Valuation And Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 38	$ 34	$ 34
Expensed	29	27	24
Other Adjustments	3	(2)	(3)
Deductions	(34)	(21)	(21)
Balance at End of Period	36	38	34
Tax Valuation Allowance
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	357	351	319
Expensed	0	17	20
Other Adjustments	13	3	12
Deductions	(39)	(14)	0
Balance at End of Period	$ 331	$ 357	$ 351