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Derivatives and Risk Management - Additional Information (Details)
12 Months Ended
Dec. 31, 2020
USD ($)
MWh
MMBTU
Dec. 31, 2019
USD ($)
MWh
MMBTU
Canadian [Member]    
Derivative [Line Items]    
Number of days Canadian currency prices are settled with U.S. dollars 60 days  
Interest Rate Swap [Member]    
Derivative [Line Items]    
Letters of credit outstanding | $ $ 0 $ 0
Purchase [Member] | Physical [Member] | Electric Derivative [Member]    
Derivative [Line Items]    
Expected deliveries of energy commodity derivatives after five years | MWh 0  
Expected deliveries of energy commodity derivatives after three years | MWh   0
Purchase [Member] | Physical [Member] | Gas Derivative [Member]    
Derivative [Line Items]    
Expected deliveries of energy commodity derivatives after five years | MMBTU 0  
Expected deliveries of energy commodity derivatives after three years | MMBTU   0
Purchase [Member] | Financial [Member] | Electric Derivative [Member]    
Derivative [Line Items]    
Expected deliveries of energy commodity derivatives after five years | MWh 0  
Expected deliveries of energy commodity derivatives after three years | MWh   0
Purchase [Member] | Financial [Member] | Gas Derivative [Member]    
Derivative [Line Items]    
Expected deliveries of energy commodity derivatives after five years | MMBTU 0  
Expected deliveries of energy commodity derivatives after three years | MMBTU   0
Sales [Member] | Physical [Member] | Electric Derivative [Member]    
Derivative [Line Items]    
Expected deliveries of energy commodity derivatives after five years | MWh 0  
Expected deliveries of energy commodity derivatives after three years | MWh   0
Sales [Member] | Physical [Member] | Gas Derivative [Member]    
Derivative [Line Items]    
Expected deliveries of energy commodity derivatives after five years | MMBTU 0  
Expected deliveries of energy commodity derivatives after three years | MMBTU   0
Sales [Member] | Financial [Member] | Electric Derivative [Member]    
Derivative [Line Items]    
Expected deliveries of energy commodity derivatives after five years | MWh 0  
Expected deliveries of energy commodity derivatives after three years | MWh   0
Sales [Member] | Financial [Member] | Gas Derivative [Member]    
Derivative [Line Items]    
Expected deliveries of energy commodity derivatives after five years | MMBTU 0  
Expected deliveries of energy commodity derivatives after three years | MMBTU   0