Supplemental Financial Information - Trade Receivables, Allowances for Doubtful Accounts and Cash Discounts (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	$ 67	$ 62	$ 42
Additions charged to costs and expenses	68	60	80
Deductions and other	(76)	(55)	(61)
Ending Balance	58	67	62
Allowance for Doubtful Accounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	61	53	30
Additions charged to costs and expenses	25	23	33
Deductions and other	(32)	(14)	(11)
Ending Balance	54	61	53
Allowance for Cash Discounts
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning Balance	6	9	12
Additions charged to costs and expenses	43	37	47
Deductions and other	(45)	(40)	(50)
Ending Balance	$ 4	$ 6	$ 9