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, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Gain on settlements	$ 13
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		$ 14	$ (4)	$ (9)
Net changes recognized in Total other comprehensive (income) loss		14	(4)	(9)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		(16)		(35)
Prior service (credit) cost		3
Amortization of prior service credit		(2)
Amortization of prior unrecognized loss		(2)	(3)	(5)
Loss on divestiture		(2)
Gain on settlements		7
Net changes recognized in Total other comprehensive (income) loss		(12)	(3)	(40)
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses			(2)	(3)
Amortization of prior service credit		2	3	3
Amortization of prior unrecognized loss		1	1
Net changes recognized in Total other comprehensive (income) loss		3	2
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		2	(1)	(1)
Net changes recognized in Total other comprehensive (income) loss		$ 2	$ (1)	$ (1)