Retirement Plans - Plan Assets by Asset Category (Details) - USD ($) $ in Millions	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Pension Plan | United States
Retirement Plans [Line Items]
Fair value of plan assets	$ 1,730	$ 2,459	$ 2,706
Pension Plan | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	1,433	2,344	2,213
Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets	144	172	$ 153
Postretirement Benefits | Cash and Cash Equivalents
Retirement Plans [Line Items]
Fair value of plan assets	13	5
Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	66	24
Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		8
Postretirement Benefits | International - Developed
Retirement Plans [Line Items]
Fair value of plan assets		19
Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		12
Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets		20
Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		56
Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		11
Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets	65	17
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | United States
Retirement Plans [Line Items]
Fair value of plan assets	1,574	2,256
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	1,336	2,239
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Cash and Cash Equivalents | United States
Retirement Plans [Line Items]
Fair value of plan assets	40	75
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Cash and Cash Equivalents | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	150	151
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Large-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	160	185
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Large-Cap | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	45	197
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Small-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	175	215
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | International - Developed | United States
Retirement Plans [Line Items]
Fair value of plan assets	139	182
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | International - Developed | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	43	128
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | International - Emerging | United States
Retirement Plans [Line Items]
Fair value of plan assets	39	34
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | International - Emerging | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	3	2
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Government | United States
Retirement Plans [Line Items]
Fair value of plan assets	217	286
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Government | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	650	1,123
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Corporate/Other | United States
Retirement Plans [Line Items]
Fair value of plan assets	804	1,279
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Corporate/Other | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	418	597
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Real Estate | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	9	14
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Hedge Fund | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	18	27
Fair Value, Inputs, Level 1, 2 and 3 | Postretirement Benefits | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	79
Quoted Prices in Active Markets (Level 1) | Pension Plan | United States
Retirement Plans [Line Items]
Fair value of plan assets	1,533	1,993
Quoted Prices in Active Markets (Level 1) | Pension Plan | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	506	615
Quoted Prices in Active Markets (Level 1) | Pension Plan | Cash and Cash Equivalents | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets (Level 1) | Pension Plan | Cash and Cash Equivalents | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	150	151
Quoted Prices in Active Markets (Level 1) | Pension Plan | Large-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	160	185
Quoted Prices in Active Markets (Level 1) | Pension Plan | Large-Cap | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	8	23
Quoted Prices in Active Markets (Level 1) | Pension Plan | Small-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	175	215
Quoted Prices in Active Markets (Level 1) | Pension Plan | International - Developed | United States
Retirement Plans [Line Items]
Fair value of plan assets	139	182
Quoted Prices in Active Markets (Level 1) | Pension Plan | International - Developed | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	12	30
Quoted Prices in Active Markets (Level 1) | Pension Plan | International - Emerging | United States
Retirement Plans [Line Items]
Fair value of plan assets	39	34
Quoted Prices in Active Markets (Level 1) | Pension Plan | International - Emerging | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets (Level 1) | Pension Plan | Government | United States
Retirement Plans [Line Items]
Fair value of plan assets	216	98
Quoted Prices in Active Markets (Level 1) | Pension Plan | Government | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	50	77
Quoted Prices in Active Markets (Level 1) | Pension Plan | Corporate/Other | United States
Retirement Plans [Line Items]
Fair value of plan assets	804	1,279
Quoted Prices in Active Markets (Level 1) | Pension Plan | Corporate/Other | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	277	320
Quoted Prices in Active Markets (Level 1) | Pension Plan | Real Estate | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	9	14
Quoted Prices in Active Markets (Level 1) | Pension Plan | Hedge Fund | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets		5
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	13
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Cash and Cash Equivalents
Retirement Plans [Line Items]
Fair value of plan assets	13	5
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | International - Developed
Retirement Plans [Line Items]
Fair value of plan assets		0
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		0
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets		0
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		0
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		0
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets		0
Significant Other Observable Inputs (Level 2) | Pension Plan | United States
Retirement Plans [Line Items]
Fair value of plan assets	41	263
Significant Other Observable Inputs (Level 2) | Pension Plan | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	830	1,624
Significant Other Observable Inputs (Level 2) | Pension Plan | Cash and Cash Equivalents | United States
Retirement Plans [Line Items]
Fair value of plan assets	40	75
Significant Other Observable Inputs (Level 2) | Pension Plan | Cash and Cash Equivalents | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension Plan | Large-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension Plan | Large-Cap | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	37	174
Significant Other Observable Inputs (Level 2) | Pension Plan | Small-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension Plan | International - Developed | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension Plan | International - Developed | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	31	98
Significant Other Observable Inputs (Level 2) | Pension Plan | International - Emerging | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension Plan | International - Emerging | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	3	2
Significant Other Observable Inputs (Level 2) | Pension Plan | Government | United States
Retirement Plans [Line Items]
Fair value of plan assets	1	188
Significant Other Observable Inputs (Level 2) | Pension Plan | Government | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	600	1,046
Significant Other Observable Inputs (Level 2) | Pension Plan | Corporate/Other | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension Plan | Corporate/Other | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	141	277
Significant Other Observable Inputs (Level 2) | Pension Plan | Real Estate | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Other Observable Inputs (Level 2) | Pension Plan | Hedge Fund | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	18	27
Significant Other Observable Inputs (Level 2) | Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets		167
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	66
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Cash and Cash Equivalents
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	66	24
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		8
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | International - Developed
Retirement Plans [Line Items]
Fair value of plan assets		19
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		12
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets		20
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		56
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		11
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets		17
Significant Unobservable Inputs (Level 3) | Pension Plan | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Cash and Cash Equivalents | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Cash and Cash Equivalents | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Large-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Large-Cap | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Small-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | International - Developed | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | International - Developed | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | International - Emerging | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | International - Emerging | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Government | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Government | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Corporate/Other | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Corporate/Other | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Real Estate | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Pension Plan | Hedge Fund | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets		0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Cash and Cash Equivalents
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	0	0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Small-Cap
Retirement Plans [Line Items]
Fair value of plan assets		0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | International - Developed
Retirement Plans [Line Items]
Fair value of plan assets		0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | International - Emerging
Retirement Plans [Line Items]
Fair value of plan assets		0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Government
Retirement Plans [Line Items]
Fair value of plan assets		0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Corporate/Other
Retirement Plans [Line Items]
Fair value of plan assets		0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		0
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Commodities
Retirement Plans [Line Items]
Fair value of plan assets		0
Real Estate Investments Measured at Net Asset Value | Pension Plan | Real Estate | United States
Retirement Plans [Line Items]
Fair value of plan assets	322	280
Real Estate Investments Measured at Net Asset Value | Pension Plan | Real Estate | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	97	105
Real Estate Investments Measured at Net Asset Value | Pension Plan | Due to Broker | United States
Retirement Plans [Line Items]
Fair value of plan assets	$ (166)	$ (77)