Income Taxes - Components of Income Tax Expense (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Federal
Current	$ 301	$ 380
Deferred	107	20
Federal income tax	408	400
State
Current	90	84
Deferred	6	(5)
State income tax	96	79
Applicable income taxes	$ 504	$ 479