Acquisitions, Investments and Dispositions - Upton 2 (Details) - Con Edison Development $ in Millions	1 Months Ended	12 Months Ended
May 31, 2017 USD ($)	Dec. 31, 2018 MW
Upton 2
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Generating capacity (MW AC) \| MW		180
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Upton 2
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration the project is sold	$ 11.0
Gain on sale of project	1.0
Gain on sale of project, net of tax	$ 0.7

Amount before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

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