Utility Regulatory Assets and Liabilities and Regulatory Matters - Regulatory Assets and Liabilities Associated with Utilities (Details) - Utilities - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Regulatory Assets [Line Items]
Regulatory assets	$ 347	$ 340
Regulatory Liabilities [Line Items]
Regulatory liabilities	366	335
Postretirement benefits
Regulatory Liabilities [Line Items]
Regulatory liabilities	12	11
Deferred fuel and power refunds
Regulatory Liabilities [Line Items]
Regulatory liabilities	55	3
State income tax benefits — distribution system repairs
Regulatory Liabilities [Line Items]
Regulatory liabilities	43	38
Excess federal deferred income taxes
Regulatory Liabilities [Line Items]
Regulatory liabilities	254	279
Other
Regulatory Liabilities [Line Items]
Regulatory liabilities	2	4
Income taxes recoverable
Regulatory Assets [Line Items]
Regulatory assets	94	83
Underfunded pension plans
Regulatory Assets [Line Items]
Regulatory assets	111	114
Environmental costs
Regulatory Assets [Line Items]
Regulatory assets	28	37
Deferred fuel and power costs
Regulatory Assets [Line Items]
Regulatory assets	27	32
Removal costs, net
Regulatory Assets [Line Items]
Regulatory assets	23	22
Other
Regulatory Assets [Line Items]
Regulatory assets	$ 64	$ 52