Valuation And Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 52	$ 39	$ 36
Expensed	(73)	(41)	(34)
Other Adjustments	(3)	0	2
Deductions	(68)	(28)	(29)
Balance at End of Period	60	52	39
Tax Valuation Allowance
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	214	311	331
Expensed	(1)	(95)	3
Other Adjustments	6	(2)	17
Deductions	0	0	0
Balance at End of Period	$ 207	$ 214	$ 311