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Electric utility segment Related-Party Transactions (Details) - Hawaiian Electric Industries, Inc. - HECO - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Related Party Transaction [Line Items] |  |  |
Amount charged to subsidiaries for general management and administrative services | $ 7.0 | $ 6.2 | $ 6.1
Effective interest rate basis term | 30 days |  |
Line of credit facility basis point spread (as a percent) | 0.15% |  |

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