Schedule II - Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 119
Balance at End of Year	170	$ 119
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	36	43	$ 80
Charged to Costs and Expenses	15	22	10
Deductions	(26)	(29)	(47)
Balance at End of Year	$ 25	$ 36	$ 43