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Description of Business - Electric Utilities - Caribbean (Details) | Dec. 31, 2016 company MW | Dec. 31, 2015 | Aug. 31, 2015
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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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