Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Mar. 31, 2025	Sep. 30, 2024	Mar. 31, 2024
Regulatory Assets
Regulatory assets	$ 312	$ 319	$ 312
Regulatory Liabilities
Regulatory liabilities	356	329	347
Postretirement benefits
Regulatory Liabilities
Regulatory liabilities	12	13	11
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	37	17	34
State income tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	45	44	44
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	246	247	250
Other
Regulatory Liabilities
Regulatory liabilities	16	8	8
Income taxes recoverable
Regulatory Assets
Regulatory assets	109	105	93
Underfunded pension plans
Regulatory Assets
Regulatory assets	104	106	109
Environmental costs
Regulatory Assets
Regulatory assets	25	28	32
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	4	0	0
Removal costs, net
Regulatory Assets
Regulatory assets	29	28	23
Other
Regulatory Assets
Regulatory assets	$ 41	$ 52	$ 55

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