Electric utility segment - Condensed consolidating statement of income (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Condensed Income Statements, Captions [Line Items]
Revenues	$ 641,427			$ 770,882			$ 1,927,558	$ 2,147,982
Expenses
Total expenses	541,866			674,227			1,696,739	1,900,756
Total operating income	99,561			96,655			230,819	247,226
Allowance for equity funds used during construction	2,347			3,250			6,556	9,335
Retirement defined benefits expense—other than service costs	(1,102)			(648)			(2,970)	(2,172)
Allowance for borrowed funds used during construction	801			1,208			2,241	3,465
Income before income taxes	79,521			78,693			179,447	189,426
Income taxes	14,018			14,803			30,691	36,390
Net income	65,503			63,890			148,756	153,036
Preferred stock dividends of subsidiaries	471			471			1,417	1,417
Net income for common stock	65,032	$ 48,887	$ 33,420	63,419	$ 42,512	$ 45,688	147,339	151,619
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Revenues	(110)			(205)			(465)	(439)
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	(110)			(205)			(465)	(439)
Allowance for equity funds used during construction	0			0			0	0
Equity in earnings of subsidiaries	(14,912)			(11,048)			(37,492)	(30,983)
Retirement defined benefits expense—other than service costs	0			0			0	0
Interest expense and other charges, net	110			205			465	439
Allowance for borrowed funds used during construction	0			0			0	0
Income before income taxes	(14,912)			(11,048)			(37,492)	(30,983)
Income taxes				0			0	0
Net income	(14,912)			(11,048)			(37,492)	(30,983)
Preferred stock dividends of subsidiaries				0			0	0
Net income attributable to Hawaiian Electric	(14,912)			(11,048)			(37,492)	(30,983)
Preferred stock dividends of Hawaiian Electric	0			0			0	0
Net income for common stock	(14,912)			(11,048)			(37,492)	(30,983)
Hawaiian Electric (parent only)
Expenses
Purchased power	149,000			176,000			426,000	472,000
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	398,877			491,723			1,200,677	1,347,412
Expenses
Fuel oil	70,557			139,747			268,382	374,100
Purchased power	116,249			135,447			333,146	367,541
Other operation and maintenance	71,179			80,582			231,090	240,311
Depreciation	37,853			35,867			113,724	107,602
Taxes, other than income taxes	38,005			46,433			115,179	127,654
Total expenses	333,843			438,076			1,061,521	1,217,208
Total operating income	65,034			53,647			139,156	130,204
Allowance for equity funds used during construction	1,902			2,685			5,452	7,746
Equity in earnings of subsidiaries	14,912			11,048			37,492	30,983
Retirement defined benefits expense—other than service costs	(591)			(582)			(1,683)	(1,716)
Interest expense and other charges, net	(11,970)			(12,771)			(36,471)	(38,961)
Allowance for borrowed funds used during construction	659			990			1,887	2,854
Income before income taxes	69,946			55,017			145,833	131,110
Income taxes	9,611			7,968			18,724	18,821
Net income	60,335			47,049			127,109	112,289
Preferred stock dividends of subsidiaries	0			0			0	0
Net income attributable to Hawaiian Electric	60,335			47,049			127,109	112,289
Preferred stock dividends of Hawaiian Electric	270			270			810	810
Net income for common stock	60,065			46,779			126,299	111,479
HELCO | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	82,172			93,576			249,970	270,697
Expenses
Fuel oil	17,047			21,427			55,733	62,210
Purchased power	17,665			24,342			53,032	67,548
Other operation and maintenance	17,565			19,868			54,250	56,635
Depreciation	9,760			10,453			29,281	31,359
Taxes, other than income taxes	7,512			8,359			23,324	25,170
Total expenses	69,549			84,449			215,620	242,922
Total operating income	12,623			9,127			34,350	27,775
Allowance for equity funds used during construction	208			229			520	579
Equity in earnings of subsidiaries	0			0			0	0
Retirement defined benefits expense—other than service costs	194			(105)			581	(316)
Interest expense and other charges, net	(2,519)			(2,524)			(7,536)	(8,345)
Allowance for borrowed funds used during construction	65			95			163	242
Income before income taxes	10,571			6,822			28,078	19,935
Income taxes	2,378			1,420			6,372	4,431
Net income	8,193			5,402			21,706	15,504
Preferred stock dividends of subsidiaries	133			133			400	400
Net income attributable to Hawaiian Electric	8,060			5,269			21,306	15,104
Preferred stock dividends of Hawaiian Electric	0			0			0	0
Net income for common stock	8,060			5,269			21,306	15,104
Maui Electric | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	81,629			103,236			244,043	282,939
Expenses
Fuel oil	17,438			37,919			66,599	105,012
Purchased power	15,111			15,248			39,501	37,247
Other operation and maintenance	22,499			23,965			63,491	64,859
Depreciation	8,076			7,615			24,230	22,834
Taxes, other than income taxes	7,534			9,265			22,986	26,480
Total expenses	70,658			94,012			216,807	256,432
Total operating income	10,971			9,224			27,236	26,507
Allowance for equity funds used during construction	237			336			584	1,010
Equity in earnings of subsidiaries	0			0			0	0
Retirement defined benefits expense—other than service costs	(35)			(36)			(93)	(95)
Interest expense and other charges, net	(2,457)			(2,339)			(7,226)	(7,078)
Allowance for borrowed funds used during construction	77			123			191	369
Income before income taxes	8,793			7,308			20,692	20,713
Income taxes	1,846			1,434			4,220	4,548
Net income	6,947			5,874			16,472	16,165
Preferred stock dividends of subsidiaries	95			95			286	286
Net income attributable to Hawaiian Electric	6,852			5,779			16,186	15,879
Preferred stock dividends of Hawaiian Electric	0			0			0	0
Net income for common stock	6,852			5,779			16,186	15,879
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
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	562,568			688,330			1,694,225	1,900,609
Expenses
Fuel oil	105,042			199,093			390,714	541,322
Purchased power	149,025			175,037			425,679	472,336
Other operation and maintenance	111,243			124,415			348,831	361,805
Depreciation	55,689			53,935			167,235	161,795
Taxes, other than income taxes	53,051			64,057			161,489	179,304
Total expenses	474,050			616,537			1,493,948	1,716,562
Total operating income	88,518			71,793			200,277	184,047
Allowance for equity funds used during construction	2,347			3,250			6,556	9,335
Equity in earnings of subsidiaries	0			0			0	0
Retirement defined benefits expense—other than service costs	(432)			(723)			(1,195)	(2,127)
Interest expense and other charges, net	(16,836)			(17,429)			(50,768)	(53,945)
Allowance for borrowed funds used during construction	801			1,208			2,241	3,465
Income before income taxes	74,398			58,099			157,111	140,775
Income taxes	13,835			10,822			29,316	27,800
Net income	60,563			47,277			127,795	112,975
Preferred stock dividends of subsidiaries	228			228			686	686
Net income attributable to Hawaiian Electric	60,335			47,049			127,109	112,289
Preferred stock dividends of Hawaiian Electric	270			270			810	810
Net income for common stock	$ 60,065	$ 42,329	$ 23,905	$ 46,779	$ 32,574	$ 32,126	$ 126,299	$ 111,479