Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Jun. 30, 2024	Sep. 30, 2023	Jun. 30, 2023
Regulatory Assets
Regulatory assets	$ 311	$ 347	$ 350
Regulatory Liabilities
Regulatory liabilities	341	366	376
Postretirement benefit overcollections
Regulatory Liabilities
Regulatory liabilities	11	12	10
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	33	55	63
State tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	44	43	40
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	248	254	260
Other
Regulatory Liabilities
Regulatory liabilities	5	2	3
Income taxes recoverable
Regulatory Assets
Regulatory assets	91	94	95
Underfunded pension plans
Regulatory Assets
Regulatory assets	109	111	118
Environmental costs
Regulatory Assets
Regulatory assets	28	28	28
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	0	27	30
Removal costs, net
Regulatory Assets
Regulatory assets	26	23	22
Other
Regulatory Assets
Regulatory assets	$ 57	$ 64	$ 57