Employee Benefit Plans - Fair Value of Pension Plan Assets by Asset Category (Detail) - USD ($) $ in Millions		Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		$ 474	$ 462
Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			18
Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		458	429
Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		15	14
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		158	158
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			18
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		157	139
Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		316	304
Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		301	290
Significant Observable Inputs (Level 2) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		15	14
Cash and Cash Equivalent Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
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		1	1
U.S. Equity Securities [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			18
U.S. Equity Securities [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			18
Equity Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	199	178
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]	75	59
Equity Funds [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	124	119
Fixed Income Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[2]	176	241
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]	8	79
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]	168	162
Real Estate [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[3]	9	9
Real Estate [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	[3]		1
Real Estate [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[3]	9	8
Cash Equivalent Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		74	1
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		74
Cash Equivalent Funds [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			1
Insurance Contracts [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[4]	15	14
Insurance Contracts [Member] | Significant Observable Inputs (Level 2) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[4]	$ 15	$ 14

[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.