Electric utility segment - Consolidating Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Revenues	$ 725,966	$ 771,535	$ 715,485	$ 661,615	$ 761,650	$ 768,048	$ 685,277	$ 645,874	$ 2,874,601	$ 2,860,849	$ 2,555,625
Expenses
Total expenses									2,525,927	2,527,493	2,209,392
Operating income	100,795	97,308	72,634	77,937	84,604	98,064	78,799	71,889	348,674	333,356	346,233
Allowance for equity funds used during construction									11,987	10,877	12,483
Retirement defined benefits expense—other than service costs									(2,806)	(5,962)	(7,942)
Allowance for borrowed funds used during construction									4,453	4,867	4,778
Income before income taxes									271,409	254,461	276,580
Income taxes									51,637	50,797	109,393
Net income (loss)	66,736	63,890	42,985	46,161	50,046	66,371	46,527	40,720	219,772	203,664	167,187
Preferred stock dividends of subsidiaries									1,890	1,890	1,890
Net income for common stock	66,263	63,419	42,512	45,688	49,573	65,900	46,054	40,247	217,882	201,774	165,297
Parent Company
Expenses
Total expenses									20,335	20,621	17,622
Retirement defined benefits expense—other than service costs									(442)	(674)	(1,119)
Income before income taxes									208,075	193,442	159,765
Income taxes									(9,807)	(8,332)	(5,532)
Net income (loss)									217,882	201,774	165,297
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Income Statements, Captions [Line Items]
Revenues	645,333	688,330	633,784	578,495	680,563	687,409	608,126	570,427	2,545,942	2,546,525	2,257,566
Expenses
Fuel oil									720,709	760,528	587,768
Purchased power									633,256	639,307	586,634
Other operation and maintenance									481,737	461,491	411,907
Depreciation									215,731	203,626	192,784
Taxes, other than income taxes									240,131	239,912	214,949
Total expenses									2,291,564	2,304,864	1,994,042
Operating income	70,331	71,793	55,694	56,560	61,112	74,036	55,144	51,369	254,378	241,661	263,524
Allowance for equity funds used during construction									11,987	10,877	12,483
Equity in earnings of subsidiaries									0	0	0
Retirement defined benefits expense—other than service costs									(2,836)	(3,631)	(6,003)
Interest expense and other charges, net									(70,842)	(73,348)	(69,637)
Allowance for borrowed funds used during construction									4,453	4,867	4,778
Income before income taxes									197,140	180,426	205,145
Income taxes									38,305	34,778	83,199
Net income (loss)	45,860	47,277	33,073	32,625	35,796	50,210	31,668	27,974	158,835	145,648	121,946
Preferred stock dividends of subsidiaries									915	915	915
Net income attributable to Hawaiian Electric									157,920	144,733	121,031
Preferred stock dividends of Hawaiian Electric									1,080	1,080	1,080
Net income for common stock	$ 45,361	$ 46,779	$ 32,574	$ 32,126	$ 35,297	$ 49,712	$ 31,169	$ 27,475	156,840	143,653	119,951
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Parent Company
Condensed Income Statements, Captions [Line Items]
Revenues									1,803,698	1,802,550	1,598,504
Expenses
Fuel oil									494,728	523,706	408,204
Purchased power									494,215	494,450	454,189
Other operation and maintenance									319,771	313,346	274,391
Depreciation									143,470	137,410	130,889
Taxes, other than income taxes									170,979	170,363	152,933
Total expenses									1,623,163	1,639,275	1,420,606
Operating income									180,535	163,275	177,898
Allowance for equity funds used during construction									9,955	9,208	10,896
Equity in earnings of subsidiaries									43,167	45,393	38,057
Retirement defined benefits expense—other than service costs									(2,287)	(2,649)	(5,049)
Interest expense and other charges, net									(51,199)	(52,180)	(48,277)
Allowance for borrowed funds used during construction									3,666	4,019	4,089
Income before income taxes									183,837	167,066	177,614
Income taxes									25,917	22,333	56,583
Net income (loss)									157,920	144,733	121,031
Preferred stock dividends of subsidiaries									0	0	0
Net income attributable to Hawaiian Electric									157,920	144,733	121,031
Preferred stock dividends of Hawaiian Electric									1,080	1,080	1,080
Net income for common stock									156,840	143,653	119,951
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Hawaii Electric Light
Condensed Income Statements, Captions [Line Items]
Revenues									364,590	375,493	333,467
Expenses
Fuel oil									84,565	90,792	63,894
Purchased power									90,989	95,838	87,772
Other operation and maintenance									76,091	70,396	66,184
Depreciation									41,812	40,235	38,741
Taxes, other than income taxes									33,787	34,850	31,184
Total expenses									327,244	332,111	287,775
Operating income									37,346	43,382	45,692
Allowance for equity funds used during construction									816	478	554
Equity in earnings of subsidiaries									0	0	0
Retirement defined benefits expense—other than service costs									(422)	(417)	(93)
Interest expense and other charges, net									(10,741)	(11,836)	(11,799)
Allowance for borrowed funds used during construction									342	276	238
Income before income taxes									27,341	31,883	34,592
Income taxes									5,990	6,868	13,912
Net income (loss)									21,351	25,015	20,680
Preferred stock dividends of subsidiaries									534	534	534
Net income attributable to Hawaiian Electric									20,817	24,481	20,146
Preferred stock dividends of Hawaiian Electric									0	0	0
Net income for common stock									20,817	24,481	20,146
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Maui Electric
Condensed Income Statements, Captions [Line Items]
Revenues									378,202	368,700	325,678
Expenses
Fuel oil									141,416	146,030	115,670
Purchased power									48,052	49,019	44,673
Other operation and maintenance									85,875	77,749	71,332
Depreciation									30,449	25,981	23,154
Taxes, other than income taxes									35,365	34,699	30,832
Total expenses									341,157	333,478	285,661
Operating income									37,045	35,222	40,017
Allowance for equity funds used during construction									1,216	1,191	1,033
Equity in earnings of subsidiaries									0	0	0
Retirement defined benefits expense—other than service costs									(127)	(565)	(861)
Interest expense and other charges, net									(9,450)	(9,550)	(9,644)
Allowance for borrowed funds used during construction									445	572	451
Income before income taxes									29,129	26,870	30,996
Income taxes									6,398	5,577	12,704
Net income (loss)									22,731	21,293	18,292
Preferred stock dividends of subsidiaries									381	381	381
Net income attributable to Hawaiian Electric									22,350	20,912	17,911
Preferred stock dividends of Hawaiian Electric									0	0	0
Net income for common stock									22,350	20,912	17,911
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Other subsidiaries
Condensed Income Statements, Captions [Line Items]
Revenues									0	0	0
Expenses
Fuel oil									0	0	0
Purchased power									0	0	0
Other operation and maintenance									0	0	0
Depreciation									0	0	0
Taxes, other than income taxes									0	0	0
Total expenses									0	0	0
Operating income									0	0	0
Allowance for equity funds used during construction									0	0	0
Equity in earnings of subsidiaries									0	0	0
Retirement defined benefits expense—other than service costs									0	0	0
Interest expense and other charges, net									0		0
Allowance for borrowed funds used during construction									0	0	0
Income before income taxes									0	0	0
Income taxes									0	0	0
Net income (loss)									0	0	0
Preferred stock dividends of subsidiaries									0	0	0
Net income attributable to Hawaiian Electric									0	0	0
Preferred stock dividends of Hawaiian Electric									0	0	0
Net income for common stock									0	0	0
Hawaiian Electric Company, Inc. and Subsidiaries | Consolidating Adjustments
Condensed Income Statements, Captions [Line Items]
Revenues									(548)	(218)	(83)
Expenses
Fuel oil									0	0	0
Purchased power									0	0	0
Other operation and maintenance									0	0	0
Depreciation									0	0	0
Taxes, other than income taxes									0	0	0
Total expenses									0	0	0
Operating income									(548)	(218)	(83)
Allowance for equity funds used during construction									0	0	0
Equity in earnings of subsidiaries									(43,167)	(45,393)	(38,057)
Retirement defined benefits expense—other than service costs									0	0	0
Interest expense and other charges, net									548	218	83
Allowance for borrowed funds used during construction									0	0	0
Income before income taxes									(43,167)	(45,393)	(38,057)
Income taxes									0	0	0
Net income (loss)									(43,167)	(45,393)	(38,057)
Preferred stock dividends of subsidiaries									0	0	0
Net income attributable to Hawaiian Electric									(43,167)	(45,393)	(38,057)
Preferred stock dividends of Hawaiian Electric									0	0	0
Net income for common stock									$ (43,167)	$ (45,393)	$ (38,057)