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Kingston Fossil Plant Ash Spill (Details) (USD $)
 3 Months Ended 30 Months Ended
Dec. 31, 2014
Sep. 30, 2014
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    
Period collected in rates 15 years    
Kingston cleanup amounts spent to date 1,100,000,000tve_KingstonAmountsSpentToDate    
Remaining estimated Kingston liability 12,000,000us-gaap_AccrualForEnvironmentalLossContingencies    
Kingston insurance recoveries $ 50,000,000us-gaap_InsuranceRecoveries $ 317,000,000us-gaap_InsuranceRecoveries