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Summary of Significant Accounting Policies General and Basis of Presentation (Details)
People in Millions
 3 Months Ended 12 Months Ended
Dec. 31, 2016
USD ($)
variable_interest_entities
Dec. 31, 2015
USD ($)
Sep. 30, 2016
USD ($)
Dec. 31, 2016
Dec. 31, 2016
People
Dec. 31, 2016
USD ($)
Dec. 31, 2016
Sites
General and Basis of Presentation              
Population of TVA's service area | People         9    
Number of wholly-owned direct subsidiaries       2      
Number of variable interest entities | variable_interest_entities 3            
Allowance for uncollectible accounts, accounts receivable     $ 1,000,000     $ 1,000,000  
Loans receivable, carrying value     130,000,000     142,000,000  
Allowance for loans receivable     8,000,000     8,000,000  
Revenue capitalized during pre-commercial operations $ 14,000,000            
Number of construction projects       2     1
Fuel cost capitalized during pre-commercial operations 5,000,000            
Depreciation expense $ 336,000,000 $ 364,000,000          
Change in depreciation due to new study 56            
AFUDC minimum total project cost     $ 1,000,000,000        
AFUDC capitalized $ 0 $ 58,000,000          
Total estimated amount of BLEU payments           165,000,000  
Payments attributable to BLEU fuel program           151,000,000  
BLEU fuel obligation           $ 14,000,000