Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss), Pre-Tax (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses	$ (4)	$ (9)	$ 7
Net changes recognized in Total other comprehensive (income) loss	(4)	(9)	7
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		(35)	31
Amortization of prior unrecognized loss	(3)	(5)	(3)
Other			(1)
Net changes recognized in Total other comprehensive (income) loss	(3)	(40)	27
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses	(2)	(3)	2
Amortization of prior service credit	3	3	3
Amortization of prior unrecognized loss	1
Other			1
Net changes recognized in Total other comprehensive (income) loss	2		6
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses	(1)	(1)	5
Net changes recognized in Total other comprehensive (income) loss	$ (1)	$ (1)	$ 5