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Short Term Debt (short-term revolving and non-revolving credit facilities, outstanding borrowings and available capacity) (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Short term debt revolving and non revolving credit facility [Member]    
Short-term Debt [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 2,024 $ 1,762
Credit Facility Advances 1,241 960
Letters of Credit Outstanding, Amount 3 3
Total advances under available facilities 1,244 963
Available capacity under existing agreements 780 799
TECO Energy Inc. and TECO Finance Inc. [Member] | Revolving Credit Facility [Member]    
Short-term Debt [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 376 $ 403
Line of Credit Facility, Expiration Date Mar. 22, 2022 Dec. 17, 2018
TECO Energy Inc. and TECO Finance Inc. [Member] | Finance Term Credit Facility [Member]    
Short-term Debt [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 502 $ 537
Line of Credit Facility, Expiration Date Dec. 31, 2018  
Tampa Electric Division [Member] | Revolving Credit Facility [Member]    
Short-term Debt [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 408 436
Line of Credit Facility, Expiration Date Mar. 22, 2022  
Tampa Electric Division [Member] | Accounts Receivable Revolving Credit Facility    
Short-term Debt [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 188 201
Line of Credit Facility, Expiration Date Dec. 31, 2018  
Tampa Electric Division [Member] | Finance Term Credit Facility [Member]    
Short-term Debt [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 377 0
Line of Credit Facility, Expiration Date Nov. 01, 2018  
New Mexico Gas Company [Member] | Revolving Credit Facility [Member]    
Short-term Debt [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 157 $ 168
Line of Credit Facility, Expiration Date Mar. 22, 2022 Dec. 17, 2018
Grand Bahama Power Company Limited [Member] | Revolving Credit Facility [Member]    
Short-term Debt [Line Items]    
Line of Credit Facility, Maximum Borrowing Capacity $ 16 $ 17