Electric utility segment - Consolidating Statements of Changes in Common Stock Equity (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (decrease) in stockholders' equity
Beginning Balance				$ 2,097,386				$ 2,066,753	$ 2,097,386	$ 2,066,753	$ 1,927,640
Net income for common stock	$ 49,573	$ 65,900	$ 46,054	40,247	$ 32,370	$ 60,073	$ 38,661	34,193	201,774	165,297	248,256
Other comprehensive income (loss), net of tax benefits									(8,669)	(1,372)	(6,867)
Issuance of common stock, net of expenses											26,844
Common stock dividends									(134,987)	(134,873)	(134,050)
Ending Balance	2,162,280				2,097,386				2,162,280	2,097,386	2,066,753
Hawaiian Electric
Increase (decrease) in stockholders' equity
Beginning Balance				1,845,283				1,799,787	1,845,283	1,799,787	1,728,325
Net income for common stock									143,653	119,951	142,317
Other comprehensive income (loss), net of tax benefits									1,318	(688)	(1,247)
Issuance of common stock, net of expenses									70,692	14,000	23,991
Common stock dividends									(103,305)	(87,767)	(93,599)
Ending Balance	1,957,641				1,845,283				1,957,641	1,845,283	1,799,787
Hawaii Electric Light Company, Inc. (HELCO)
Increase (decrease) in stockholders' equity
Beginning Balance				286,647				291,291	286,647	291,291	292,702
Net income for common stock									24,481	20,146	21,255
Other comprehensive income (loss), net of tax benefits									34	2	(154)
Issuance of common stock, net of expenses									1	4	(5)
Common stock dividends									(15,289)	(24,796)	(22,507)
Ending Balance	295,874				286,647				295,874	286,647	291,291
Maui Electric Company, Limited (MECO)
Increase (decrease) in stockholders' equity
Beginning Balance				270,265				259,554	270,265	259,554	263,725
Net income for common stock									20,912	17,911	21,136
Other comprehensive income (loss), net of tax benefits									207	(55)	(46)
Issuance of common stock, net of expenses									1,498	4,801	0
Common stock dividends									(12,019)	(11,946)	(25,261)
Ending Balance	280,863				270,265				280,863	270,265	259,554
Other subsidiaries
Increase (decrease) in stockholders' equity
Beginning Balance				101				101	101	101	101
Net income for common stock									0	0	0
Other comprehensive income (loss), net of tax benefits									0	0	0
Issuance of common stock, net of expenses									0	0	0
Common stock dividends									0	0	0
Ending Balance	101				101				101	101	101
Consolidating adjustments
Increase (decrease) in stockholders' equity
Beginning Balance				(557,013)				(550,946)	(557,013)	(550,946)	(556,528)
Net income for common stock									(45,393)	(38,057)	(42,391)
Other comprehensive income (loss), net of tax benefits									(241)	53	200
Issuance of common stock, net of expenses									(1,499)	(4,805)	5
Common stock dividends									27,308	36,742	47,768
Ending Balance	(576,838)				(557,013)				(576,838)	(557,013)	(550,946)
HECO Consolidated
Increase (decrease) in stockholders' equity
Beginning Balance				1,845,283				1,799,787	1,845,283	1,799,787	1,728,325
Net income for common stock	35,297	$ 49,712	$ 31,169	$ 27,475	25,355	$ 47,487	$ 25,644	$ 21,465	143,653	119,951	142,317
Other comprehensive income (loss), net of tax benefits									1,318	(688)	(1,247)
Issuance of common stock, net of expenses									70,692	14,000	23,991
Common stock dividends									(103,305)	(87,767)	(93,599)
Ending Balance	$ 1,957,641				$ 1,845,283				$ 1,957,641	$ 1,845,283	$ 1,799,787