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Employee Benefit Plans narrative (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets $ 2,300 $ 2,408  
Contribution Amount 31 23  
TECO Energy Inc [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 2,223 2,153  
Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets 2,300 2,408 $ 2,208
Other Postretirement Benefit Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Fair Value of Plan Assets $ 49 $ 45 $ 39