Changes in 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	$ 54	$ 61	$ 63
Additions based on tax positions related to the current year	4	6	8
Reductions for tax positions for prior years	(1)	(8)	(6)
Settlements	(3)	(4)	(3)
Statute of limitations	0	(1)	(1)
Ending Balance	$ 57	$ 54	$ 61