Supplemental Financial Information - Trade Receivables, Allowances for Doubtful Accounts and Cash Discounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 88	$ 86	$ 58
Additions charged to costs and expenses	78	125	89
Deductions and other	(73)	(123)	(61)
Ending Balance	94	88	86
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	75	75	54
Additions charged to costs and expenses	40	31	31
Deductions and other	(35)	(31)	(11)
Ending Balance	80	75	75
Allowance for Cash Discounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	13	12	4
Additions charged to costs and expenses	39	94	58
Deductions and other	(38)	(92)	(50)
Ending Balance	$ 14	$ 13	$ 12