Electric utility segment - Condensed consolidating statement of changes in common stock equity (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Increase (decrease) in stockholders' equity
Beginning Balance		$ 2,280,260	$ 2,183,515	$ 2,162,280	$ 2,280,260	$ 2,162,280
Net income for common stock	$ 48,887	33,420	42,512	45,688	82,307	88,200
Other comprehensive income (loss), net of taxes	(332)	18,212	13,699	9,241	17,880	22,940
Common stock dividends	(36,017)	(36,019)	(34,860)	(34,860)
Ending Balance	2,291,398		2,208,586	2,183,515	2,291,398	2,208,586
Consolidating adjustments
Increase (decrease) in stockholders' equity
Beginning Balance		(591,969)		(576,838)	(591,969)	(576,838)
Net income for common stock	(13,776)		(8,086)		(22,580)	(19,935)
Other comprehensive income (loss), net of taxes	0		(1)		(1)	(2)
Common stock dividends					15,352	12,624
Common stock issuance expenses						2
Ending Balance	(599,198)		(584,149)		(599,198)	(584,149)
Hawaiian Electric (parent only) | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance		2,047,352		1,957,641	2,047,352	1,957,641
Net income for common stock	42,329		32,574		66,234	64,700
Other comprehensive income (loss), net of taxes	25		23		51	47
Common stock dividends					(53,568)	(50,626)
Ending Balance	2,060,069		1,971,762		2,060,069	1,971,762
HELCO | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance		298,998		295,874	298,998	295,874
Net income for common stock	7,179		4,666		13,246	9,835
Other comprehensive income (loss), net of taxes	3		1		4	2
Common stock dividends					(8,160)	(5,090)
Common stock issuance expenses						(2)
Ending Balance	304,088		300,619		304,088	300,619
Maui Electric | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance		292,870		280,863	292,870	280,863
Net income for common stock	6,597		3,420		9,334	10,100
Other comprehensive income (loss), net of taxes	(3)		0		(3)	0
Common stock dividends					(7,192)	(7,534)
Ending Balance	295,009		283,429		295,009	283,429
Other subsidiaries | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance		101		101	101	101
Net income for common stock	0		0		0	0
Other comprehensive income (loss), net of taxes	0		0		0	0
Ending Balance	101		101		101	101
Hawaiian Electric Company, Inc. and Subsidiaries
Increase (decrease) in stockholders' equity
Beginning Balance	2,044,499	2,047,352	1,964,478	1,957,641	2,047,352	1,957,641
Net income for common stock	42,329	23,905	32,574	32,126	66,234	64,700
Other comprehensive income (loss), net of taxes	25	26	23	24	51	47
Common stock dividends	(26,784)	(26,784)	(25,313)	(25,313)	(53,568)	(50,626)
Common stock issuance expenses						0
Ending Balance	$ 2,060,069	$ 2,044,499	$ 1,971,762	$ 1,964,478	$ 2,060,069	$ 1,971,762