For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
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Segment and geographic information - risk (Details) - Revenues, net - Consolidated revenue	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Georgia Power
Consolidated revenue concentration
Percentage of consolidated revenue	11.40%	11.10%		10.10%
Niagara Mohawk
Consolidated revenue concentration
Percentage of consolidated revenue	18.40%	23.70%	19.70%	22.60%
Independent Electricity System Operator
Consolidated revenue concentration
Percentage of consolidated revenue	13.20%	11.30%	14.00%	12.50%
BC Hydro
Consolidated revenue concentration
Percentage of consolidated revenue		10.80%	11.90%	10.10%
Equistar Chemicals, LP
Consolidated revenue concentration
Percentage of consolidated revenue	11.30%	11.00%	10.80%	12.20%