Electric utility segment - Condensed consolidating statement of income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Condensed Income Statements, Captions [Line Items]
Revenues	$ 642,946	$ 677,186
Expenses
Total expenses	544,915	617,484
Total operating income	98,031	59,702
Allowance for equity funds used during construction	2,191	2,015
Retirement defined benefits credit (expense)—other than service costs	2,435	(934)
Allowance for borrowed funds used during construction	747	688
Income before income taxes	80,196	39,696
Income taxes	15,365	5,803
Net income	64,831	33,893
Preferred stock dividends of subsidiaries	473	473
Net income for common stock	64,358	33,420
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Revenues	(20)	(215)
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	(20)	(215)
Allowance for equity funds used during construction	0	0
Equity in earnings of subsidiaries	(12,510)	(8,804)
Retirement defined benefits credit (expense)—other than service costs	0	0
Interest expense and other charges, net	20	215
Allowance for borrowed funds used during construction	0	0
Income before income taxes	(12,510)	(8,804)
Income taxes	0
Net income	(12,510)	(8,804)
Preferred stock dividends of subsidiaries	0
Net income attributable to Hawaiian Electric	(12,510)	(8,804)
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	(12,510)	(8,804)
Hawaiian Electric (parent only)
Expenses
Purchased power	142,000	140,000
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	400,554	421,166
Expenses
Fuel oil	88,728	120,535
Purchased power	108,604	107,951
Other operation and maintenance	77,335	85,637
Depreciation	38,914	38,011
Taxes, other than income taxes	38,627	40,501
Total expenses	352,208	392,635
Total operating income	48,346	28,531
Allowance for equity funds used during construction	1,748	1,743
Equity in earnings of subsidiaries	12,510	8,804
Retirement defined benefits credit (expense)—other than service costs	886	(546)
Interest expense and other charges, net	(12,832)	(12,002)
Allowance for borrowed funds used during construction	591	602
Income before income taxes	51,249	27,132
Income taxes	7,621	2,957
Net income	43,628	24,175
Preferred stock dividends of subsidiaries	0	0
Net income attributable to Hawaiian Electric	43,628	24,175
Preferred stock dividends of Hawaiian Electric	270	270
Net income for common stock	43,358	23,905
Hawaii Electric Light | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	85,149	89,293
Expenses
Fuel oil	16,485	22,432
Purchased power	21,597	19,521
Other operation and maintenance	17,912	19,104
Depreciation	10,048	9,760
Taxes, other than income taxes	7,993	8,342
Total expenses	74,035	79,159
Total operating income	11,114	10,134
Allowance for equity funds used during construction	132	119
Equity in earnings of subsidiaries	0	0
Retirement defined benefits credit (expense)—other than service costs	168	194
Interest expense and other charges, net	(2,581)	(2,484)
Allowance for borrowed funds used during construction	44	36
Income before income taxes	8,877	7,999
Income taxes	2,051	1,798
Net income	6,826	6,201
Preferred stock dividends of subsidiaries	134	134
Net income attributable to Hawaiian Electric	6,692	6,067
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	6,692	6,067
Maui Electric | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	79,181	87,198
Expenses
Fuel oil	22,214	30,254
Purchased power	12,095	12,344
Other operation and maintenance	19,323	22,806
Depreciation	8,393	8,079
Taxes, other than income taxes	7,482	8,207
Total expenses	69,507	81,690
Total operating income	9,674	5,508
Allowance for equity funds used during construction	311	153
Equity in earnings of subsidiaries	0	0
Retirement defined benefits credit (expense)—other than service costs	(33)	(29)
Interest expense and other charges, net	(2,590)	(2,323)
Allowance for borrowed funds used during construction	112	50
Income before income taxes	7,474	3,359
Income taxes	1,561	527
Net income	5,913	2,832
Preferred stock dividends of subsidiaries	95	95
Net income attributable to Hawaiian Electric	5,818	2,737
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	5,818	2,737
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 credit (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 Consolidated
Condensed Income Statements, Captions [Line Items]
Revenues	564,864	597,442
Expenses
Fuel oil	127,427	173,221
Purchased power	142,296	139,816
Other operation and maintenance	114,570	127,547
Depreciation	57,355	55,850
Taxes, other than income taxes	54,102	57,050
Total expenses	495,750	553,484
Total operating income	69,114	43,958
Allowance for equity funds used during construction	2,191	2,015
Equity in earnings of subsidiaries	0	0
Retirement defined benefits credit (expense)—other than service costs	1,021	(381)
Interest expense and other charges, net	(17,983)	(16,594)
Allowance for borrowed funds used during construction	747	688
Income before income taxes	55,090	29,686
Income taxes	11,233	5,282
Net income	43,857	24,404
Preferred stock dividends of subsidiaries	229	229
Net income attributable to Hawaiian Electric	43,628	24,175
Preferred stock dividends of Hawaiian Electric	270	270
Net income for common stock	$ 43,358	$ 23,905