Income Taxes (Reconciliation of Unrecognized Tax Benefits Roll Forward) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance at January 1	$ 132	$ 106	$ 98
Increases-prior period positions	5	76	8
Decreases-prior period positions	0	(53)	0
Increases-current period positions	1	3	0
Balance at December 31	$ 138	$ 132	$ 106