Employee Benefit Plans - Amounts Recognized in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ (7)
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	13	$ (1)
Balance in accumulated other comprehensive income (loss), pretax	13	(1)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	36	49
Net prior service credit		(1)
Balance in accumulated other comprehensive income (loss), pretax	36	48
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	(6)	(7)
Net prior service credit		(2)
Balance in accumulated other comprehensive income (loss), pretax	(6)	(9)
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	6	4
Balance in accumulated other comprehensive income (loss), pretax	$ 6	$ 4