v3.19.3.a.u2

Revenue from contracts - Disaggregation of revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of revenue
Miscellaneous revenue									$ (2.3)	$ (0.3)
Total revenue	$ 66.2	$ 71.1	$ 71.3	$ 73.0	$ 70.7	$ 65.4	$ 66.2	$ 80.0	281.6	282.3	$ 431.0
Solid Fuel
Disaggregation of revenue
Total revenue									80.0	83.8	93.7
Natural Gas
Disaggregation of revenue
Miscellaneous revenue									(2.3)	(0.3)
Total revenue									131.8	139.2	276.8
Hydroelectric
Disaggregation of revenue
Total revenue									68.8	58.3	59.5
Corporate
Disaggregation of revenue
Total revenue									1.0	1.0	1.0
Energy sales
Disaggregation of revenue
Project revenue									138.0	130.9
Total revenue									138.0	130.9	148.9
Energy sales | Solid Fuel
Disaggregation of revenue
Project revenue									41.1	37.4
Energy sales | Natural Gas
Disaggregation of revenue
Project revenue									31.0	38.3
Energy sales | Hydroelectric
Disaggregation of revenue
Project revenue									65.9	55.2
Energy capacity revenue
Disaggregation of revenue
Project revenue									125.4	97.9
Total revenue									125.4	97.9	$ 105.8
Energy capacity revenue | Solid Fuel
Disaggregation of revenue
Project revenue									38.7	41.6
Energy capacity revenue | Natural Gas
Disaggregation of revenue
Project revenue									86.7	56.3
Steam energy and capacity revenue
Disaggregation of revenue
Project revenue									11.7	15.7
Steam energy and capacity revenue | Solid Fuel
Disaggregation of revenue
Project revenue										0.1
Steam energy and capacity revenue | Natural Gas
Disaggregation of revenue
Project revenue									11.7	15.6
Waste heat revenue
Disaggregation of revenue
Project revenue									0.2	0.2
Waste heat revenue | Solid Fuel
Disaggregation of revenue
Project revenue									0.2	0.2
Enhanced dispatch contracts
Disaggregation of revenue
Project revenue										23.9
Enhanced dispatch contracts | Natural Gas
Disaggregation of revenue
Project revenue										23.9
Ancillary and transmission services
Disaggregation of revenue
Project revenue									7.6	13.0
Ancillary and transmission services | Solid Fuel
Disaggregation of revenue
Project revenue										4.5
Ancillary and transmission services | Natural Gas
Disaggregation of revenue
Project revenue									4.7	5.4
Ancillary and transmission services | Hydroelectric
Disaggregation of revenue
Project revenue									2.9	3.1
Asset management and operation
Disaggregation of revenue
Project revenue									1.0	1.0
Asset management and operation | Corporate
Disaggregation of revenue
Project revenue									$ 1.0	$ 1.0

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- Definition

Amount of revenue recognized from sources other than those disaggregated under Topic 606, net of associated expenses.

+ References

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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