Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss), Pre-Tax (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
(Loss) gain on settlements	$ (3)
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		$ (4)	$ 14	$ (4)
(Loss) gain on settlements		(3)
Net changes recognized in Total other comprehensive (income) loss		(7)	14	(4)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		8	(16)
Prior service (credit) cost			3
Amortization of prior service credit			(2)
Amortization of prior unrecognized loss		(3)	(2)	(3)
Loss on divestiture			(2)
(Loss) gain on settlements		(1)	7
Net changes recognized in Total other comprehensive (income) loss		4	(12)	(3)
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		1		(2)
Amortization of prior service credit			2	3
Amortization of prior unrecognized loss		1	1	1
Net changes recognized in Total other comprehensive (income) loss		2	3	2
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		(1)	2	(1)
Amortization of prior unrecognized loss		(1)
Net changes recognized in Total other comprehensive (income) loss		$ (2)	$ 2	$ (1)