Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Jun. 30, 2022	Sep. 30, 2021	Jun. 30, 2021
Regulatory Assets
Regulatory assets	$ 371	$ 397	$ 396
Regulatory Liabilities
Regulatory liabilities	336	388	334
Postretirement benefit overcollections
Regulatory Liabilities
Regulatory liabilities	12	13	12
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	1	36	21
State tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	34	32	30
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	281	287	269
Other
Regulatory Liabilities
Regulatory liabilities	8	20	2
Income taxes recoverable
Regulatory Assets
Regulatory assets	151	143	131
Underfunded pension and postretirement plans
Regulatory Assets
Regulatory assets	103	108	166
Environmental costs
Regulatory Assets
Regulatory assets	34	58	58
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	14	11	0
Removal costs, net
Regulatory Assets
Regulatory assets	22	24	24
Other
Regulatory Assets
Regulatory assets	$ 47	$ 53	$ 17