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Summary of Significant Accounting Policies General and Basis of Presentation (Details) (USD $)
 3 Months Ended
Dec. 31, 2014
People
variable_interest_entities
Dec. 31, 2013
Sep. 30, 2014
General and Basis of Presentation      
Population of TVA's service area 9,000,000tve_PopulationOfServiceArea    
Amount of appropriation investment that must be repaid     $ 1,000,000,000tve_AmountOfAppropriationInvestmentThatMustBeRepaid
Number of variable interest entities 3tve_NumberOfVariableInterestEntities    
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
Loans Receivable 92,000,000us-gaap_NotesReceivableNet   81,000,000us-gaap_NotesReceivableNet
Loans receivable, allowance 9,000,000us-gaap_AllowanceForNotesAndLoansReceivableNoncurrent   9,000,000us-gaap_AllowanceForNotesAndLoansReceivableNoncurrent
Depreciation expense 380,000,000us-gaap_Depreciation 368,000,000us-gaap_Depreciation  
Total possible amount of payments 160,000,000tve_TotalpossibleamountofBLEUpayments    
Payments attributable to BLEU fuel program 101,000,000tve_PaymentsattributabletoBLEUfuelprogram    
BLEU fuel obligation $ 39,000,000tve_BLEUfuelobligation