Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024	Dec. 31, 2023
Regulatory Assets
Regulatory assets	$ 313	$ 319	$ 328
Regulatory Liabilities
Regulatory liabilities	322	329	367
Postretirement benefits
Regulatory Liabilities
Regulatory liabilities	13	13	11
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	12	17	59
State income tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	45	44	43
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	245	247	252
Other
Regulatory Liabilities
Regulatory liabilities	7	8	2
Income taxes recoverable
Regulatory Assets
Regulatory assets	107	105	94
Underfunded pension plans
Regulatory Assets
Regulatory assets	105	106	110
Environmental costs
Regulatory Assets
Regulatory assets	26	28	26
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	0	0	17
Removal costs, net
Regulatory Assets
Regulatory assets	30	28	23
Other
Regulatory Assets
Regulatory assets	$ 45	$ 52	$ 58