Utility Regulatory Assets and Liabilities and Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - Utilities - USD ($) $ in Millions	Dec. 31, 2021	Sep. 30, 2021	Dec. 31, 2020
Regulatory Assets
Regulatory assets	$ 412	$ 397	$ 395
Regulatory Liabilities
Regulatory liabilities	346	388	346
Postretirement benefit overcollections
Regulatory Liabilities
Regulatory liabilities	13	13	13
Deferred fuel and power refunds
Regulatory Liabilities
Regulatory liabilities	1	36	24
State tax benefits — distribution system repairs
Regulatory Liabilities
Regulatory liabilities	33	32	28
Excess federal deferred income taxes
Regulatory Liabilities
Regulatory liabilities	285	287	272
Other
Regulatory Liabilities
Regulatory liabilities	14	20	9
Income taxes recoverable
Regulatory Assets
Regulatory assets	145	143	126
Underfunded pension and postretirement plans
Regulatory Assets
Regulatory assets	106	108	172
Environmental costs
Regulatory Assets
Regulatory assets	57	58	59
Deferred fuel and power costs
Regulatory Assets
Regulatory assets	29	11	0
Removal costs, net
Regulatory Assets
Regulatory assets	23	24	24
Other
Regulatory Assets
Regulatory assets	$ 52	$ 53	$ 14