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Risk Management Activities and Derivative Transactions Risk Management Activities and Derivative Transactions - Derivatives Under Financial Trading Program (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Derivative    
FTP transaction limit $ 130  
Unrealized gains/losses on derivatives 0 0
Natural Gas Futures
    
Derivative    
Notional amount 0 [1] 0 [1]
Fair value 0 [1] 0 [1]
Fuel Oil/Crude Oil Futures
    
Derivative    
Notional amount 0 [1] 0 [1]
Fair value 0 [1] 0 [1]
Natural Gas Swap
    
Derivative    
Notional amount 152,922,500 [1] 294,462,500 [1]
Fair value (169) [1] (232) [1]
Fuel Oil/Crude Oil Swap
    
Derivative    
Notional amount 1,205,000 [1] 1,390,000 [1]
Fair value 3 [1] 4 [1]
Natural Gas Option
    
Derivative    
Notional amount 0 [1] 0 [1]
Fair value 0 [1] 0 [1]
Fuel Oil/Crude Oil Option
    
Derivative    
Notional amount 0 [1] 0 [1]
Fair value 0 [1] 0 [1]
Natural Gas Total Contracts
    
Derivative    
Notional amount 152,922,500 [1] 294,462,500 [1]
Unrealized gains/losses on derivatives (169) (232)
Decrease (increase) in fuel expense (78) (116)
Decrease (increase) in purchased power expense (51) (236)
Fair value (169) [1] (232) [1]
Fuel Oil/Crude Oil Total Contracts
    
Derivative    
Notional amount 1,205,000 [1] 1,390,000 [1]
Unrealized gains/losses on derivatives 3 4
Decrease (increase) in fuel expense 4 10
Fair value 3 [1] 4 [1]
Coal Contract Total Contracts
    
Derivative    
Unrealized gains/losses on derivatives 0 0
Decrease (increase) in fuel expense (1) 0
Fair value 0 0
Closed Derivative Contracts
    
Derivative    
Fair value $ (8) $ (21)
[1] Due to the right of setoff and method of settlement, TVA elects to record commodity derivatives under the FTP based on its net commodity position with the broker or other counterparty. Notional amounts disclosed represent the net absolute value of contractual amounts.