Income Taxes - Schedule of Provision for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Current, Federal	$ 1,021	$ 670	$ 759
Current, State	126	134	149
Current, Foreign	5	17	23
Deferred, Federal	(73)	254	9
Deferred, State	(39)	29	13
Deferred, Foreign	3	(5)	(7)
Provision for income taxes	$ 1,043	$ 1,099	$ 946