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Long-Term Debt - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
6 Months Ended 0 Months Ended 6 Months Ended
Jun. 30, 2014
Dec. 31, 2013
Jun. 30, 2014
Tampa Electric Company [Member]
Dec. 31, 2013
Tampa Electric Company [Member]
May 15, 2014
Tampa Electric Company [Member]
4.35% Notes [Member]
Jun. 30, 2014
Tampa Electric Company [Member]
4.35% Notes [Member]
Debt Instrument [Line Items]            
Long-term debt, carrying amount $ 3,137.6 $ 2,921.1 $ 2,097.2 $ 1,880.8    
Estimated fair value 3,469.6 3,184.1 2,329.6 2,042.0    
Aggregate principal amount issued         300  
Interest at the initial term rate per annum         4.35%  
Debt instrument principal amount market price percentage         99.933%  
Proceeds from notes net of issuance         $ 296.6  
Redeemable principal amount percentage         100.00%  
Libor interest rate           15
Issuance of notes, maturity year         Jan. 01, 2044  
Debt instrument, maturity year         2044  
Debt instrument, stated interest rate         4.35%  
Debt instrument, redemption price percentage         100.00%  
Discount rate, basis points to be added     0.50%   0.15%  
Debt instrument, start date of redemption         Nov. 15, 2043  
Debt instrument, offering date         May 15, 2014