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Electric utility segment - Rate proceedings (Details) - USD ($) $ in Millions | Apr. 17, 2019 | Mar. 18, 2019 | Dec. 14, 2018
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Maui Electric |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |
Interim general rate increase granted | $ 12.2 |  |
Effective interest rate of return | 7.43% |  |
Stipulated ROACE rate | 9.50% |  |
Common equity capitalization rate | 57.00% |  |
Rate Base | $ 454.0 |  |
Risk sharing percentage, ratepayer |  | 98.00% |
Risk sharing percentage, utility |  | 2.00% |
Maximum exposure cap |  | $ 0.6 |
HELCO |  |  |
Regulatory Projects and Legal Obligations [Line Items] |  |  |
Stipulated ROACE rate |  |  | 10.50%
General rate increase, revenue |  |  | $ 13.4
General rate increase, revenue, percent |  |  | 3.40%
Assumptions on rate of return, return on average common equity, percentage decrease |  |  | 8.30%

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