Supplemental Financial Information - Trade Receivables, Allowances for Doubtful Accounts and Cash Discounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 58	$ 67	$ 62
Additions charged to costs and expenses	89	68	60
Deductions and other	(61)	(76)	(55)
Ending Balance	86	58	67
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	54	61	53
Additions charged to costs and expenses	31	25	23
Deductions and other	(11)	(32)	(14)
Ending Balance	75	54	61
Allowance for Cash Discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	4	6	9
Additions charged to costs and expenses	58	43	37
Deductions and other	(50)	(45)	(40)
Ending Balance	$ 12	$ 4	$ 6