Income Taxes - Components of Income Tax Expense (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Federal
Current	$ 613	$ 419	$ 914	$ 799
Deferred	(154)	13	(47)	33
Federal income tax	459	432	867	832
State
Current	37	96	127	180
Deferred	46		52	(5)
State income tax	83	96	179	175
Applicable income taxes	$ 542	$ 528	$ 1,046	$ 1,007