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Electric utility segment - Annual decoupling filings summary (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
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Mar. 31, 2019 | Dec. 31, 2018
Hawaiian Electric (parent only) |  |
Regulatory Projects and Legal Obligations [Line Items] |  |
2019 Annual incremental RAM adjusted revenues | $ 14.0 |
Annual change in accrued RBA balance as of December 31, 2018 (and associated revenue taxes) | (12.2) |
2017 Tax Act Adjustment | 0.0 |
Performance Incentive Mechanism | 0.1 |
Net annual incremental amount to be collected under the tariffs | 1.9 |
HELCO |  |
Regulatory Projects and Legal Obligations [Line Items] |  |
2019 Annual incremental RAM adjusted revenues | 3.5 |
Annual change in accrued RBA balance as of December 31, 2018 (and associated revenue taxes) | (1.9) |
2017 Tax Act Adjustment | 0.0 |
Performance Incentive Mechanism | 0.0 |
Net annual incremental amount to be collected under the tariffs | 1.6 |
Maui Electric |  |
Regulatory Projects and Legal Obligations [Line Items] |  |
2019 Annual incremental RAM adjusted revenues | 3.3 |
Annual change in accrued RBA balance as of December 31, 2018 (and associated revenue taxes) | 0.8 |
2017 Tax Act Adjustment | 2.8 | $ (2.8)
Performance Incentive Mechanism | (0.4) |
Net annual incremental amount to be collected under the tariffs | $ 6.5 |

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