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Summary of Significant Accounting Policies General and Basis of Presentation (Details) (USD $)
 3 Months Ended 6 Months Ended
Mar. 31, 2015
People
variable_interest_entities
Mar. 31, 2014
Mar. 31, 2015
People
variable_interest_entities
Mar. 31, 2014
Sep. 30, 2014
General and Basis of Presentation          
Population of TVA's service area 9,000,000tve_PopulationOfServiceArea   9,000,000tve_PopulationOfServiceArea    
Amount of appropriation investment that must be repaid         $ 1,000,000,000tve_AmountOfAppropriationInvestmentThatMustBeRepaid
Number of variable interest entities 3tve_NumberOfVariableInterestEntities   3tve_NumberOfVariableInterestEntities    
Reclassification from Environmental cleanup costs-Kingston ash spill-non cash to Other, net     34,000,000tve_ReclassificationfromEnvironmentalcleanupcostsKingstonashspillnoncashtoOthernet    
Reclassification from Environmental cleanup costs-Kingston ash spill to Other, net     (43,000,000)tve_ReclassificationfromEnvironmentalcleanupcostsKingstonashspilltoOthernet    
Reclassification to Other, net from Environmental cleanup costs-Kingston ash spill-non cash and Environmental cleanup costs-Kingston ash spill     (9,000,000)tve_ReclassificationtoOthernetfromEnvironmentalcleanupcostsKingstonashspillnoncashandEnvironmentalcleanupcostsKingstonashspill    
Period of time for customers to fulfill payment arrangements     90 days    
Allowance for uncollectible accounts, accounts receivable 1,000,000us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent   1,000,000us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent   1,000,000us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent
Loans receivable 110,000,000us-gaap_NotesReceivableNet   110,000,000us-gaap_NotesReceivableNet   81,000,000us-gaap_NotesReceivableNet
Loans receivable, allowance 8,000,000us-gaap_AllowanceForNotesAndLoansReceivableNoncurrent   8,000,000us-gaap_AllowanceForNotesAndLoansReceivableNoncurrent   9,000,000us-gaap_AllowanceForNotesAndLoansReceivableNoncurrent
Depreciation expense 383,000,000us-gaap_Depreciation 382,000,000us-gaap_Depreciation 763,000,000us-gaap_Depreciation 750,000,000us-gaap_Depreciation  
Total possible amount of payments 162,000,000tve_TotalpossibleamountofBLEUpayments   162,000,000tve_TotalpossibleamountofBLEUpayments    
Payments attributable to BLEU fuel program 101,000,000tve_PaymentsattributabletoBLEUfuelprogram   101,000,000tve_PaymentsattributabletoBLEUfuelprogram    
BLEU fuel obligation $ 39,000,000tve_BLEUfuelobligation   $ 39,000,000tve_BLEUfuelobligation