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Kingston Fossil Plant Ash Spill (Details) (USD $)
 0 Months Ended 6 Months Ended 36 Months Ended
Dec. 11, 2014
Mar. 31, 2015
Mar. 31, 2015
Dec. 31, 2008
Dredge_cells
Cubic_yards
Kingston Fossil Plant Ash Spill        
Number of dredge cells that failed       1tve_NumberOfDredgeCellsThatFailed
Cubic yards of water and coal fly ash that flowed out of the cell       5,000,000tve_CubicYardsOfWaterAndCoalFlyAshThatFlowedOutOfCell
Total recorded estimate of Kingston cleanup costs   $ 1,100,000,000us-gaap_LossContingencyEstimateOfPossibleLoss $ 1,100,000,000us-gaap_LossContingencyEstimateOfPossibleLoss  
Period collected in rates   15 years    
Kingston cleanup amounts spent to date   1,100,000,000tve_KingstonAmountsSpentToDate 1,100,000,000tve_KingstonAmountsSpentToDate  
Remaining estimated Kingston liability   23,000,000us-gaap_AccrualForEnvironmentalLossContingencies 23,000,000us-gaap_AccrualForEnvironmentalLossContingencies  
Kingston insurance recoveries $ 50,000,000us-gaap_InsuranceRecoveries   $ 317,000,000us-gaap_InsuranceRecoveries