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Summary of Significant Accounting Policies General and Basis of Presentation (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 9 Months Ended 3 Months Ended
Jun. 30, 2014
variable_interest_entities
People
Jun. 30, 2013
Jun. 30, 2014
variable_interest_entities
People
Jun. 30, 2013
Sep. 30, 2013
Jun. 30, 2014
Other Noncurrent Assets [Member]
Sep. 30, 2013
Other Noncurrent Assets [Member]
Sep. 30, 2014
Scenario, Forecast [Member]
General and Basis of Presentation                
Population of TVA's service area 9,000,000   9,000,000          
Number of variable interest entities 3   3          
Period of time for customers to fulfill payment arrangements     90 days          
Allowance for uncollectible accounts, accounts receivable $ 1   $ 1   $ 1      
Loans and other long-term receivables, net 96   96   67 105 73  
Loans and other long-term receivables, allowance 10   10   10      
Depreciation expense 391 341 1,100 1,000        
Accelerated depreciation 21   34         21
Total possible amount of payments 160   160          
Payments attributable to BLEU fuel program 101   101          
BLEU fuel obligation $ 16   $ 16