Retirement Plans - Plan Assets by Asset Category (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Pension Plan | United States
Retirement Plans [Line Items]
Fair value of plan assets	$ 1,499	$ 1,730	$ 2,459
Pension Plan | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	1,388	1,433	2,344
Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets	144	144	$ 172
Postretirement Benefits | Cash and Cash Equivalents
Retirement Plans [Line Items]
Fair value of plan assets	8	13
Postretirement Benefits | Large-Cap
Retirement Plans [Line Items]
Fair value of plan assets	71	66
Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets		65
Postretirement Benefits | Total Investments in the Fair Value Hierarchy
Retirement Plans [Line Items]
Fair value of plan assets	65
Postretirement Benefits | Total Investments in the Fair Value Hierarchy | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets		79
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | United States
Retirement Plans [Line Items]
Fair value of plan assets	1,333	1,574
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	1,298	1,336
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	61	40
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	52	150
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Large-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	60	160
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Large-Cap | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	52	45
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Small-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	65	175
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | International - Developed | United States
Retirement Plans [Line Items]
Fair value of plan assets	108	139
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | International - Developed | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	52	43
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | International - Emerging | United States
Retirement Plans [Line Items]
Fair value of plan assets	20	39
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | International - Emerging | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	2	3
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Government | United States
Retirement Plans [Line Items]
Fair value of plan assets	225	217
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Government | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	701	650
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Corporate/Other | United States
Retirement Plans [Line Items]
Fair value of plan assets	583	804
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Corporate/Other | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	415	418
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Alternative | United States
Retirement Plans [Line Items]
Fair value of plan assets	211
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Real Estate | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	9	9
Fair Value, Inputs, Level 1, 2 and 3 | Pension Plan | Hedge Fund | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	15	18
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	1,061	1,533
Quoted Prices in Active Markets (Level 1) | Pension Plan | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	393	506
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	52	150
Quoted Prices in Active Markets (Level 1) | Pension Plan | Large-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	60	160
Quoted Prices in Active Markets (Level 1) | Pension Plan | Large-Cap | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	9	8
Quoted Prices in Active Markets (Level 1) | Pension Plan | Small-Cap | United States
Retirement Plans [Line Items]
Fair value of plan assets	65	175
Quoted Prices in Active Markets (Level 1) | Pension Plan | International - Developed | United States
Retirement Plans [Line Items]
Fair value of plan assets	108	139
Quoted Prices in Active Markets (Level 1) | Pension Plan | International - Developed | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	12	12
Quoted Prices in Active Markets (Level 1) | Pension Plan | International - Emerging | United States
Retirement Plans [Line Items]
Fair value of plan assets	20	39
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	225	216
Quoted Prices in Active Markets (Level 1) | Pension Plan | Government | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	40	50
Quoted Prices in Active Markets (Level 1) | Pension Plan | Corporate/Other | United States
Retirement Plans [Line Items]
Fair value of plan assets	583	804
Quoted Prices in Active Markets (Level 1) | Pension Plan | Corporate/Other | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	271	277
Quoted Prices in Active Markets (Level 1) | Pension Plan | Alternative | United States
Retirement Plans [Line Items]
Fair value of plan assets	0
Quoted Prices in Active Markets (Level 1) | Pension Plan | Real Estate | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	9	9
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
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	8
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Cash and Cash Equivalents
Retirement Plans [Line Items]
Fair value of plan assets	8	13
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 | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Total Investments in the Fair Value Hierarchy
Retirement Plans [Line Items]
Fair value of plan assets
Quoted Prices in Active Markets (Level 1) | Postretirement Benefits | Total Investments in the Fair Value Hierarchy | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets		13
Significant Other Observable Inputs (Level 2) | Pension Plan | United States
Retirement Plans [Line Items]
Fair value of plan assets	272	41
Significant Other Observable Inputs (Level 2) | Pension Plan | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	905	830
Significant Other Observable Inputs (Level 2) | Pension Plan | Cash and Cash Equivalents | United States
Retirement Plans [Line Items]
Fair value of plan assets	61	40
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	43	37
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	40	31
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	2	3
Significant Other Observable Inputs (Level 2) | Pension Plan | Government | United States
Retirement Plans [Line Items]
Fair value of plan assets	0	1
Significant Other Observable Inputs (Level 2) | Pension Plan | Government | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	661	600
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	144	141
Significant Other Observable Inputs (Level 2) | Pension Plan | Alternative | United States
Retirement Plans [Line Items]
Fair value of plan assets	211
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	15	18
Significant Other Observable Inputs (Level 2) | Postretirement Benefits
Retirement Plans [Line Items]
Fair value of plan assets
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	71
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	71	66
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Total Investments in the Fair Value Hierarchy
Retirement Plans [Line Items]
Fair value of plan assets
Significant Other Observable Inputs (Level 2) | Postretirement Benefits | Total Investments in the Fair Value Hierarchy | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets		66
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 | Alternative | United States
Retirement Plans [Line Items]
Fair value of plan assets	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
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 | Real Estate
Retirement Plans [Line Items]
Fair value of plan assets
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Total Investments in the Fair Value Hierarchy
Retirement Plans [Line Items]
Fair value of plan assets
Significant Unobservable Inputs (Level 3) | Postretirement Benefits | Total Investments in the Fair Value Hierarchy | Foreign Plan
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	295	322
Real Estate Investments Measured at Net Asset Value | Pension Plan | Real Estate | Foreign Plan
Retirement Plans [Line Items]
Fair value of plan assets	90	97
Real Estate Investments Measured at Net Asset Value | Pension Plan | Due to Broker | United States
Retirement Plans [Line Items]
Fair value of plan assets	$ (129)	$ (166)