Employee Benefit Plans - Amounts Recognized in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
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	$ 6	13
Balance in accumulated other comprehensive income (loss), pretax	6	13
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	40	36
Balance in accumulated other comprehensive income (loss), pretax	40	36
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	(4)	(6)
Balance in accumulated other comprehensive income (loss), pretax	(4)	(6)
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	4	6
Balance in accumulated other comprehensive income (loss), pretax	$ 4	$ 6