Electric utility segment - Condensed consolidating statement of income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Income Statements, Captions [Line Items]
Revenues	$ 645,874	$ 591,562
Expenses
Purchased power	140,000	127,000
Total expenses	573,985	521,824
Total operating income	71,889	69,738
Allowance for equity funds used during construction	3,294	2,399
Retirement defined benefits expense—other than service costs	(1,833)	(1,876)
Allowance for borrowed funds used during construction	1,444	889
Income before income taxes	53,276	51,582
Income taxes	12,556	16,916
Net income	40,720	34,666
Preferred stock dividends of subsidiaries	473	473
Net income for common stock	40,247	34,193
Hawaiian Electric Company
Condensed Income Statements, Captions [Line Items]
Revenues	401,180	362,843
Expenses
Fuel oil	114,498	98,001
Purchased power	107,370	100,147
Other operation and maintenance	72,940	65,993
Depreciation	34,439	32,722
Taxes, other than income taxes	38,167	35,040
Total expenses	367,414	331,903
Total operating income	33,766	30,940
Allowance for equity funds used during construction	2,887	2,056
Equity in earnings of subsidiaries	9,325	8,603
Retirement defined benefits expense—other than service costs	(1,062)	(1,285)
Interest expense and other charges, net	(12,495)	(12,057)
Allowance for borrowed funds used during construction	1,238	749
Income before income taxes	33,659	29,006
Income taxes	5,914	7,271
Net income	27,745	21,735
Preferred stock dividends of subsidiaries	0	0
Net income attributable to Hawaiian Electric	27,745	21,735
Preferred stock dividends of Hawaiian Electric	270	270
Net income for common stock	27,475	21,465
HELCO
Condensed Income Statements, Captions [Line Items]
Revenues	87,933	78,982
Expenses
Fuel oil	18,487	17,257
Purchased power	23,834	18,589
Other operation and maintenance	16,098	15,599
Depreciation	10,055	9,685
Taxes, other than income taxes	8,212	7,450
Total expenses	76,686	68,580
Total operating income	11,247	10,402
Allowance for equity funds used during construction	111	115
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	(103)	83
Interest expense and other charges, net	(2,907)	(3,004)
Allowance for borrowed funds used during construction	64	45
Income before income taxes	8,412	7,641
Income taxes	2,177	2,923
Net income	6,235	4,718
Preferred stock dividends of subsidiaries	134	134
Net income attributable to Hawaiian Electric	6,101	4,584
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	6,101	4,584
Maui Electric
Condensed Income Statements, Captions [Line Items]
Revenues	81,356	76,793
Expenses
Fuel oil	33,983	29,012
Purchased power	8,706	8,388
Other operation and maintenance	18,572	17,225
Depreciation	5,972	5,809
Taxes, other than income taxes	7,725	7,333
Total expenses	74,958	67,767
Total operating income	6,398	9,026
Allowance for equity funds used during construction	296	228
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	(99)	(221)
Interest expense and other charges, net	(2,334)	(2,450)
Allowance for borrowed funds used during construction	142	95
Income before income taxes	4,403	6,678
Income taxes	1,084	2,564
Net income	3,319	4,114
Preferred stock dividends of subsidiaries	95	95
Net income attributable to Hawaiian Electric	3,224	4,019
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	3,224	4,019
Other subsidiaries
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	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
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Revenues	(42)	(7)
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	(42)	(7)
Allowance for equity funds used during construction	0	0
Equity in earnings of subsidiaries	(9,325)	(8,603)
Retirement defined benefits expense—other than service costs	0	0
Interest expense and other charges, net	42	7
Allowance for borrowed funds used during construction	0	0
Income before income taxes	(9,325)	(8,603)
Income taxes	0	0
Net income	(9,325)	(8,603)
Preferred stock dividends of subsidiaries	0	0
Net income attributable to Hawaiian Electric	(9,325)	(8,603)
Preferred stock dividends of Hawaiian Electric	0	0
Net income for common stock	(9,325)	(8,603)
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Income Statements, Captions [Line Items]
Revenues	570,427	518,611
Expenses
Fuel oil	166,968	144,270
Purchased power	139,910	127,124
Other operation and maintenance	107,610	98,817
Depreciation	50,466	48,216
Taxes, other than income taxes	54,104	49,823
Total expenses	519,058	468,250
Total operating income	51,369	50,361
Allowance for equity funds used during construction	3,294	2,399
Equity in earnings of subsidiaries	0	0
Retirement defined benefits expense—other than service costs	(1,264)	(1,423)
Interest expense and other charges, net	(17,694)	(17,504)
Allowance for borrowed funds used during construction	1,444	889
Income before income taxes	37,149	34,722
Income taxes	9,175	12,758
Net income	27,974	21,964
Preferred stock dividends of subsidiaries	229	229
Net income attributable to Hawaiian Electric	27,745	21,735
Preferred stock dividends of Hawaiian Electric	270	270
Net income for common stock	$ 27,475	$ 21,465