v3.20.2

Segment and geographic information - risk (Details) - Revenues, net - Consolidated revenue	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Georgia Power
Consolidated revenue concentration
Percentage of consolidated revenue	15.50%	16.20%	11.60%	12.10%
Southern California Edison
Consolidated revenue concentration
Percentage of consolidated revenue		10.50%
Niagara Mohawk
Consolidated revenue concentration
Percentage of consolidated revenue			16.10%	18.40%
Independent Electricity System Operator
Consolidated revenue concentration
Percentage of consolidated revenue	12.20%	11.20%	13.50%	12.10%
BC Hydro
Consolidated revenue concentration
Percentage of consolidated revenue	11.30%		11.20%
Equistar Chemicals, LP
Consolidated revenue concentration
Percentage of consolidated revenue	10.70%	10.40%	10.80%	11.60%

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