Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Mar. 31, 2024	Sep. 30, 2023	Mar. 31, 2023
Regulatory Assets
Regulatory assets	$ 312	$ 347	$ 359
Regulatory Liabilities
Regulatory liabilities	347	366	345
Postretirement benefit overcollections
Regulatory Liabilities
Regulatory liabilities	11	12	10
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	34	55	28
State tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	44	43	39
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	250	254	262
Other
Regulatory Liabilities
Regulatory liabilities	8	2	6
Income taxes recoverable
Regulatory Assets
Regulatory assets	93	94	94
Underfunded pension plans
Regulatory Assets
Regulatory assets	109	111	118
Environmental costs
Regulatory Assets
Regulatory assets	32	28	34
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	0	27	38
Removal costs, net
Regulatory Assets
Regulatory assets	23	23	22
Other
Regulatory Assets
Regulatory assets	$ 55	$ 64	$ 53