Plan Assets by Asset Category (Details) - USD ($) $ in Millions	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
U.S. Pension Plans
Retirement Plans [Line Items]
Fair value of plan assets	$ 3,293	$ 2,606	$ 2,504
U.S. Pension Plans | Cash
Retirement Plans [Line Items]
Fair value of plan assets	38	75
U.S. Pension Plans | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	692	500
U.S. Pension Plans | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets	267	235
U.S. Pension Plans | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets	655	472
U.S. Pension Plans | Government
Retirement Plans [Line Items]
Fair value of plan assets	345	248
U.S. Pension Plans | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets	950	753
U.S. Pension Plans | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	346	323
Non-U.S. Pension
Retirement Plans [Line Items]
Fair value of plan assets	2,536	1,177	1,201
Non-U.S. Pension | Cash
Retirement Plans [Line Items]
Fair value of plan assets	90	98
Non-U.S. Pension | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	317	68
Non-U.S. Pension | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets	453	104
Non-U.S. Pension | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets	19	16
Non-U.S. Pension | Government
Retirement Plans [Line Items]
Fair value of plan assets	864	441
Non-U.S. Pension | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets	561	220
Non-U.S. Pension | Hedge Funds
Retirement Plans [Line Items]
Fair value of plan assets	169	172
Non-U.S. Pension | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	63	58
Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets	196	194	219
Postretirement Benefits | Cash
Retirement Plans [Line Items]
Fair value of plan assets	7	10
Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	31	30
Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets	10	10
Postretirement Benefits | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets	23	22
Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets	12	10
Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets	23	22
Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets	65	67
Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets	12	12
Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	13	11
Quoted Prices in Active Markets (Level 1) | U.S. Pension Plans
Retirement Plans [Line Items]
Fair value of plan assets	2,268	2,114
Quoted Prices in Active Markets (Level 1) | U.S. Pension Plans | Cash
Retirement Plans [Line Items]
Fair value of plan assets	38	75
Quoted Prices in Active Markets (Level 1) | U.S. Pension Plans | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	499	500
Quoted Prices in Active Markets (Level 1) | U.S. Pension Plans | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets	252	235
Quoted Prices in Active Markets (Level 1) | U.S. Pension Plans | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets	566	472
Quoted Prices in Active Markets (Level 1) | U.S. Pension Plans | Government
Retirement Plans [Line Items]
Fair value of plan assets	280	217
Quoted Prices in Active Markets (Level 1) | U.S. Pension Plans | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets	633	615
Quoted Prices in Active Markets (Level 1) | U.S. Pension Plans | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets (Level 1) | Non-U.S. Pension
Retirement Plans [Line Items]
Fair value of plan assets	1,269	804
Quoted Prices in Active Markets (Level 1) | Non-U.S. Pension | Cash
Retirement Plans [Line Items]
Fair value of plan assets	90	98
Quoted Prices in Active Markets (Level 1) | Non-U.S. Pension | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	152	68
Quoted Prices in Active Markets (Level 1) | Non-U.S. Pension | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets	160	104
Quoted Prices in Active Markets (Level 1) | Non-U.S. Pension | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets	19	16
Quoted Prices in Active Markets (Level 1) | Non-U.S. Pension | Government
Retirement Plans [Line Items]
Fair value of plan assets	452	319
Quoted Prices in Active Markets (Level 1) | Non-U.S. Pension | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets	385	192
Quoted Prices in Active Markets (Level 1) | Non-U.S. Pension | Hedge Funds
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets (Level 1) | Non-U.S. Pension | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	11	7
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets	196	194
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Cash
Retirement Plans [Line Items]
Fair value of plan assets	7	10
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	31	30
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets	10	10
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets	23	22
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets	12	10
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets	23	22
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets	65	67
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets	12	12
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	13	11
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans
Retirement Plans [Line Items]
Fair value of plan assets	679	169
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Cash
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	193	0
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets	15	0
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets	89	0
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Government
Retirement Plans [Line Items]
Fair value of plan assets	65	31
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets	317	138
Significant Other Observable Inputs (Level 2) | U.S. Pension Plans | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension
Retirement Plans [Line Items]
Fair value of plan assets	1,215	322
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Cash
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	165	0
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets	293	0
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Government
Retirement Plans [Line Items]
Fair value of plan assets	412	122
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets	176	28
Significant Other Observable Inputs (Level 2) | Non-U.S. Pension | Hedge Funds
Retirement Plans [Line Items]
Fair value of plan assets	169	172
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	0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Cash
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | International-Developed
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | U.S. Pension Plans
Retirement Plans [Line Items]
Fair value of plan assets	346	323	335
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 | 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 | Hedge Funds
Retirement Plans [Line Items]
Fair value of plan assets	0	0	4
Fair Value, Inputs, Level 3 | U.S. Pension Plans | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	346	323	331
Fair Value, Inputs, Level 3 | Non-U.S. Pension
Retirement Plans [Line Items]
Fair value of plan assets	52	51	20
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 | 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	0
Fair Value, Inputs, Level 3 | Non-U.S. Pension | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets	52	51	$ 20
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