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Risk Management Activities and Derivative Transactions Derivatives Under Financial Trading Program (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2014
Natural Gas Swap
Derivative
Fair value	[1]	$ (125)		$ (125)		$ (103)
Natural Gas Total Contracts
Derivative
Fair value		(125)		(125)		(103)
Decrease (increase) in fuel expense		(24)	$ (5)	(56)	$ (23)
Decrease (increase) in purchased power expense		(6)	(1)	(14)	(9)
Fuel Oil and Crude Oil Total Contracts
Derivative
Decrease (increase) in fuel expense		0	$ 0	1	$ 2
Coal Contract Total Contracts
Derivative
Fair value		0		0
Closed derivative contracts
Derivative
Fair value		$ (10)		$ (10)		$ (5)
[1] Fair value amounts presented are based on the net commodity position with the counterparty. Notional amounts disclosed represent the net absolute value of contractual amounts.

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- Definition

The decrease (increase) in fuel expense relating to the FTP.

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- Definition

The decrease (increase) in purchased power expense related to the FTP.

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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/presentationRef



-Publisher FASB



-Name Accounting Standards Codification



-Topic 815



-SubTopic 10



-Section 45



-Paragraph 6



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-Name Accounting Standards Codification



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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.

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