Benefit Plans - Fair Value Measurements of Foreign Plan Assets (Detail) - Pension Plans - USD ($) $ in Millions	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,642	$ 1,932	$ 1,855
Foreign Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	821	678
Foreign Plans | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	28	14
Foreign Plans | Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	5
Foreign Plans | Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	150	127
Foreign Plans | Other fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	96	64
Foreign Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	314	256
Foreign Plans | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	28
Foreign Plans | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30	26
Foreign Plans | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	114	98
Foreign Plans | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	74	62
Foreign Plans | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	546	459
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	14	0
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	3	1
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	104	83
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	57
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	299	242
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	9	28
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	55	47
Foreign Plans | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	146	108
Foreign Plans | Significant Other Observable Inputs (Level 2) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	13
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	46	45
Foreign Plans | Significant Other Observable Inputs (Level 2) | Other fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33	7
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	26
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	20	15
Foreign Plans | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	114	98
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	114	98	$ 102
Foreign Plans | Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value [Member] | Foreign Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15	13
Net Asset Value [Member] | Foreign Plans | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value [Member] | Foreign Plans | Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value [Member] | Foreign Plans | Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value [Member] | Foreign Plans | Other fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value [Member] | Foreign Plans | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15	13
Net Asset Value [Member] | Foreign Plans | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value [Member] | Foreign Plans | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value [Member] | Foreign Plans | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Net Asset Value [Member] | Foreign Plans | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0