Employee Benefit Plans - Fair Value of Pension Plan Assets by Asset Category (Detail) - USD ($) $ in Millions		Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		$ 346	$ 472
Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		10	104
Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		328	349
Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		6	16
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		164	65
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		9	17
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		152	45
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		182	407
Significant Observable Inputs (Level 2) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	87
Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		176	304
Significant Observable Inputs (Level 2) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		5	16
Cash and Cash Equivalent Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		2	3
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		2	3
U.S. Government Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			30
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			17
U.S. Government Bonds [Member] | Significant Observable Inputs (Level 2) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			13
U.S. Corporate Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			74
U.S. Corporate Bonds [Member] | Significant Observable Inputs (Level 2) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			74
Non-U.S. Equities [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		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		3
Equity Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	74	170
Equity 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]		44
Equity Funds [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	74	126
Non-U.S. Government Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		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
Fixed Income Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[2]	194	169
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]	90	169
Non-U.S. Corporate Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		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
Real Estate [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[3]	12	9
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	9
Mortgage Backed Securities [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		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
Other Fixed Income [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		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
Cash Equivalents [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		48	1
Cash Equivalents [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		48	1
Insurance Contracts [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[4]	5	16
Insurance Contracts [Member] | Significant Observable Inputs (Level 2) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[4]	5	$ 16
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.