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Description of Business - Electric Utilities - Caribbean (Details)	Dec. 31, 2016 company MW	Dec. 31, 2015	Aug. 31, 2015
Fortis Turks and Caicos
Public Utilities, General Disclosures [Line Items]
Number of utilities | company	2
Caribbean Utilities
Public Utilities, General Disclosures [Line Items]
Controlling ownership interest (percent)	60.00%	60.00%
Belize Electricity
Public Utilities, General Disclosures [Line Items]
Equity investment ownership (percent)	33.00%		33.00%
Diesel | Caribbean Utilities
Public Utilities, General Disclosures [Line Items]
Generating capacity (MW)	161
Diesel | Fortis Turks and Caicos
Public Utilities, General Disclosures [Line Items]
Generating capacity (MW)	82

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=66011266&loc=d3e33918-111571

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