ 542	$ 1,050	$ 1,046