Commitments and Contingencies - Purchased Power Agreements (Details) - MW	Jun. 30, 2020	Dec. 31, 2019
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Variable Interest Entity [Line Items]
Generating capacity under long term purchased power agreements (in MW)	1,518	1,442

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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