Employee Benefit Plans - Additional Information (Detail)	3 Months Ended			6 Months Ended
	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2020 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2019 Plan
Defined Benefit Plan Disclosure [Line Items]
Number of foreign defined benefit plans | Plan						1
Pre-tax gain from net pension obligations			$ 6,000,000
Additional charge on defined benefit plan actuarial gain (loss)			$ 3,000,000
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan termination settlements expected future loss				$ 13,000,000
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Other postretirement benefit costs (gains)	$ 1,000,000	$ (1,000,000)		$ 1,000,000	$ (1,000,000)