Income Tax - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Income Taxes [Line Items]
Net discrete tax (benefits) expense related to tax settlements	$ (1,000,000)	$ (1,000,000)	$ 1,000,000	$ (11,000,000)
Changes in uncertain tax positions				5,000,000
Net tax benefit related to result of changes in non-us tax laws				6,000,000
Uncertain tax positions from expirations of statute of limitations		$ 2,000,000	$ 1,000,000	$ 8,000,000
Maximum [Member]
Income Taxes [Line Items]
Uncertain tax positions from expirations of statute of limitations	$ 1,000,000
Earliest Tax Year [Member] | United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination			2017
Latest Tax Year [Member] | United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination			2019
State Tax Authorities [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination			2005
State Tax Authorities [Member] | Latest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination			2019
Non-U.S. Jurisdictions [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination			2003
Non-U.S. Jurisdictions [Member] | Latest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination			2020