Income Taxes - Schedule of Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current, Federal	$ 759	$ 1,067	$ 1,129
Current, State	149	120	125
Current, Foreign	23	19	37
Deferred, Federal	9	423	75
Deferred, State	13	3	(5)
Deferred, Foreign	(7)	6	17
Provision for income taxes	$ 946	$ 1,638	$ 1,378