Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Regulatory Assets
Regulatory assets	$ 328	$ 347	$ 393
Regulatory Liabilities
Regulatory liabilities	367	366	320
Postretirement benefit overcollections
Regulatory Liabilities
Regulatory liabilities	11	12	11
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	59	55	3
State tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	43	43	39
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	252	254	264
Other
Regulatory Liabilities
Regulatory liabilities	2	2	3
Income taxes recoverable
Regulatory Assets
Regulatory assets	94	94	93
Underfunded pension plans
Regulatory Assets
Regulatory assets	110	111	114
Environmental costs
Regulatory Assets
Regulatory assets	26	28	36
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	17	27	71
Removal costs, net
Regulatory Assets
Regulatory assets	23	23	25
Other
Regulatory Assets
Regulatory assets	$ 58	$ 64	$ 54