Benefit Plans - Fair Value Measurements of U.S. Plan Assets (Detail) - U.S. Plans - USD ($) $ in Millions	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1,157	$ 1,255
Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	192	150
Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	240	213
Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	78	153
Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	95	126
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	335	393
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	96	26
Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	123	193
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	401	483
Quoted Prices in Active Markets for Identical Assets (Level 1) | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	100	105
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	53	124
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	46	74
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	75	56
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	96	26
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	30	96
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	755	768
Significant Other Observable Inputs (Level 2) | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	192	150
Significant Other Observable Inputs (Level 2) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	139	108
Significant Other Observable Inputs (Level 2) | Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24	29
Significant Other Observable Inputs (Level 2) | Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	49	51
Significant Other Observable Inputs (Level 2) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	260	337
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	91	93
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	4
Significant Unobservable Inputs (Level 3) | Mortgage and asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Government and agency-U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Government and agency-Foreign
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2	$ 4	$ 12