Income taxes Changes in Unrecognized Tax Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Changes in total unrecognized tax benefits
Unrecognized tax benefits, at the beginning of the period	$ 0.9us-gaap_UnrecognizedTaxBenefits	$ 0.8us-gaap_UnrecognizedTaxBenefits	$ 5.7us-gaap_UnrecognizedTaxBenefits
Additions based on tax positions taken during the year	0	0	0.3
Reductions based on tax positions taken during the year	0	0	0
Additions for tax positions of prior years	0.1	0.5	0
Reductions for tax positions of prior years	0	(0.4)	(4.1)
Settlements	(1.0)	0	0
Lapses of statute of limitations	0	0	(1.1)
Unrecognized tax benefits, at the end of the period	0us-gaap_UnrecognizedTaxBenefits	0.9us-gaap_UnrecognizedTaxBenefits	0.8us-gaap_UnrecognizedTaxBenefits
Hawaiian Electric Company, Inc. and Subsidiaries
Changes in total unrecognized tax benefits
Unrecognized tax benefits, at the beginning of the period	0.5	0.4	3.7
Additions based on tax positions taken during the year	0	0	0.3
Reductions based on tax positions taken during the year	0	0	0
Additions for tax positions of prior years	0.1	0.5	0
Reductions for tax positions of prior years	0	(0.4)	(3.6)
Settlements	(0.6)	0	0
Lapses of statute of limitations	0	0	0
Unrecognized tax benefits, at the end of the period	$ 0	$ 0.5	$ 0.4

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Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

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