Income Taxes - Reconciliation of Beginning and Ending Amounts of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Beginning balance	$ 168	$ 168	$ 205
Additions based on tax positions taken in the current year	2	2	19
Additions based on tax positions of prior years	1	1	36
Reductions based on tax positions of prior years	(2)	(1)	(78)
Reductions due to settlements with taxing authorities	(1)	0	(10)
Reductions due to lapses in statutes of limitation	(2)	(2)	(4)
Ending balance	$ 166	$ 168	$ 168