Electric utility segment - Condensed consolidating statement of income (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
Condensed Income Statements, Captions [Line Items]
Revenues	$ 771,535			$ 768,048			$ 2,148,635	$ 2,099,199
Expenses
Purchased power	176,000			177,000			472,000	478,000
Total expenses	674,227			669,984			1,900,756	1,850,447
Total operating income	97,308			98,064			247,879	248,752
Allowance for equity funds used during construction	3,250			1,962			9,335	8,239
Retirement defined benefits expense—other than service costs	(648)			(1,276)			(2,172)	(4,673)
Allowance for borrowed funds used during construction	1,208			1,006			3,465	3,815
Income before income taxes	78,693			77,233			189,426	190,091
Income taxes	14,803			10,862			36,390	36,473
Net income	63,890			66,371			153,036	153,618
Preferred stock dividends of subsidiaries	471			471			1,417	1,417
Net income for common stock	63,419	$ 42,512	$ 45,688	65,900	$ 46,054	$ 40,247	151,619	152,201
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Revenues	(205)			(55)			(439)	(156)
Expenses
Fuel oil	0			0			0	0
Purchased power	0			0			0	0
Other operation and maintenance	0			0			0	0
Depreciation	0			0			0	0
Taxes, other than income taxes	0			0			0	0
Total expenses	0			0			0	0
Total operating income	(205)			(55)			(439)	(156)
Allowance for equity funds used during construction	0			0			0	0
Equity in earnings of subsidiaries	(11,048)			(16,636)			(30,983)	(35,041)
Retirement defined benefits expense—other than service costs	0			0			0	0
Interest expense and other charges, net	205			55			439	156
Allowance for borrowed funds used during construction	0			0			0	0
Income before income taxes	(11,048)			(16,636)			(30,983)	(35,041)
Income taxes	0			0			0	0
Net income	(11,048)			(16,636)			(30,983)	(35,041)
Preferred stock dividends of subsidiaries	0			0			0	0
Net income attributable to Hawaiian Electric	(11,048)			(16,636)			(30,983)	(35,041)
Preferred stock dividends of Hawaiian Electric	0			0			0	0
Net income for common stock	(11,048)			(16,636)			(30,983)	(35,041)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	491,723			488,210			1,347,412	1,321,089
Expenses
Fuel oil	139,747			141,357			374,100	375,862
Purchased power	135,447			138,135			367,541	367,317
Other operation and maintenance	80,582			78,988			240,311	228,773
Depreciation	35,867			34,282			107,602	103,112
Taxes, other than income taxes	46,433			46,096			127,654	125,214
Total expenses	438,076			438,858			1,217,208	1,200,278
Total operating income	53,647			49,352			130,204	120,811
Allowance for equity funds used during construction	2,685			1,648			7,746	7,123
Equity in earnings of subsidiaries	11,048			16,636			30,983	35,041
Retirement defined benefits expense—other than service costs	(582)			(475)			(1,716)	(2,091)
Interest expense and other charges, net	(12,771)			(13,542)			(38,961)	(38,967)
Allowance for borrowed funds used during construction	990			810			2,854	3,198
Income before income taxes	55,017			54,429			131,110	125,115
Income taxes	7,968			4,447			18,821	15,949
Net income	47,049			49,982			112,289	109,166
Preferred stock dividends of subsidiaries	0			0			0	0
Net income attributable to Hawaiian Electric	47,049			49,982			112,289	109,166
Preferred stock dividends of Hawaiian Electric	270			270			810	810
Net income for common stock	46,779			49,712			111,479	108,356
HELCO | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	93,576			98,981			270,697	276,462
Expenses
Fuel oil	21,427			26,429			62,210	64,348
Purchased power	24,342			24,091			67,548	72,589
Other operation and maintenance	19,868			15,253			56,635	50,366
Depreciation	10,453			10,072			31,359	30,165
Taxes, other than income taxes	8,359			9,215			25,170	25,835
Total expenses	84,449			85,060			242,922	243,303
Total operating income	9,127			13,921			27,775	33,159
Allowance for equity funds used during construction	229			39			579	274
Equity in earnings of subsidiaries	0			0			0	0
Retirement defined benefits expense—other than service costs	(105)			(104)			(316)	(312)
Interest expense and other charges, net	(2,524)			(3,026)			(8,345)	(8,855)
Allowance for borrowed funds used during construction	95			49			242	190
Income before income taxes	6,822			10,879			19,935	24,456
Income taxes	1,420			1,571			4,431	5,017
Net income	5,402			9,308			15,504	19,439
Preferred stock dividends of subsidiaries	133			133			400	400
Net income attributable to Hawaiian Electric	5,269			9,175			15,104	19,039
Preferred stock dividends of Hawaiian Electric	0			0			0	0
Net income for common stock	5,269			9,175			15,104	19,039
Maui Electric | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	103,236			100,273			282,939	268,567
Expenses
Fuel oil	37,919			38,765			105,012	105,026
Purchased power	15,248			15,364			37,247	38,332
Other operation and maintenance	23,965			19,312			64,859	54,666
Depreciation	7,615			6,629			22,834	18,533
Taxes, other than income taxes	9,265			9,385			26,480	25,275
Total expenses	94,012			89,455			256,432	241,832
Total operating income	9,224			10,818			26,507	26,735
Allowance for equity funds used during construction	336			275			1,010	842
Equity in earnings of subsidiaries	0			0			0	0
Retirement defined benefits expense—other than service costs	(36)			(103)			(95)	(531)
Interest expense and other charges, net	(2,339)			(2,455)			(7,078)	(7,156)
Allowance for borrowed funds used during construction	123			147			369	427
Income before income taxes	7,308			8,682			20,713	20,317
Income taxes	1,434			1,126			4,548	4,029
Net income	5,874			7,556			16,165	16,288
Preferred stock dividends of subsidiaries	95			95			286	286
Net income attributable to Hawaiian Electric	5,779			7,461			15,879	16,002
Preferred stock dividends of Hawaiian Electric	0			0			0	0
Net income for common stock	5,779			7,461			15,879	16,002
Other subsidiaries | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	0			0			0	0
Expenses
Fuel oil	0			0			0	0
Purchased power	0			0			0	0
Other operation and maintenance	0			0			0	0
Depreciation	0			0			0	0
Taxes, other than income taxes	0			0			0	0
Total expenses	0			0			0	0
Total operating income	0			0			0	0
Allowance for equity funds used during construction	0			0			0	0
Equity in earnings of subsidiaries	0			0			0	0
Retirement defined benefits expense—other than service costs	0			0			0	0
Interest expense and other charges, net	0			0			0	0
Allowance for borrowed funds used during construction	0			0			0	0
Income before income taxes	0			0			0	0
Income taxes	0			0			0	0
Net income	0			0			0	0
Preferred stock dividends of subsidiaries	0			0			0	0
Net income attributable to Hawaiian Electric	0			0			0	0
Preferred stock dividends of Hawaiian Electric	0			0			0	0
Net income for common stock	0			0			0	0
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Income Statements, Captions [Line Items]
Revenues	688,330			687,409			1,900,609	1,865,962
Expenses
Fuel oil	199,093			206,551			541,322	545,236
Purchased power	175,037			177,590			472,336	478,238
Other operation and maintenance	124,415			113,553			361,805	333,805
Depreciation	53,935			50,983			161,795	151,810
Taxes, other than income taxes	64,057			64,696			179,304	176,324
Total expenses	616,537			613,373			1,716,562	1,685,413
Total operating income	71,793			74,036			184,047	180,549
Allowance for equity funds used during construction	3,250			1,962			9,335	8,239
Equity in earnings of subsidiaries	0			0			0	0
Retirement defined benefits expense—other than service costs	(723)			(682)			(2,127)	(2,934)
Interest expense and other charges, net	(17,429)			(18,968)			(53,945)	(54,822)
Allowance for borrowed funds used during construction	1,208			1,006			3,465	3,815
Income before income taxes	58,099			57,354			140,775	134,847
Income taxes	10,822			7,144			27,800	24,995
Net income	47,277			50,210			112,975	109,852
Preferred stock dividends of subsidiaries	228			228			686	686
Net income attributable to Hawaiian Electric	47,049			49,982			112,289	109,166
Preferred stock dividends of Hawaiian Electric	270			270			810	810
Net income for common stock	$ 46,779	$ 32,574	$ 32,126	$ 49,712	$ 31,169	$ 27,475	$ 111,479	$ 108,356