Electric utility segment - Condensed consolidating statement of income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Condensed Income Statements, Captions [Line Items]
Revenues	$ 677,186	$ 661,615
Expenses
Total expenses	617,484	583,678
Total operating income	59,702	77,937
Allowance for equity funds used during construction	2,015	2,910
Retirement defined benefits expense—other than service costs	(934)	(763)
Allowance for borrowed funds used during construction	688	1,078
Income before income taxes	39,696	58,039
Income taxes	5,803	11,878
Net income	33,893	46,161
Preferred stock dividends of subsidiaries	473	473
Net income for common stock	33,420	45,688
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Revenues	(215)	(32)
Expenses
Fuel oil	0	0
Purchased power	0	0
Other operation and maintenance	0	0
Depreciation	0	0
Taxes, other than income taxes	0	0
Total expenses	0	0
Total operating income	(215)	(32)
Allowance for equity funds used during construction	0	0
Equity in earnings of subsidiaries	(8,804)	(11,849)
Retirement defined benefits expense—other than service costs	0	0
Interest expense and other charges, net	215	32
Allowance for borrowed funds used during construction	0	0
Income before income taxes	(8,804)	(11,849)
Income taxes		0
Net income	(8,804)	(11,849)
Preferred stock dividends of subsidiaries		0
Net income attributable to Hawaiian Electric	(8,804)	(11,849)
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	(8,804)	(11,849)
Hawaiian Electric (parent only)
Expenses
Purchased power	140,000	134,000
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	421,166	405,669
Expenses
Fuel oil	120,535	108,922
Purchased power	107,951	105,223
Other operation and maintenance	85,637	81,178
Depreciation	38,011	35,867
Taxes, other than income taxes	40,501	38,631
Total expenses	392,635	369,821
Total operating income	28,531	35,848
Allowance for equity funds used during construction	1,743	2,447
Equity in earnings of subsidiaries	8,804	11,849
Retirement defined benefits expense—other than service costs	(546)	(567)
Interest expense and other charges, net	(12,002)	(12,800)
Allowance for borrowed funds used during construction	602	902
Income before income taxes	27,132	37,679
Income taxes	2,957	5,283
Net income	24,175	32,396
Preferred stock dividends of subsidiaries	0	0
Net income attributable to Hawaiian Electric	24,175	32,396
Preferred stock dividends of Hawaiian Electric	270	270
Net income for common stock	23,905	32,126
HELCO | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	89,293	87,205
Expenses
Fuel oil	22,432	20,842
Purchased power	19,521	19,177
Other operation and maintenance	19,104	18,736
Depreciation	9,760	10,453
Taxes, other than income taxes	8,342	8,105
Total expenses	79,159	77,313
Total operating income	10,134	9,892
Allowance for equity funds used during construction	119	132
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	194	(106)
Interest expense and other charges, net	(2,484)	(2,901)
Allowance for borrowed funds used during construction	36	56
Income before income taxes	7,999	7,073
Income taxes	1,798	1,770
Net income	6,201	5,303
Preferred stock dividends of subsidiaries	134	134
Net income attributable to Hawaiian Electric	6,067	5,169
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	6,067	5,169
Maui Electric | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	87,198	85,653
Expenses
Fuel oil	30,254	30,845
Purchased power	12,344	10,045
Other operation and maintenance	22,806	18,216
Depreciation	8,079	7,627
Taxes, other than income taxes	8,207	8,068
Total expenses	81,690	74,801
Total operating income	5,508	10,852
Allowance for equity funds used during construction	153	331
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	(29)	(30)
Interest expense and other charges, net	(2,323)	(2,317)
Allowance for borrowed funds used during construction	50	120
Income before income taxes	3,359	8,956
Income taxes	527	2,181
Net income	2,832	6,775
Preferred stock dividends of subsidiaries	95	95
Net income attributable to Hawaiian Electric	2,737	6,680
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	2,737	6,680
Other subsidiaries | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	0	0
Expenses
Fuel oil	0	0
Purchased power	0	0
Other operation and maintenance	0	0
Depreciation	0	0
Taxes, other than income taxes	0	0
Total expenses	0	0
Total operating income	0	0
Allowance for equity funds used during construction	0	0
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	0	0
Interest expense and other charges, net	0	0
Allowance for borrowed funds used during construction	0	0
Income before income taxes	0	0
Income taxes		0
Net income	0	0
Preferred stock dividends of subsidiaries	0	0
Net income attributable to Hawaiian Electric	0	0
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	0	0
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Income Statements, Captions [Line Items]
Revenues	597,442	578,495
Expenses
Fuel oil	173,221	160,609
Purchased power	139,816	134,445
Other operation and maintenance	127,547	118,130
Depreciation	55,850	53,947
Taxes, other than income taxes	57,050	54,804
Total expenses	553,484	521,935
Total operating income	43,958	56,560
Allowance for equity funds used during construction	2,015	2,910
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	(381)	(703)
Interest expense and other charges, net	(16,594)	(17,986)
Allowance for borrowed funds used during construction	688	1,078
Income before income taxes	29,686	41,859
Income taxes	5,282	9,234
Net income	24,404	32,625
Preferred stock dividends of subsidiaries	229	229
Net income attributable to Hawaiian Electric	24,175	32,396
Preferred stock dividends of Hawaiian Electric	270	270
Net income for common stock	$ 23,905	$ 32,126