Supplemental Financial Information - Trade Receivables, Allowances for Doubtful Accounts and Cash Discounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 86	$ 58	$ 67
Additions charged to costs and expenses	125	89	68
Deductions and other	(123)	(61)	(76)
Ending Balance	88	86	58
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	75	54	61
Additions charged to costs and expenses	31	31	25
Deductions and other	(31)	(11)	(32)
Ending Balance	75	75	54
Allowance for Cash Discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	12	4	6
Additions charged to costs and expenses	94	58	43
Deductions and other	(92)	(50)	(45)
Ending Balance	$ 13	$ 12	$ 4