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Electric utility segment - Related-Party Transactions (Details) - Hawaiian Electric Industries, Inc. - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Hamakua Energy Partners, L.P. (HEP) |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Amount charged to subsidiaries for general management and administrative services | $ 3.0 | $ 56.0 |  |
Hawaiian Electric Company, Inc (HECO) |  |  |  |
Related Party Transaction [Line Items] |  |  |  |
Amount charged to subsidiaries for general management and administrative services |  | $ 5.9 | $ 6.2 | $ 6.5
Effective interest rate basis term |  | 30 days |  |
Line of credit facility basis point spread |  | 0.15% |  |

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