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Risk Management Activities - Commodity derivative instruments not designated as hedging instruments (Details) - Non-Hedges - Commodity risk management
Dec. 31, 2020
MWh
J
t
Dec. 31, 2019
MWh
J
t
Electricity    
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]    
Notional amount sold 12,944,000 16,097,000
Notional amount purchased 8,258,000 7,204,000
Natural gas    
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]    
Notional amount sold | J 23,035,000 38,062,000
Notional amount purchased | J 177,448,000 55,023,000
Transmission    
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]    
Notional amount sold 0 0
Notional amount purchased 1,578,000 1,818,000
Emissions    
Disclosure of information about terms and conditions of hedging instruments and how they affect future cash flows [line items]    
Notional amount sold 1,831,000 184,000
Notional amount purchased 2,112,000 138,000
Notional amount sold | t 2,160,000 2,436,000
Notional amount purchased | t 2,365,000 2,446,000