Electric utility segment - Condensed consolidating statement of changes in common stock equity (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Increase (decrease) in stockholders' equity
Beginning Balance	$ 2,208,586	$ 2,183,515	$ 2,162,280	$ 2,103,018	$ 2,091,777	$ 2,097,386	$ 2,162,280	$ 2,097,386
Net income for common stock	63,419	42,512	45,688	65,900	46,054	40,247	151,619	152,201
Other comprehensive income, net of taxes	3,297	13,699	9,241	(4,589)	(3,825)	(12,773)	26,237	(21,187)
Common stock dividends	(34,871)	(34,860)	(34,860)	(33,754)	(33,740)	(33,741)
Ending Balance	2,242,689	2,208,586	2,183,515	2,132,045	2,103,018	2,091,777	2,242,689	2,132,045
Consolidating adjustments
Increase (decrease) in stockholders' equity
Beginning Balance			(576,838)			(557,013)	(576,838)	(557,013)
Net income for common stock	(11,048)			(16,636)			(30,983)	(35,041)
Other comprehensive income, net of taxes	0			0			(2)	(1)
Common stock dividends							18,936	20,481
Common stock issuance expenses							1	0
Ending Balance	(588,886)			(571,574)			(588,886)	(571,574)
Hawaiian Electric (parent only) | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance			1,957,641			1,845,283	1,957,641	1,845,283
Net income for common stock	46,779			49,712			111,479	108,356
Other comprehensive income, net of taxes	26			28			73	85
Common stock dividends							(75,939)	(77,479)
Common stock issuance expenses							0	(8)
Ending Balance	1,993,254			1,876,237			1,993,254	1,876,237
HELCO | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance			295,874			286,647	295,874	286,647
Net income for common stock	5,269			9,175			15,104	19,039
Other comprehensive income, net of taxes	0			0			2	1
Common stock dividends							(7,635)	(11,467)
Common stock issuance expenses							0	0
Ending Balance	303,345			294,220			303,345	294,220
Maui Electric | Reportable Legal Entities
Increase (decrease) in stockholders' equity
Beginning Balance			280,863			270,265	280,863	270,265
Net income for common stock	5,779			7,461			15,879	16,002
Other comprehensive income, net of taxes	0			0			0	0
Common stock dividends							(11,301)	(9,014)
Common stock issuance expenses							(1)	0
Ending Balance	285,440			277,253			285,440	277,253
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, net of taxes	0			0			0	0
Common stock dividends							0	0
Common stock issuance expenses							0	0
Ending Balance	101			101			101	101
Hawaiian Electric Company, Inc. and Subsidiaries
Increase (decrease) in stockholders' equity
Beginning Balance	1,971,762	1,964,478	1,957,641	1,852,324	1,846,955	1,845,283	1,957,641	1,845,283
Net income for common stock	46,779	32,574	32,126	49,712	31,169	27,475	111,479	108,356
Other comprehensive income, net of taxes	26	23	24	28	26	31	73	85
Common stock dividends	(25,313)	(25,313)	(25,313)	(25,827)	(25,826)	(25,826)	(75,939)	(77,479)
Common stock issuance expenses						(8)	0	(8)
Ending Balance	$ 1,993,254	$ 1,971,762	$ 1,964,478	$ 1,876,237	$ 1,852,324	$ 1,846,955	$ 1,993,254	$ 1,876,237