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Income taxes Additional Information (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Income Tax Expense (Benefit) [Line Items]      
Federal current taxes $ (10,970) $ (1,520) $ (15,411)
Federal deferred taxes $ 91,159 $ 73,680 $ 82,138
Reconciliation percentage of amount of income taxes computed at federal statutory rate 35.00% 35.00% 35.00%
Amount of decrease in deferred taxes related to tax gross-up of AFUDC-equity   $ 3,500  
Out-of-period income tax benefit   3,100  
Out-of-period tax benefit related to utilities   2,700  
Credit adjustments to interest expense on income taxes $ 1,700 300 $ 1,400
Amount of accrued interest related to uncertain tax positions   400  
Difference      
Income Tax Expense (Benefit) [Line Items]      
Federal current taxes (44,732)    
Federal deferred taxes 44,732    
Hawaiian Electric Company, Inc. and Subsidiaries      
Income Tax Expense (Benefit) [Line Items]      
Federal current taxes 1,108 1,313 (26,965)
Federal deferred taxes 68,775 58,024 79,437
Net operating loss carryforwards 52,000    
Credit adjustments to interest expense on income taxes $ 700 $ 300 $ 500