Plan Assets by Asset Category (Details) - USD ($) $ in Millions		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
U.S. Pension Plans
Retirement Plans [Line Items]
Fair value of plan assets		$ 2,890		$ 2,606
Defined Benefit Plan, Total Plan Assets		3,165	$ 3,293
U.S. Pension Plans | Cash
Retirement Plans [Line Items]
Fair value of plan assets		70	38
U.S. Pension Plans | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		652	692
U.S. Pension Plans | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		281	267
U.S. Pension Plans | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		649	655
U.S. Pension Plans | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		51
U.S. Pension Plans | Government
Retirement Plans [Line Items]
Fair value of plan assets		270	345
U.S. Pension Plans | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		917	950
U.S. Pension Plans | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets			2,947
Defined Benefit Plan, Investment Funds Measured At Net Asset Value	[1]	275	346
Non-U.S. Pension
Retirement Plans [Line Items]
Fair value of plan assets		2,152	2,484	1,177
Defined Benefit Plan, Total Plan Assets		2,181	2,536
Non-U.S. Pension | Cash
Retirement Plans [Line Items]
Fair value of plan assets		55	90
Non-U.S. Pension | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		242	317
Non-U.S. Pension | Mid Cap [Member]
Retirement Plans [Line Items]
Fair value of plan assets		2
Non-U.S. Pension | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		517	453
Non-U.S. Pension | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		13	19
Non-U.S. Pension | Government
Retirement Plans [Line Items]
Fair value of plan assets		618	864
Non-U.S. Pension | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		569	561
Non-U.S. Pension | Hedge Funds
Retirement Plans [Line Items]
Fair value of plan assets		112	169
Non-U.S. Pension | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		24	11
Defined Benefit Plan, Investment Funds Measured At Net Asset Value	[1]	29	52
Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets		177	196	$ 194
Defined Benefit Plan, Total Plan Assets		177	196
Postretirement Benefits | Cash
Retirement Plans [Line Items]
Fair value of plan assets		3	7
Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		28	31
Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		9	10
Postretirement Benefits | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		21	23
Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		11	12
Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets		21	23
Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		59	65
Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets		15	12
Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		10	13
Fair Value, Inputs, Level 1 | U.S. Pension Plans
Retirement Plans [Line Items]
Fair value of plan assets		2,345
Fair Value, Inputs, Level 1 | U.S. Pension Plans | Cash
Retirement Plans [Line Items]
Fair value of plan assets		2	38
Fair Value, Inputs, Level 1 | U.S. Pension Plans | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		375	499
Fair Value, Inputs, Level 1 | U.S. Pension Plans | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		281	252
Fair Value, Inputs, Level 1 | U.S. Pension Plans | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		569	566
Fair Value, Inputs, Level 1 | U.S. Pension Plans | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		24
Fair Value, Inputs, Level 1 | U.S. Pension Plans | Government
Retirement Plans [Line Items]
Fair value of plan assets		243	280
Fair Value, Inputs, Level 1 | U.S. Pension Plans | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		851	633
Fair Value, Inputs, Level 1 | U.S. Pension Plans | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets			2,268
Fair Value, Inputs, Level 1 | Non-U.S. Pension
Retirement Plans [Line Items]
Fair value of plan assets		513	608
Fair Value, Inputs, Level 1 | Non-U.S. Pension | Cash
Retirement Plans [Line Items]
Fair value of plan assets		45	59
Fair Value, Inputs, Level 1 | Non-U.S. Pension | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		18	22
Fair Value, Inputs, Level 1 | Non-U.S. Pension | Mid Cap [Member]
Retirement Plans [Line Items]
Fair value of plan assets		2
Fair Value, Inputs, Level 1 | Non-U.S. Pension | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		58	52
Fair Value, Inputs, Level 1 | Non-U.S. Pension | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Non-U.S. Pension | Government
Retirement Plans [Line Items]
Fair value of plan assets		74	164
Fair Value, Inputs, Level 1 | Non-U.S. Pension | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		292	300
Fair Value, Inputs, Level 1 | Non-U.S. Pension | Hedge Funds
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Non-U.S. Pension | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		24	11
Fair Value, Inputs, Level 1 | Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Postretirement Benefits | Cash
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Postretirement Benefits | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 1 | Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans
Retirement Plans [Line Items]
Fair value of plan assets		545
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Cash
Retirement Plans [Line Items]
Fair value of plan assets		68	0
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		277	193
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0	15
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		80	89
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		27
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Government
Retirement Plans [Line Items]
Fair value of plan assets		27	65
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		66	317
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets			679
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension
Retirement Plans [Line Items]
Fair value of plan assets		1,639	1,876
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Cash
Retirement Plans [Line Items]
Fair value of plan assets		10	31
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		224	295
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Mid Cap [Member]
Retirement Plans [Line Items]
Fair value of plan assets		0
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		459	401
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		13	19
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Government
Retirement Plans [Line Items]
Fair value of plan assets		544	700
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		277	261
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Hedge Funds
Retirement Plans [Line Items]
Fair value of plan assets		112	169
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets		177	196
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Cash
Retirement Plans [Line Items]
Fair value of plan assets		3	7
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		28	31
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		9	10
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		21	23
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		11	12
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets		21	23
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		59	65
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets		15	12
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		10	13
Fair Value, Inputs, Level 3 | U.S. Pension Plans
Retirement Plans [Line Items]
Fair value of plan assets		0
Fair Value, Inputs, Level 3 | U.S. Pension Plans | Cash
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | U.S. Pension Plans | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | U.S. Pension Plans | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | U.S. Pension Plans | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | U.S. Pension Plans | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		0
Fair Value, Inputs, Level 3 | U.S. Pension Plans | Government
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | U.S. Pension Plans | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | U.S. Pension Plans | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets			0
Fair Value, Inputs, Level 3 | Non-U.S. Pension
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | Cash
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | Mid Cap [Member]
Retirement Plans [Line Items]
Fair value of plan assets		0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | Government
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | Hedge Funds
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits | Cash
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 3 | Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		$ 0	$ 0

[1] * The fair value of certain investments in real estate do not have a readily determinable fair value and requires the fund managers to independently arrive at fair value by calculating net asset value ("NAV") per share. In order to calculate NAV per share, the fund managers value the real estate investments using any one, or a combination of, the following methods: independent third party appraisals, discounted cash flow analysis of net cash flows projected to be generated by the investment and recent sales of comparable investments. Assumptions used to revalue the properties are updated every quarter. Due to the fact that the fund managers calculate NAV per share, the Company utilizes a practical expedient for measuring the fair value of its real-estate investments, as provided for under ASC 820, "Fair Value Measurement." In applying the practical expedient, the Company is not required to further adjust the NAV provided by the fund manager in order to determine the fair value of its investment as the NAV per share is calculated in a manner consistent with the measurement principles of ASC 946, "Financial Services - Investment Companies," and as of the Company's measurement date. The Company believes this is an appropriate methodology to obtain the fair value of these assets. For the component of the real estate portfolio under development, the investments are carried at cost until they are completed and valued by a third party appraiser. In accordance with ASU No. 2015-07, "Disclosures for Investments in Certain Entities That Calculate Net Asset Value per Share (or Its Equivalent)," investments for which fair value is measured using the net asset value per share practical expedient should be disclosed separate from the fair value hierarchy. The fair value amounts presented in this table are intended to permit reconciliation of total plan assets to the amounts presented in the notes to consolidated financial statements.