Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Jun. 30, 2025	Sep. 30, 2024	Jun. 30, 2024
Regulatory Assets
Regulatory assets	$ 319	$ 319	$ 311
Regulatory Liabilities
Regulatory liabilities	323	329	341
Postretirement benefits
Regulatory Liabilities
Regulatory liabilities	12	13	11
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	10	17	33
State income tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	45	44	44
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	243	247	248
Other
Regulatory Liabilities
Regulatory liabilities	13	8	5
Income taxes recoverable
Regulatory Assets
Regulatory assets	111	105	91
Underfunded pension plans
Regulatory Assets
Regulatory assets	102	106	109
Environmental costs
Regulatory Assets
Regulatory assets	27	28	28
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	15	0	0
Removal costs, net
Regulatory Assets
Regulatory assets	29	28	26
Other
Regulatory Assets
Regulatory assets	$ 35	$ 52	$ 57

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