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Risk Management Activities and Derivative Transactions Derivatives Under FTP (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2022	Sep. 30, 2021
Derivative
Forward Contract Derivative Asset, at Fair Value	$ 2	$ 2
Natural Gas Contract Derivatives
Derivative
Fair value	202	247
Commodity Contract under FHP
Derivative
Fair value	52	0
Amount recognized for unrealized gains (losses)	52	0
Fair Value, Inputs, Level 2
Derivative
Forward Contract Derivative Asset, at Fair Value	2	$ 2
Fair Value, Inputs, Level 2 | Commodity Contract under FHP
Derivative
Fair value	$ 52

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- Definition

Fair value as of the balance sheet date of forward contract derivative assets.

+ References

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=123594938&loc=d3e13433-108611

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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 derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3602-108585

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