Electric utility segment - Condensed consolidating statement of income (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Income Statements, Captions [Line Items]
Revenues	$ 715,485		$ 685,277		$ 1,377,100	$ 1,331,151
Expenses
Purchased power	162,000		161,000		296,000	301,000
Total expenses	642,851		606,478		1,226,529	1,180,463
Total operating income	72,634		78,799		150,571	150,688
Allowance for equity funds used during construction	3,175		2,983		6,085	6,277
Retirement defined benefits expense—other than service costs	(761)		(1,564)		(1,524)	(3,397)
Allowance for borrowed funds used during construction	1,179		1,365		2,257	2,809
Income before income taxes	52,694		59,582		110,733	112,858
Income taxes	9,709		13,055		21,587	25,611
Net income	42,985		46,527		89,146	87,247
Preferred stock dividends of subsidiaries	473		473		946	946
Net income for common stock	42,512	$ 45,688	46,054	$ 40,247	88,200	86,301
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Revenues	(202)		(59)		(234)	(101)
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	(202)		(59)		(234)	(101)
Allowance for equity funds used during construction	0		0		0	0
Equity in earnings of subsidiaries	(8,086)		(9,080)		(19,935)	(18,405)
Retirement defined benefits expense—other than service costs	0		0		0	0
Interest expense and other charges, net	202		59		234	101
Allowance for borrowed funds used during construction	0		0		0	0
Income before income taxes	(8,086)		(9,080)		(19,935)	(18,405)
Income taxes	0		0		0	0
Net income	(8,086)		(9,080)		(19,935)	(18,405)
Preferred stock dividends of subsidiaries	0		0		0	0
Net income attributable to Hawaiian Electric	(8,086)		(9,080)		(19,935)	(18,405)
Preferred stock dividends of Hawaiian Electric	0		0		0	0
Net income for common stock	(8,086)	(11,849)	(9,080)	(9,325)	(19,935)	(18,405)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	450,020		431,699		855,689	832,879
Expenses
Fuel oil	125,431		120,007		234,353	234,505
Purchased power	126,871		121,812		232,094	229,182
Other operation and maintenance	78,551		76,845		159,729	149,785
Depreciation	35,868		34,391		71,735	68,830
Taxes, other than income taxes	42,590		40,951		81,221	79,118
Total expenses	409,311		394,006		779,132	761,420
Total operating income	40,709		37,693		76,557	71,459
Allowance for equity funds used during construction	2,614		2,588		5,061	5,475
Equity in earnings of subsidiaries	8,086		9,080		19,935	18,405
Retirement defined benefits expense—other than service costs	(567)		(554)		(1,134)	(1,616)
Interest expense and other charges, net	(13,390)		(12,930)		(26,190)	(25,425)
Allowance for borrowed funds used during construction	962		1,150		1,864	2,388
Income before income taxes	38,414		37,027		76,093	70,686
Income taxes	5,570		5,588		10,853	11,502
Net income	32,844		31,439		65,240	59,184
Preferred stock dividends of subsidiaries	0		0		0	0
Net income attributable to Hawaiian Electric	32,844		31,439		65,240	59,184
Preferred stock dividends of Hawaiian Electric	270		270		540	540
Net income for common stock	32,574	32,126	31,169	27,475	64,700	58,644
HELCO | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	89,916		89,548		177,121	177,481
Expenses
Fuel oil	19,941		19,432		40,783	37,919
Purchased power	24,029		24,664		43,206	48,498
Other operation and maintenance	18,031		19,015		36,767	35,113
Depreciation	10,453		10,038		20,906	20,093
Taxes, other than income taxes	8,706		8,408		16,811	16,620
Total expenses	81,160		81,557		158,473	158,243
Total operating income	8,756		7,991		18,648	19,238
Allowance for equity funds used during construction	218		124		350	235
Equity in earnings of subsidiaries	0		0		0	0
Retirement defined benefits expense—other than service costs	(105)		(105)		(211)	(208)
Interest expense and other charges, net	(2,920)		(2,922)		(5,821)	(5,829)
Allowance for borrowed funds used during construction	91		77		147	141
Income before income taxes	6,040		5,165		13,113	13,577
Income taxes	1,241		1,269		3,011	3,446
Net income	4,799		3,896		10,102	10,131
Preferred stock dividends of subsidiaries	133		133		267	267
Net income attributable to Hawaiian Electric	4,666		3,763		9,835	9,864
Preferred stock dividends of Hawaiian Electric	0		0		0	0
Net income for common stock	4,666	5,169	3,763	6,101	9,835	9,864
Maui Electric | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	94,050		86,938		179,703	168,294
Expenses
Fuel oil	36,248		32,278		67,093	66,261
Purchased power	11,954		14,262		21,999	22,968
Other operation and maintenance	22,678		16,782		40,894	35,354
Depreciation	7,592		5,932		15,219	11,904
Taxes, other than income taxes	9,147		8,165		17,215	15,890
Total expenses	87,619		77,419		162,420	152,377
Total operating income	6,431		9,519		17,283	15,917
Allowance for equity funds used during construction	343		271		674	567
Equity in earnings of subsidiaries	0		0		0	0
Retirement defined benefits expense—other than service costs	(29)		(329)		(59)	(428)
Interest expense and other charges, net	(2,422)		(2,367)		(4,739)	(4,701)
Allowance for borrowed funds used during construction	126		138		246	280
Income before income taxes	4,449		7,232		13,405	11,635
Income taxes	933		1,819		3,114	2,903
Net income	3,516		5,413		10,291	8,732
Preferred stock dividends of subsidiaries	96		96		191	191
Net income attributable to Hawaiian Electric	3,420		5,317		10,100	8,541
Preferred stock dividends of Hawaiian Electric	0		0		0	0
Net income for common stock	3,420	6,680	5,317	3,224	10,100	8,541
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	0	0
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Income Statements, Captions [Line Items]
Revenues	633,784		608,126		1,212,279	1,178,553
Expenses
Fuel oil	181,620		171,717		342,229	338,685
Purchased power	162,854		160,738		297,299	300,648
Other operation and maintenance	119,260		112,642		237,390	220,252
Depreciation	53,913		50,361		107,860	100,827
Taxes, other than income taxes	60,443		57,524		115,247	111,628
Total expenses	578,090		552,982		1,100,025	1,072,040
Total operating income	55,694		55,144		112,254	106,513
Allowance for equity funds used during construction	3,175		2,983		6,085	6,277
Equity in earnings of subsidiaries	0		0		0	0
Retirement defined benefits expense—other than service costs	(701)		(988)		(1,404)	(2,252)
Interest expense and other charges, net	(18,530)		(18,160)		(36,516)	(35,854)
Allowance for borrowed funds used during construction	1,179		1,365		2,257	2,809
Income before income taxes	40,817		40,344		82,676	77,493
Income taxes	7,744		8,676		16,978	17,851
Net income	33,073		31,668		65,698	59,642
Preferred stock dividends of subsidiaries	229		229		458	458
Net income attributable to Hawaiian Electric	32,844		31,439		65,240	59,184
Preferred stock dividends of Hawaiian Electric	270		270		540	540
Net income for common stock	$ 32,574	$ 32,126	$ 31,169	$ 27,475	$ 64,700	$ 58,644