Income Taxes - Components of Income Tax Expense (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Federal
Current	$ 556	$ 423	$ 1,355	$ 1,334
Deferred	(114)	10	(81)	(19)
Federal income tax	442	433	1,274	1,315
State
Current	103	101	283	268
Deferred	(11)	(11)	(16)	(17)
State income tax	92	90	267	251
Applicable income taxes	$ 534	$ 523	$ 1,541	$ 1,566