Shareholders' equity - Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	$ 2,162,280	$ 2,097,386	$ 2,066,753
Current period other comprehensive income (loss) and reclassifications, net of taxes	30,571	(8,669)	(1,372)
Reclass of AOCI for tax rate reduction impact1			(7,440)
Ending Balance	2,280,260	2,162,280	2,097,386
Hawaiian Electric Company, Inc. and Subsidiaries
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	1,957,641	1,845,283	1,799,787
Current period other comprehensive income (loss) and reclassifications, net of taxes	(1,378)	1,318	(688)
Reclass of AOCI for tax rate reduction impact1			(209)
Ending Balance	2,047,352	1,957,641	1,845,283
AOCI
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(50,610)	(41,941)	(33,129)
Current period other comprehensive income (loss) and reclassifications, net of taxes	30,571	(8,669)	(1,372)
Ending Balance	(20,039)	(50,610)	(41,941)
AOCI \| Hawaiian Electric Company, Inc. and Subsidiaries
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	99	(1,219)	(322)
Current period other comprehensive income (loss) and reclassifications, net of taxes	(1,378)	1,318	(688)
Reclass of AOCI for tax rate reduction impact1			(209)
Ending Balance	(1,279)	99	(1,219)
Net unrealized gains (losses) on securities
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(24,423)	(14,951)	(7,931)
Current period other comprehensive income (loss) and reclassifications, net of taxes	26,904	(9,472)	(4,370)
Reclass of AOCI for tax rate reduction impact1			(2,650)
Ending Balance	2,481	(24,423)	(14,951)
Unrealized gains (losses) on derivatives
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(436)	0	(454)
Current period other comprehensive income (loss) and reclassifications, net of taxes	(1,177)	(436)	454
Reclass of AOCI for tax rate reduction impact1			0
Ending Balance	(1,613)	(436)	0
Unrealized gains (losses) on derivatives \| Hawaiian Electric Company, Inc. and Subsidiaries
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	0	0	(454)
Current period other comprehensive income (loss) and reclassifications, net of taxes	0	0	454
Reclass of AOCI for tax rate reduction impact1			0
Ending Balance	0	0	0
Retirement benefit plans
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	(25,751)	(26,990)	(24,744)
Current period other comprehensive income (loss) and reclassifications, net of taxes	4,844	1,239	2,544
Reclass of AOCI for tax rate reduction impact1			(4,790)
Ending Balance	(20,907)	(25,751)	(26,990)
Retirement benefit plans \| Hawaiian Electric Company, Inc. and Subsidiaries
AOCI Attributable to Parent [Roll Forward]
Beginning Balance	99	(1,219)	132
Current period other comprehensive income (loss) and reclassifications, net of taxes	(1,378)	1,318	(1,142)
Reclass of AOCI for tax rate reduction impact1			(209)
Ending Balance	$ (1,279)	$ 99	$ (1,219)

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount after tax of other comprehensive income (loss) attributable to parent entity.

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- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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- Definition

Amount of increase (decrease) in accumulated other comprehensive income (AOCI) for reclassification to retained earnings of tax effect from remeasurement of deferred tax pursuant to Tax Cuts and Jobs Act.

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