v3.20.1

Segment and geographic information - risk (Details) - Revenues, net - Consolidated revenue	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Niagara Mohawk
Consolidated revenue concentration
Percentage of consolidated revenue	20.90%	20.10%
Independent Electricity System Operator
Consolidated revenue concentration
Percentage of consolidated revenue	14.70%	15.20%
BC Hydro
Consolidated revenue concentration
Percentage of consolidated revenue	13.50%	12.70%
Equistar Chemicals, LP
Consolidated revenue concentration
Percentage of consolidated revenue	10.30%	12.50%

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