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Risk Management Activities and Derivative Transactions Derivatives Under FTP (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Derivative
Forward Contract Derivative Asset, at Fair Value	$ 11	$ 22
Coal Contract
Derivative
Fair value	(10)	(4)
Natural Gas Contract Derivatives
Derivative
Fair value	(20)	(37)
Fair Value, Inputs, Level 2
Derivative
Forward Contract Derivative Asset, at Fair Value	$ 11	$ 22

X

- Definition

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

+ References

No definition available.

+ Details

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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=121572278&loc=d3e13433-108611

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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