Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Mar. 31, 2022	Sep. 30, 2021	Mar. 31, 2021
Regulatory Assets
Regulatory assets	$ 384	$ 397	$ 398
Regulatory Liabilities
Regulatory liabilities	360	388	335
Postretirement benefit overcollections
Regulatory Liabilities
Regulatory liabilities	12	13	12
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	17	36	17
State tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	34	32	29
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	283	287	270
Other
Regulatory Liabilities
Regulatory liabilities	14	20	7
Income taxes recoverable
Regulatory Assets
Regulatory assets	148	143	128
Underfunded pension and postretirement plans
Regulatory Assets
Regulatory assets	104	108	169
Environmental costs
Regulatory Assets
Regulatory assets	55	58	59
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	6	11	0
Removal costs, net
Regulatory Assets
Regulatory assets	22	24	24
Other
Regulatory Assets
Regulatory assets	$ 49	$ 53	$ 18