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Income taxes - Additional Information (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Income Tax Expense (Benefit) [Line Items] |  |  |
Deferred tax assets, valuation allowance | $ 0.0 | $ 0.0 |
Unrecognized tax benefits that would impact effective tax rate | 10.2 | 11.6 |
Credit adjustments to interest expense on income taxes | 0.2 | (0.5) | $ 0.1
Amount of accrued interest related to uncertain tax positions | 0.3 | 0.1 |
Hawaiian Electric Company, Inc. and Subsidiaries |  |  |
Income Tax Expense (Benefit) [Line Items] |  |  |
Unrecognized tax benefits that would impact effective tax rate | 10.2 | 11.6 |
Credit adjustments to interest expense on income taxes | 0.1 | (0.3) | $ 0.1
Amount of accrued interest related to uncertain tax positions | $ 0.1 | $ 0.1 |

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- Definition Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32537-109319 + Details
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- Definition Amount of interest expense accrued for an underpayment of income taxes. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=121826272&loc=d3e32718-109319 + Details
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- Definition The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121826272&loc=SL6600010-109319 + Details
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