Employee Benefit Plans - Fair Value of Pension Plan Assets by Asset Category (Detail) - USD ($) $ in Millions		Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		$ 300	$ 346
Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		107	10
Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		184	328
Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		5	6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		111	164
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		106	9
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	152
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			1
Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		189	182
Significant Observable Inputs (Level 2) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		183	176
Significant Observable Inputs (Level 2) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		5	5
Cash and Cash Equivalent Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		4	2
Cash and Cash Equivalent Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		4	2
U.S. Government Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		12
U.S. Government Bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		12
U.S. Corporate Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		84
U.S. Corporate Bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		84
Non-U.S. Equities [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		4	3
Non-U.S. Equities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		4	3
Equity Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	76	74
Equity Funds [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	76	74
Non-U.S. Government Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		2	2
Non-U.S. Government Bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		2	2
Fixed Income Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[2]	95	194
Fixed Income Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[2]		104
Fixed Income Funds [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[2]	95	90
Non-U.S. Corporate Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		3	3
Non-U.S. Corporate Bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		3	3
Real Estate [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[3]	12	12
Real Estate [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[3]	12	12
Mortgage Backed Securities [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Mortgage Backed Securities [Member] | Significant Observable Inputs (Level 2) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Other Fixed Income [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Other Fixed Income [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Cash Equivalent Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	48
Cash Equivalent Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	48
Insurance Contracts [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[4]	5	5
Insurance Contracts [Member] | Significant Observable Inputs (Level 2) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[4]	$ 5	5
Other Alternative Investments [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			1
Other Alternative Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			$ 1

[1] The equity funds asset class includes funds that invest in U.S. equities as well as equity securities issued by companies incorporated, listed or domiciled in countries in developed and/or emerging markets. These companies may be in the small-, mid- or large-cap categories.

[2] The fixed income funds asset class includes investments in high quality funds. High quality fixed income funds primarily invest in low risk U.S. and non-U.S. government securities, investment-grade corporate bonds, mortgages and asset-backed securities. A significant portion of the fixed income funds include investment in long-term bond funds.

[3] The real estate funds asset class includes funds that primarily invest in entities which are principally engaged in the ownership, acquisition, development, financing, sale and/or management of income-producing real estate properties, both commercial and residential. These funds typically seek long-term growth of capital and current income that is above average relative to public equity funds.

[4] Insurance contracts held by the Company’s non-U.S. plans are issued by well-known, highly rated insurance companies.