Income Taxes - Schedule of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Beginning Balance	$ 522	$ 390
Additions (reductions) based on tax positions related to the current year	(3)	29
Additions for tax positions of prior years	13	119
Reductions for tax positions of prior years	(30)	(3)
Settlements	(22)	0
Lapse of applicable statutes of limitations	(11)	(13)
Ending Balance	$ 469	$ 522