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Proposed merger (Details) |  | 1 Months Ended
--- | --- | ---
Dec. 03, 2014 USD ($) $ / shares shares | Jan. 31, 2015 USD ($) | Dec. 31, 2014 complaint
Business Acquisition [Line Items] |  |  |
Number of purported class action complaints filed | complaint |  |  | 8
NextEra Energy, Inc Merger |  |  |
Business Acquisition [Line Items] |  |  |
Merger share conversion ratio | shares | 0.2413 |  |
Minimum percentage of shares from which holders approval needed for merger | 75.00% |  |
Merger agreement contract extension | 6 months |  |
Merger contract termination fee | $ 90,000,000 |  |
Maximum expenses paid to party for cancellation of merger | $ 5,000,000 |  |
Subsequent event | NextEra Energy, Inc Merger |  |  |
Business Acquisition [Line Items] |  |  |
Minimum period that entity agrees not to submit applications for general base rate increase |  | 4 years |
Approximate amount of cumulative savings for customers due to forgone recoveries |  | $ 60,000,000 |
Hawaiian Electric Company, Inc. and Subsidiaries | NextEra Energy, Inc Merger |  |  |
Business Acquisition [Line Items] |  |  |
Special dividend | $ / shares | $ 0.50 |  |

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