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Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Derivative Instruments That Do Not Receive Hedge Accounting Treatment (Details)	12 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2021 USD ($)
Derivative
Change in Unrealized gains (losses) on Interest Rate Derivatives	$ (728,000,000)	$ (402,000,000)
Interest rate swaps	905,000,000	1,639,000,000
Unrealized gains/losses on derivatives	0
Interest Rate Swap
Derivative
Fair value	(233,000,000)	(455,000,000)
Commodity Contract Derivatives
Derivative
Fair value	$ 145,000,000	$ 247,000,000
Natural Gas Contract Derivatives
Derivative
Number of contracts	44	40
Notional amount	296,000,000	263,000,000
Fair value	$ 145,000,000	$ 247,000,000
Commodity Contract under FHP
Derivative
Number of contracts	225	0
Notional amount	256
Fair value	$ 115,000,000	$ 0
Accounts payable and accrued liabilities
Derivative
Fair value	12,000,000	7,000,000
Interest rate swaps	54,000,000	115,000,000
Accounts payable and accrued liabilities | Interest Rate Swap
Derivative
Fair value	(3,000,000)	(22,000,000)
Accounts payable and accrued liabilities | Commodity Contract Derivatives
Derivative
Fair value		(3,000,000)
Accounts payable and accrued liabilities | Commodity Contract under FHP
Derivative
Fair value	(8,000,000)
Other Regulatory Assets (Liabilities) | Interest Rate Swap
Derivative
Unrealized gains/losses on derivatives	(103,000,000)	(115,000,000)
Other Regulatory Assets (Liabilities) | Commodity Contract under FHP
Derivative
Unrealized gains/losses on derivatives	$ 47,000,000	$ 0

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of interest rate derivatives held at each balance sheet date.

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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

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Number of price risk derivative instruments held by the entity at the reporting date.

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