Commitments and Contingencies - Schedule of Loss Contingencies by Contingency (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2024	Sep. 30, 2023
Loss Contingencies [Line Items]
Reserve for environmental liabilities, current	$ 28	$ 31
Reserve for environmental liabilities, noncurrent	194	211
Total reserves for environmental liabilities	222	242
Total asbestos-related liabilities	416	422
Total asbestos-related assets	330	301
Net asbestos-related liabilities	86	121
Restricted
Insurance receivables for asbestos-related liabilities	49	50
Total self-insured liabilities	339	333
Insurance receivables, current	6	6
Insurance receivables, noncurrent	14	14
Total insurance receivables	20	20
Asbestos Issue
Loss Contingencies [Line Items]
Total asbestos-related assets	281	251
Restricted
Cash	14	20
Investments	267	231
Other current liabilities
Loss Contingencies [Line Items]
Total asbestos-related liabilities	58	58
Restricted
Total self-insured liabilities	90	86
Other noncurrent liabilities
Loss Contingencies [Line Items]
Total asbestos-related liabilities	358	364
Restricted
Total self-insured liabilities	226	226
Other current assets
Loss Contingencies [Line Items]
Total asbestos-related assets	22	28
Other noncurrent assets
Loss Contingencies [Line Items]
Total asbestos-related assets	308	273
Accrued compensation and benefits
Restricted
Total self-insured liabilities	$ 23	$ 21