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Nature of Regulation - Eastern Canadian Electric Utilities (Details) - company |  |  |  |  | 12 Months Ended
--- | --- | --- | --- | --- | ---
Mar. 01, 2016 | Jan. 01, 2016 | Mar. 01, 2013 | Jan. 01, 2013 | Dec. 31, 2016 | Dec. 31, 2015
Newfoundland Power Inc. | PUB |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
ROE (percent) |  | 8.50% |  | 8.80% |  |
Capital structure of common equity (percent) |  | 45.00% |  | 45.00% |  |
Maritime Electric | IRAC |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
ROE (percent) | 9.35% |  | 9.75% |  |  |
Capital structure of common equity (percent) | 40.00% |  | 40.00% |  |  |
ROE rate term | 3 years |  |  |  |  |
FortisOntario |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Franchise agreement term |  |  |  |  | 35 years |
FortisOntario | Electric Utilities |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Number of utilities |  |  |  |  | 3 |
FortisOntario | OEB |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
Capital structure of common equity (percent) |  |  |  |  | 40.00% | 40.00%
Minimum | FortisOntario | OEB |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
ROE (percent) |  |  |  |  | 8.93% | 8.93%
Maximum | FortisOntario | OEB |  |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |  |
ROE (percent) |  |  |  |  | 9.30% | 9.30%

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