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Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Mar. 31, 2015
Asset Retirement Obligations
Asset retirement obligations, period increase (decrease)	$ 54us-gaap_AssetRetirementObligationPeriodIncreaseDecrease
Decommissioning study update - ARO nuclear	5 years
Accretion expense	22us-gaap_AccretionExpense
Balance at September 30, 2014	3,169us-gaap_AssetRetirementObligation	[1]
Settlements (ash storage areas)	(21)us-gaap_AssetRetirementObligationLiabilitiesSettled	[1]
Accretion (recorded as regulatory asset)	75tve_AccretionRecordedAsRegulatoryAsset	[1]
Balance at March 31, 2015	3,223us-gaap_AssetRetirementObligation	[1]
Current portion of ARO	115us-gaap_AssetRetirementObligationCurrent
Nuclear
Asset Retirement Obligations
Balance at September 30, 2014	2,052us-gaap_AssetRetirementObligation / tve_ReconciliationOfAssetRetirementObligationLiabilityAxis = tve_NuclearMember	[1]
Settlements (ash storage areas)	0us-gaap_AssetRetirementObligationLiabilitiesSettled / tve_ReconciliationOfAssetRetirementObligationLiabilityAxis = tve_NuclearMember	[1]
Accretion (recorded as regulatory asset)	49tve_AccretionRecordedAsRegulatoryAsset / tve_ReconciliationOfAssetRetirementObligationLiabilityAxis = tve_NuclearMember	[1]
Balance at March 31, 2015	2,101us-gaap_AssetRetirementObligation / tve_ReconciliationOfAssetRetirementObligationLiabilityAxis = tve_NuclearMember	[1]
Non-nuclear
Asset Retirement Obligations
Balance at September 30, 2014	1,117us-gaap_AssetRetirementObligation / tve_ReconciliationOfAssetRetirementObligationLiabilityAxis = tve_NonNuclearMember	[1]
Settlements (ash storage areas)	(21)us-gaap_AssetRetirementObligationLiabilitiesSettled / tve_ReconciliationOfAssetRetirementObligationLiabilityAxis = tve_NonNuclearMember	[1]
Accretion (recorded as regulatory asset)	26tve_AccretionRecordedAsRegulatoryAsset / tve_ReconciliationOfAssetRetirementObligationLiabilityAxis = tve_NonNuclearMember	[1]
Balance at March 31, 2015	$ 1,122us-gaap_AssetRetirementObligation / tve_ReconciliationOfAssetRetirementObligationLiabilityAxis = tve_NonNuclearMember	[1]
[1] The current portion of ARO in the amount of $115 million is included in Accounts payable and accrued liabilities at March 31, 2015.

X

- Definition

The amount of accretion recorded as a regulatory asset during the period.

+ References

No definition available.

+ Details

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X

- Definition

The maximum number of years in between ARO-nuclear decommissioning study updates.

+ References

No definition available.

+ Details

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X

- Definition

Amount recognized for the passage of time, typically for liabilities, that have been discounted to their net present values. Excludes accretion associated with asset retirement obligations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 420

-SubTopic 10

-Section 35

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6394232&loc=d3e17558-110866

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X

- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849



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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Asset Retirement Obligation

-URI http://asc.fasb.org/extlink&oid=6505190

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- Definition

Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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- Definition

Net Increase or Decrease in the asset retirement obligation during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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