Income Taxes - Components of Income Tax Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Federal
Current	$ 385	$ 455	$ 931	$ 1,479
Deferred	(53)	54	(17)	(103)
Federal income tax	332	509	914	1,376
State
Current	141	53	295	199
Deferred	(13)	27	54	64
State income tax	128	80	349	263
Applicable income taxes	$ 460	$ 589	$ 1,263	$ 1,639