Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022	Mar. 31, 2022
Regulatory Assets
Regulatory assets	$ 359	$ 340	$ 384
Regulatory Liabilities
Regulatory liabilities	345	335	360
Postretirement benefit overcollections
Regulatory Liabilities
Regulatory liabilities	10	11	12
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	28	3	17
State tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	39	38	34
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	262	279	283
Other
Regulatory Liabilities
Regulatory liabilities	6	4	14
Income taxes recoverable
Regulatory Assets
Regulatory assets	94	83	148
Underfunded pension plans
Regulatory Assets
Regulatory assets	118	114	104
Environmental costs
Regulatory Assets
Regulatory assets	34	37	55
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	38	32	6
Removal costs, net
Regulatory Assets
Regulatory assets	22	22	22
Other
Regulatory Assets
Regulatory assets	$ 53	$ 52	$ 49