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, 2021	Sep. 30, 2020	Sep. 30, 2019
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlements or curtailments cost	$ (3)
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		$ (2)	$ (4)	$ 14
Settlements or curtailments cost		(4)	(3)
Net changes recognized in Total other comprehensive (income) loss		(6)	(7)	14
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		(15)	8	(16)
Prior service (credit) cost		(1)		3
Amortization of prior service credit				(2)
Amortization of prior unrecognized loss		(3)	(3)	(2)
Loss on divestiture				(2)
Settlements or curtailments cost		(1)	(1)	7
Net changes recognized in Total other comprehensive (income) loss		(20)	4	(12)
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses			1
Amortization of prior service credit				2
Amortization of prior unrecognized loss			1	1
Net changes recognized in Total other comprehensive (income) loss			2	3
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		(2)	(1)	2
Amortization of prior unrecognized loss			(1)
Net changes recognized in Total other comprehensive (income) loss		$ (2)	$ (2)	$ 2