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Nature of Regulation - UNS Energy (Details) - ACC | Mar. 01, 2017 | Aug. 01, 2016 | Jan. 01, 2014 | Jul. 01, 2013 | May 01, 2012
--- | --- | --- | --- | --- | ---
TEP |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
ROE (percent) |  |  |  | 10.00% |
Capital structure of common equity (percent) |  |  |  | 43.50% |
TEP | Subsequent event |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
ROE (percent) | 9.75% |  |  |  |
Capital structure of common equity (percent) | 50.00% |  |  |  |
UNS Electric |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
ROE (percent) |  | 9.50% | 9.50% |  |
Capital structure of common equity (percent) |  | 52.80% | 52.60% |  |
UNS Gas |  |  |  |  |
Public Utilities, General Disclosures [Line Items] |  |  |  |  |
ROE (percent) |  |  |  |  | 9.75%
Capital structure of common equity (percent) |  |  |  |  | 50.80%

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