Valuation and Qualifying Accounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reserves for Doubtful Accounts [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance Beginning of Year	$ 24	$ 25	$ 31
Charged to Income	43	42	36
Accounts Written Off/Use of Reserve	(45)	(43)	(42)
Balance End of Year	22	24	25
Merger and Restructuring Accruals [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance Beginning of Year	7	13	45
Charged to Income		4	15
Accounts Written Off/Use of Reserve	(5)	(10)	(47)
Balance End of Year	$ 2	$ 7	$ 13