Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Taxes [Line Items]
Net operating loss carryforwards	$ 254	$ 257	$ 254
Other deferred tax assets	51	42	51
Valuation allowance	481	470	481
NOLs		1,265
Other tax credit carryforwards		118
Undistributed earnings		1,934
Unrecognized tax benefits	23	21	23	$ 27	$ 37
Unrecognized tax benefits, offset against deferred tax assets		15
Accruals for penalties and interest		4
Total penalties and interest		1	1	$ 2
Favorable impact on tax provision		$ 21
Earliest Tax Year [Member] | United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination		2018
Latest Tax Year [Member] | United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination		2020
Other Liabilities [Member]
Income Taxes [Line Items]
Unrecognized tax benefits, recorded		$ 6
Non-U.S. Jurisdictions [Member]
Income Taxes [Line Items]
NOLs		$ 26
Non-U.S. Jurisdictions [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination		2005
Non-U.S. Jurisdictions [Member] | Latest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination		2020
Non-U.S. Jurisdictions [Member] | Maximum [Member]
Income Taxes [Line Items]
Other tax credit carryforwards		$ 1
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		2020
U.S. Defined Benefit Plans [Member]
Income Taxes [Line Items]
Deferred tax assets, valuation allowance charge	228		228
Increased/(decreased) valuation allowance		$ 11
Non-U.S Subsidiaries [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	145		145
Other deferred tax assets	19		19
Valuation allowance	164		164
Non-U.S Subsidiaries [Member] | Previously Reported [Member]
Income Taxes [Line Items]
Net operating loss carryforwards	109		109
Other deferred tax assets	32		32
Valuation allowance	$ 317		$ 317