Employee Benefit Plans - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) Plan	Jun. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($) Plan	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plans expenses				$ 20,000,000	$ 19,000,000	$ 18,000,000
Number of foreign defined benefit plans | Plan	1			1
Reduction in net pension obligations				$ 30,000,000
Pre-tax gain from net pension obligations	$ 7,000,000			7,000,000
Additional charge on defined benefit plan actuarial gain (loss)				$ 3,000,000
Pay out period for additional charge payment				5 years
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Net losses on curtailments and settlements					(1,000,000)	$ (1,000,000)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contribution	10,000,000			$ 10,000,000
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss amortized from AOCI to net periodic benefit cost			$ 3,000,000
Amortization of estimated prior service credits			0
Scenario, Forecast [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement medical benefits			$ 4,000,000
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	157,000,000			$ 157,000,000	143,000,000
Gain on settlements	$ 13,000,000
Weighted-average assumed health care cost trend rate	6.50%			6.50%
U.S. Defined Benefit Plans [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				32.00%
U.S. Defined Benefit Plans [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				68.00%
U.S. Defined Benefit Plans [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
One percentage point change effect on postretirement benefit obligation				$ 1,000,000
U.S. Defined Benefit Plans [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations	$ (13,000,000)			(13,000,000)	1,000,000
Net losses on curtailments and settlements				(1,000,000)	(5,000,000)
U.S. Defined Benefit Plans [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations	6,000,000			6,000,000	7,000,000
Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 205,000,000			$ 205,000,000	349,000,000
Weighted-average assumed health care cost trend rate	6.90%			6.90%
One percentage point change effect on postretirement benefit obligation				$ 3,000,000
Foreign Plans [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				49.00%
Foreign Plans [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				41.00%
Foreign Plans [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				6.00%
Foreign Plans [Member] | Cash and Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				4.00%
Foreign Plans [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations	$ (36,000,000)			$ (36,000,000)	(49,000,000)
Net losses on curtailments and settlements				(134,000,000)	(2,000,000)
Gain on settlements				7,000,000
Foreign Plans [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations	$ (6,000,000)			$ (6,000,000)	$ (4,000,000)
U.K. Plan [Member] | Other Nonoperating Income (Expense) [Member]
Defined Benefit Plan Disclosure [Line Items]
Charge on effect of accued benefit		$ 2,000,000