Summary of significant accounting policies (Tables)

12 Months Ended

Dec. 31, 2020

Summary of significant accounting policies

Summary of derivative instruments not designated, treatment of changes in fair value and cash settlements

Derivative financial instrument	Classification of changes in fair value	Classification of cash settlements
Natural gas swaps	Change in fair value of derivative instrument	Fuel expense
Fuel purchase agreements	Change in fair value of derivative instrument	Fuel expense
Interest rate swaps	Change in fair value of derivative instrument	Interest expense, net
Convertible debenture conversion option	Other (income) expense, net	NA
Foreign currency forward contract	Foreign exchange loss	Foreign exchange loss