Benefit Plans - Fair Value Measurements of Foreign Plan Assets (Detail) - Pension Plans - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,926	$ 2,642	$ 1,932
Foreign Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	859	821
Foreign Plans | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33	28
Foreign Plans | Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	6
Foreign Plans | Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	199	150
Foreign Plans | Other fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	100	96
Foreign Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	319	314
Foreign Plans | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	9
Foreign Plans | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30	30
Foreign Plans | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	113	114
Foreign Plans | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	53	74
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	549	546
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15	14
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	3
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	105	104
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63	63
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	305	299
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	9
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	52	55
Foreign Plans | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	182	146
Foreign Plans | Significant Other Observable Inputs (Level 2) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18	14
Foreign Plans | Significant Other Observable Inputs (Level 2) | Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3	3
Foreign Plans | Significant Other Observable Inputs (Level 2) | Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	94	46
Foreign Plans | Significant Other Observable Inputs (Level 2) | Other fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	37	33
Foreign Plans | Significant Other Observable Inputs (Level 2) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Other Observable Inputs (Level 2) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30	30
Foreign Plans | Significant Other Observable Inputs (Level 2) | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Other Observable Inputs (Level 2) | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	20
Foreign Plans | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	113	114
Foreign Plans | Significant Unobservable Inputs (Level 3) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Unobservable Inputs (Level 3) | Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Unobservable Inputs (Level 3) | Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Unobservable Inputs (Level 3) | Other fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Unobservable Inputs (Level 3) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Unobservable Inputs (Level 3) | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Foreign Plans | Significant Unobservable Inputs (Level 3) | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	113	114
Foreign Plans | Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value | Foreign Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	15
Net Asset Value | Foreign Plans | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value | Foreign Plans | Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value | Foreign Plans | Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value | Foreign Plans | Other fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value | Foreign Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	15
Net Asset Value | Foreign Plans | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value | Foreign Plans | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value | Foreign Plans | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value | Foreign Plans | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0