Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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Namespace Prefix:	tve_
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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

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13433-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 45

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 15

-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13495-108611

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Risk Management Activities and Derivative Transactions Derivatives Under Financial Trading Program (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012	Sep. 30, 2012
Natural Gas Futures
Derivative
Notional amount	0		0		0
Fair value	$ 0		$ 0		$ 0
Fuel Oil and Crude Oil Futures
Derivative
Notional amount	0		0		0
Fair value	0		0		0
Coal Futures
Derivative
Notional amount	0		0		0
Fair value	0		0		0
Natural Gas Swap
Derivative
Notional amount	195,127,500		195,127,500		294,462,500
Fair value	(164)		(164)		(232)
Fuel Oil and Crude Oil Swap
Derivative
Notional amount	1,184,000		1,184,000		1,390,000
Fair value	3		3		4
Coal Swap
Derivative
Notional amount	0		0		0
Fair value	0		0		0
Natural Gas Option
Derivative
Notional amount	0		0		0
Fair value	0		0		0
Fuel Oil and Crude Oil Option
Derivative
Notional amount	0		0		0
Fair value	0		0		0
Coal Option
Derivative
Notional amount	0		0		0
Fair value	0		0		0
Natural Gas Total Contracts
Derivative
Notional amount	195,127,500		195,127,500		294,462,500
Fair value	(164)		(164)		(232)
Decrease (increase) in fuel expense	(20)	(16)	(48)	(16)
Decrease (increase) in purchased power expense	(13)	(74)	(32)	(136)
Fuel Oil and Crude Oil Total Contracts
Derivative
Notional amount	1,184,000		1,184,000		1,390,000
Fair value	3		3		4
Decrease (increase) in fuel expense	0	2	2	7
Coal Contract Total Contracts
Derivative
Notional amount	0		0		0
Fair value	0		0		0
Decrease (increase) in fuel expense	0	0	(1)	1
Closed derivative contracts
Derivative
Fair value	$ (6)		$ (6)		$ (21)