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Commitments and Contingencies (Environmental Accruals) (Details) - CAD
CAD in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Accrual for Environmental Loss Contingencies Disclosure [Abstract]      
Asset Retirement Obligation CAD 170 CAD 109 CAD 106
Nova Scotia Power Inc. [Member]      
Accrual for Environmental Loss Contingencies Disclosure [Abstract]      
Accrual for Environmental Loss Contingencies, Undiscounted, Next Twelve Months 41    
Accrual for Environmental Loss Contingencies, Undiscounted, Second Year Through Fifth Year CAD 41    
Carbon Emission Reduction Targets [Abstract]      
Per cent non-emitting generation sources 90.00%    
Canada's target per cent reduction under the Paris Agreement 30.00%    
Polychlorinated Biphenyl (PCB) Regulations [Member] | Nova Scotia Power Inc. [Member]      
Accrual for Environmental Loss Contingencies Disclosure [Abstract]      
Accrual for Environmental Loss Contingencies CAD 43    
Accrual for Environmental Loss Contingencies, Payments 28 20  
Asset Retirement Obligation CAD 11 CAD 15