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Income taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Expense (Benefit) [Line Items]
Deferred tax assets, valuation allowance	$ 0	$ 0
Unrecognized tax benefits that would impact effective tax rate	500,000	500,000
Credit adjustments to interest expense on income taxes	(500,000)	100,000	$ (100,000)
Amount of accrued interest related to uncertain tax positions	100,000	600,000
Hawaiian Electric Company, Inc. and Subsidiaries
Income Tax Expense (Benefit) [Line Items]
Unrecognized tax benefits that would impact effective tax rate	11,600,000	0
Credit adjustments to interest expense on income taxes	(300,000)	100,000	$ 100,000
Amount of accrued interest related to uncertain tax positions	$ 100,000	$ 400,000

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[Line Items] for Income Tax Expense (Benefit) [Table]

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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=84230637&loc=d3e32537-109319

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Amount of interest expense accrued for an underpayment of income taxes.

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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=84230637&loc=d3e32718-109319

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Amount of interest expense for an underpayment of income taxes.

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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=84230637&loc=d3e32718-109319

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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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)
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