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Long-Term Debt - Additional Information (Detail) - USD ($)
$ in Millions
6 Months Ended
May. 20, 2015
Apr. 10, 2015
Jun. 30, 2015
Dec. 31, 2014
Debt Instrument [Line Items]        
Long-term debt, carrying amount     $ 3,851.8 $ 3,628.5
Estimated fair value     4,136.2 3,987.8
Tampa Electric Company [Member]        
Debt Instrument [Line Items]        
Long-term debt, carrying amount     2,263.2 2,097.1
Estimated fair value     $ 2,479.6 $ 2,372.2
TECO Finance [Member] | Floating Rate Notes Due 2018 [Member]        
Debt Instrument [Line Items]        
Aggregate principal amount issued   $ 250.0    
Net proceeds from offering   $ 248.6    
Debt instrument, offering date   Apr. 10, 2015    
Basis spread on federal funds rate   0.60%    
Debt instrument maturity date   Apr. 10, 2018    
Interest rate, description     The 2018 Notes will bear interest at a floating rate that is reset quarterly based on the three-month LIBOR plus 60 basis points, which is payable quarterly on Jan. 10, Apr. 10, July 10 and Oct. 10 of each year, beginning July 10, 2015.  
TECO Finance [Member] | Notes Due in May 2015 [Member]        
Debt Instrument [Line Items]        
Payment of notes   $ 191.0    
The Notes | Tampa Electric Company [Member] | 4.20% Notes Due 2045 [Member]        
Debt Instrument [Line Items]        
Aggregate principal amount issued $ 250.0      
Interest at the initial term rate per annum 4.20%      
Debt instrument principal amount market price percentage 99.814%      
Net proceeds from offering $ 246.8      
Redeemable principal amount percentage 100.00%      
Debt instrument, offering date May 20, 2015      
Debt instrument, start date of redemption Nov. 15, 2044      
Debt instrument, maturity year 2045      
Redeemable principal amount percentage 100.00%      
Basis spread on federal funds rate 0.20%      
Debt instrument maturity date May 15, 2045