Regulatory Assets and Liabilities Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Regulatory Assets and Liabilities
Non-current regulatory liabilities	$ 141	$ 83
Current regulatory assets	127	191
Regulatory assets	8,047	9,408
Net unrealized gains (losses)	(12)	(64)
Regulatory Assets	8,174	9,599
Current regulatory liabilities	228	174
Regulatory asset amount expensed	63	71	$ 31
Regulatory Liabilities	369	257
Environmental Costs Recognized, Capitalized	308	215
Regulatory Asset
Regulatory Assets and Liabilities
Regulatory assets	168	154
Unrealized losses on interest rate derivatives
Regulatory Assets and Liabilities
Current regulatory assets	57	54
Regulatory assets	316	447
Non-nuclear decommissioning costs
Regulatory Assets and Liabilities
Regulatory assets	5,563	6,187
Pension Costs [Member]
Regulatory Assets and Liabilities
Regulatory assets	1,531	1,979
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Current regulatory assets	59	102
Regulatory assets	12	64
Deferred Fuel Costs [Member]
Regulatory Assets and Liabilities
Current regulatory assets	0	35
Nuclear decommissioning costs
Regulatory Assets and Liabilities
Regulatory assets	149	362
Other current assets
Regulatory Assets and Liabilities
Current regulatory assets	11	0
Unrealized gains/losses on commodity derivatives
Regulatory Assets and Liabilities
Non-current regulatory liabilities	10	2
Current regulatory liabilities	14	5
Deferred other post-retirement benefits cost
Regulatory Assets and Liabilities
Non-current regulatory liabilities	131	81
Fuel cost adjustment tax equivalents
Regulatory Assets and Liabilities
Current regulatory liabilities	203	169
Deferred Fuel Costs [Member]
Regulatory Assets and Liabilities
Current regulatory liabilities	$ 11	$ 0