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CAPITAL AND FINANCIAL RISK MANAGEMENT - Energy price risk (Details) - Price Risk
$ in Millions
12 Months Ended
Dec. 31, 2020
USD ($)
Capital and financial risk management  
Percentage of increase in price 10.00%
Percentage of decrease in price 10.00%
Increase in price Effect on OCI before taxes, gain (loss) $ 11.4
Decrease in price Effect on OCI before taxes, gain (loss) $ (11.3)