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Contingencies and Legal Proceedings Legal Proceedings (Details) | 1 Months Ended | 9 Months Ended | 12 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Jul. 31, 2013 Legal_actions | May. 31, 2013 | Jun. 30, 2012 | Dec. 31, 2011 Legal_actions | Apr. 30, 2011 Groups Agreements | Sep. 30, 2010 | Mar. 31, 2010 People | Nov. 30, 2009 People Legal_actions | Jun. 30, 2008 Legal_actions | Oct. 31, 2007 Legal_actions | Jun. 30, 2015 USD ($) Legal_actions | Dec. 31, 2010 Years | Apr. 30, 2015 Legal_actions | Apr. 14, 2015 Megawatts | Jun. 30, 2011 USD ($) Units Megawatts | Jun. 30, 2010 USD ($)
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Possible additional future costs for compliance with Clean Air Act requirements | $ |  |  |  |  |  |  |  |  |  |  | $ 800,000,000 |  |  |  |  |
Megawatts | Megawatts |  |  |  |  |  |  |  |  |  |  |  |  |  | 700 |  |
Term of payments for civil penalty |  |  |  |  |  |  |  |  |  |  | 3 years |  |  |  |  |
TDEC civil penalties related to Gallatin | $ |  |  |  |  |  |  |  |  |  |  | $ 17,000 |  |  |  |  |
Plaintiff civil penalties related to Gallatin | $ |  |  |  |  |  |  |  |  |  |  | $ 37,500 |  |  |  |  |
Units Affected by Paradise Case |  |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |
Number of claims dismissed related to NPDES permit |  |  |  |  |  |  |  |  |  |  | 7 |  |  |  |  |
Number of claims filed on Gallatin NPDES permit |  |  |  |  |  |  |  |  |  |  | 8 |  |  |  |  |
Number of reactors a CCOLA was submitted for |  |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |
Number of units at John Sevier Fossil |  |  |  |  |  |  |  |  |  |  | 4 |  |  |  |  |
General |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal loss contingency accrual | $ |  |  |  |  |  |  |  |  |  |  | $ 145,000,000 |  |  |  |  |
Environmental Agreements |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of similar environmental agreements entered into | Agreements |  |  |  |  | 2 |  |  |  |  |  |  |  |  |  |  |
Number of environmental agreements entered into with the EPA | Agreements |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |
Number of environmental agreements entered into with Alabama, Kentucky, North Carolina, and Tennessee | Agreements |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |
Number of environmental agreements entered into with environmental advocacy groups | Groups |  |  |  |  | 3 |  |  |  |  |  |  |  |  |  |  |
Number of units to be idled | Units |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 18 |
Megawatts | Megawatts |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,200 |
Megawatts option 2 | Megawatts |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,500 |
Amount to be invested in certain TVA environmental projects | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 290,000,000 |
Amount to be provided to fund environmental projects | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 60,000,000 |
Amount to pay civil penalties | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 10,000,000 |
Kingston Ash Spill |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of lawsuits filed |  |  |  |  |  |  |  |  |  |  | 78 |  |  |  |  |
Number of lawsuits dismissed |  |  |  |  |  |  |  |  |  |  | 15 |  | 2 |  |  |
Loss Contingency, Claims Dismissed, Number |  |  |  |  |  |  |  |  |  |  | 63 |  |  |  |  |
Number of active lawsuits |  |  |  |  |  |  |  |  |  |  | 9 |  |  |  |  |
Payments for Legal Settlements | $ |  |  |  |  |  |  |  |  |  |  | $ 28,000,000 |  |  |  |  |
Loss Contingency, Claims Settled, Number |  |  |  |  |  |  |  |  |  |  | 7 |  |  |  |  |
Civil penalty order issued June 1, 2010 | $ |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 12,000,000
Amount of civil penalty order satisfied | $ |  |  |  |  |  |  |  |  |  |  | $ 10,000,000 |  |  |  |  |
Credit against civil penalty order | $ |  |  |  |  |  |  |  |  |  |  | 2,000,000 |  |  |  |  |
Down payment on natural resource damages | $ |  |  |  |  |  |  |  |  |  |  | 750,000 |  |  |  |  |
Case Involving Tennessee Valley Authority Retirement System |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of participants that filed suit | People |  |  |  |  |  |  | 8 |  |  |  |  |  |  |  |  |
Number of TVARS Board members | People |  |  |  |  |  |  | 6 |  |  |  |  |  |  |  |  |
Retirement age of eligibility for cost of living adjustment before January 1, 2010 | Years |  |  |  |  |  |  |  |  |  |  |  | 55 |  |  |  |
Retirement age of eligibility for cost of living adjustment after January 1, 2010 | Years |  |  |  |  |  |  |  |  |  |  |  | 60 |  |  |  |
Number of days to file an ammended complaint |  |  |  |  |  | 14 days |  |  |  |  |  |  |  |  |  |
Case Involving the NRC Waste Confidence Decision on Spent Nuclear Fuel Storage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of years that spent fuel can be stored after a plant's license is terminated |  |  | 60 years |  |  |  |  |  |  |  |  |  |  |  |  |
Administrative Proceedings Regarding Sequoyah U1 and U2 [Member] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of contentions submitted by BREDL BEST and MATRR |  | 8 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Opposed contentions |  | 8 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of petitioners with standing | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of petitioners | 3 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of contentions dismissed | 7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of contentions left | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Administrative Proceedings Regarding Bellefonte Units 3 and 4 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of contentions left |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
Number of admitted contentions submitted by BREDL and SACE |  |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |
Number of contentions submitted by BREDL and SACE |  |  |  |  |  |  |  |  | 20 |  |  |  |  |  |  |
Number of contentions no longer admitted |  |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |
Administrative Proceedings Regarding Watts Bar Nuclear Plant Unit 2 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of contentions dismissed |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |
Number of contentions admitted for hearing |  |  |  |  |  |  |  | 2 |  |  |  |  |  |  |  |
Number of SACE contentions |  |  |  |  |  |  |  | 7 |  |  |  |  |  |  |  |
Number of other petitioners | People |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |
Number of contentions remaining |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |
Petitions Resulting from Japanese Nuclear Events |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of requests accepted by the NRC |  |  |  | 5 |  |  |  |  |  |  |  |  |  |  |  |
Other Noncurrent Liabilities [Member] | General |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal loss contingency accrual | $ |  |  |  |  |  |  |  |  |  |  | 63,000,000 |  |  |  |  |
Accounts payable and accrued liabilities | General |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal Proceedings |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Legal loss contingency accrual | $ |  |  |  |  |  |  |  |  |  |  | $ 82,000,000 |  |  |  |  |

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