Electric utility segment - Condensed consolidating statement of income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Income Statements, Captions [Line Items]
Revenues	$ 768,048	$ 673,185	$ 2,099,199	$ 1,897,028
Expenses
Purchased power	177,000	161,000	478,000	441,000
Total expenses	669,984	561,712	1,850,447	1,638,015
Total operating income	98,064	111,473	248,752	259,013
Allowance for equity funds used during construction	1,962	3,482	8,239	8,908
Retirement defined benefits expense—other than service costs	(1,276)	(1,928)	(4,673)	(5,710)
Allowance for borrowed funds used during construction	1,006	1,339	3,815	3,371
Income before income taxes	77,233	95,139	190,091	206,347
Income taxes	10,862	34,595	36,473	72,003
Net income	66,371	60,544	153,618	134,344
Preferred stock dividends of subsidiaries	471	471	1,417	1,417
Net income for common stock	65,900	60,073	152,201	132,927
Consolidating adjustments
Condensed Income Statements, Captions [Line Items]
Revenues	(55)	(30)	(156)	(51)
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	(55)	(30)	(156)	(51)
Allowance for equity funds used during construction	0	0	0	0
Equity in earnings of subsidiaries	(16,636)	(12,767)	(35,041)	(29,306)
Retirement defined benefits expense—other than service costs	0	0	0	0
Interest expense and other charges, net	55	30	156	51
Allowance for borrowed funds used during construction	0	0	0	0
Income before income taxes	(16,636)	(12,767)	(35,041)	(29,306)
Income taxes	0	0	0	0
Net income	(16,636)	(12,767)	(35,041)	(29,306)
Preferred stock dividends of subsidiaries	0	0	0	0
Net income attributable to Hawaiian Electric	(16,636)	(12,767)	(35,041)	(29,306)
Preferred stock dividends of Hawaiian Electric	0	0	0	0
Net income for common stock	(16,636)	(12,767)	(35,041)	(29,306)
Hawaiian Electric (parent only)
Expenses
Other operation and maintenance		64,996		200,648
Total expenses		366,394		1,054,570
Total operating income		62,873		131,954
Retirement defined benefits expense—other than service costs		(1,225)		(3,812)
Hawaiian Electric (parent only) | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	488,210	429,267	1,321,089	1,186,524
Expenses
Fuel oil	141,357	103,959	375,862	301,774
Purchased power	138,135	123,893	367,317	340,498
Other operation and maintenance	78,988	64,996	228,773	200,648
Depreciation	34,282	32,722	103,112	98,167
Taxes, other than income taxes	46,096	40,824	125,214	113,483
Total expenses	438,858	366,394	1,200,278	1,054,570
Total operating income	49,352	62,873	120,811	131,954
Allowance for equity funds used during construction	1,648	3,108	7,123	7,823
Equity in earnings of subsidiaries	16,636	12,767	35,041	29,306
Retirement defined benefits expense—other than service costs	(475)	(1,225)	(2,091)	(3,812)
Interest expense and other charges, net	(13,542)	(11,786)	(38,967)	(36,405)
Allowance for borrowed funds used during construction	810	1,173	3,198	2,910
Income before income taxes	54,429	66,910	125,115	131,776
Income taxes	4,447	19,153	15,949	36,370
Net income	49,982	47,757	109,166	95,406
Preferred stock dividends of subsidiaries	0	0	0	0
Net income attributable to Hawaiian Electric	49,982	47,757	109,166	95,406
Preferred stock dividends of Hawaiian Electric	270	270	810	810
Net income for common stock	49,712	47,487	108,356	94,596
HELCO
Expenses
Other operation and maintenance		16,608		49,850
Total expenses		71,307		212,875
Total operating income		13,027		32,151
Retirement defined benefits expense—other than service costs		15		183
HELCO | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	98,981	84,334	276,462	245,026
Expenses
Fuel oil	26,429	15,754	64,348	47,486
Purchased power	24,091	21,332	72,589	63,403
Other operation and maintenance	15,253	16,608	50,366	49,850
Depreciation	10,072	9,685	30,165	29,056
Taxes, other than income taxes	9,215	7,928	25,835	23,080
Total expenses	85,060	71,307	243,303	212,875
Total operating income	13,921	13,027	33,159	32,151
Allowance for equity funds used during construction	39	167	274	416
Equity in earnings of subsidiaries	0	0	0	0
Retirement defined benefits expense—other than service costs	(104)	15	(312)	183
Interest expense and other charges, net	(3,026)	(2,899)	(8,855)	(8,899)
Allowance for borrowed funds used during construction	49	72	190	172
Income before income taxes	10,879	10,382	24,456	24,023
Income taxes	1,571	3,815	5,017	8,973
Net income	9,308	6,567	19,439	15,050
Preferred stock dividends of subsidiaries	133	133	400	400
Net income attributable to Hawaiian Electric	9,175	6,434	19,039	14,650
Preferred stock dividends of Hawaiian Electric	0	0	0	0
Net income for common stock	9,175	6,434	19,039	14,650
Maui Electric
Expenses
Other operation and maintenance		17,077		51,939
Total expenses		72,571		211,470
Total operating income		12,627		31,286
Retirement defined benefits expense—other than service costs		(211)		(650)
Maui Electric | Reportable Legal Entities
Condensed Income Statements, Captions [Line Items]
Revenues	100,273	85,198	268,567	242,756
Expenses
Fuel oil	38,765	26,545	105,026	82,527
Purchased power	15,364	15,122	38,332	36,637
Other operation and maintenance	19,312	17,077	54,666	51,939
Depreciation	6,629	5,799	18,533	17,355
Taxes, other than income taxes	9,385	8,028	25,275	23,012
Total expenses	89,455	72,571	241,832	211,470
Total operating income	10,818	12,627	26,735	31,286
Allowance for equity funds used during construction	275	207	842	669
Equity in earnings of subsidiaries	0	0	0	0
Retirement defined benefits expense—other than service costs	(103)	(211)	(531)	(650)
Interest expense and other charges, net	(2,455)	(2,252)	(7,156)	(7,372)
Allowance for borrowed funds used during construction	147	94	427	289
Income before income taxes	8,682	10,465	20,317	24,222
Income taxes	1,126	4,037	4,029	9,280
Net income	7,556	6,428	16,288	14,942
Preferred stock dividends of subsidiaries	95	95	286	286
Net income attributable to Hawaiian Electric	7,461	6,333	16,002	14,656
Preferred stock dividends of Hawaiian Electric	0	0	0	0
Net income for common stock	7,461	6,333	16,002	14,656
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
Hawaiian Electric Company, Inc. and Subsidiaries
Condensed Income Statements, Captions [Line Items]
Revenues	687,409	598,769	1,865,962	1,674,255
Expenses
Fuel oil	206,551	146,258	545,236	431,787
Purchased power	177,590	160,347	478,238	440,538
Other operation and maintenance	113,553	98,681	333,805	302,437
Depreciation	50,983	48,206	151,810	144,578
Taxes, other than income taxes	64,696	56,780	176,324	159,575
Total expenses	613,373	510,272	1,685,413	1,478,915
Total operating income	74,036	88,497	180,549	195,340
Allowance for equity funds used during construction	1,962	3,482	8,239	8,908
Equity in earnings of subsidiaries	0	0	0	0
Retirement defined benefits expense—other than service costs	(682)	(1,421)	(2,934)	(4,279)
Interest expense and other charges, net	(18,968)	(16,907)	(54,822)	(52,625)
Allowance for borrowed funds used during construction	1,006	1,339	3,815	3,371
Income before income taxes	57,354	74,990	134,847	150,715
Income taxes	7,144	27,005	24,995	54,623
Net income	50,210	47,985	109,852	96,092
Preferred stock dividends of subsidiaries	228	228	686	686
Net income attributable to Hawaiian Electric	49,982	47,757	109,166	95,406
Preferred stock dividends of Hawaiian Electric	270	270	810	810
Net income for common stock	$ 49,712	$ 47,487	$ 108,356	$ 94,596