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Summary of Significant Accounting Policies General and Basis of Presentation (Details) (USD $)
In Millions, unless otherwise specified
 9 Months Ended
Jun. 30, 2013
People
variable_interest_entities
Sep. 30, 2012
General and Basis of Presentation    
Population of TVA's service area 9,000,000  
Number of variable interest entities 2  
Period of time for customers to fulfill payment arrangements 90 days  
Allowance for uncollectible accounts, accounts receivable $ 4 $ 7
Loans and other long-term receivables, net 84 76
Loans and other long-term receivables, allowance 10 12
Accelerated depreciation 14  
Possible amount of future payments 175  
Payments attributable to BLEU fuel program 106  
BLEU fuel obligation $ 6