Electric utility segment - Consolidating Statement of Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues	$ 658,597	$ 673,185	$ 632,281	$ 591,562	$ 617,395	$ 646,055	$ 566,244	$ 550,960	$ 2,555,625	$ 2,380,654	$ 2,602,982
Expenses
Purchased power									587,000	563,000	594,000
Total expenses									2,217,334	2,032,479	2,280,429
Operating income	84,988	109,545	75,896	67,862	88,427	105,442	85,455	68,851	338,291	348,175	322,553
Allowance for equity funds used during construction									12,483	8,325	6,928
Allowance for borrowed funds used during construction									4,778	3,144	2,457
Income before income taxes									276,580	373,841	254,788
Income taxes									109,393	123,695	93,021
Net income (loss)	32,843	60,544	39,134	34,666	45,107	127,613	44,601	32,825	167,187	250,146	161,767
Preferred stock dividends of subsidiaries									1,890	1,890	1,890
Net income for common stock	32,370	60,073	38,661	34,193	44,634	127,142	44,128	32,352	165,297	248,256	159,877
Hawaiian Electric Company, Inc (HECO)
Revenues									1,598,504	1,474,384	1,644,181
Expenses
Fuel oil									408,204	305,359	458,069
Purchased power									454,189	431,009	440,983
Other operation and maintenance									279,440	273,176	284,583
Depreciation									130,889	126,086	117,682
Taxes, other than income taxes									152,933	141,615	156,871
Total expenses									1,425,655	1,277,245	1,458,188
Operating income									172,849	197,139	185,993
Allowance for equity funds used during construction									10,896	6,659	5,641
Equity in earnings of subsidiaries									38,057	42,391	42,920
Interest expense and other charges, net									(48,277)	(45,839)	(45,899)
Allowance for borrowed funds used during construction									4,089	2,484	1,967
Income before income taxes									177,614	202,834	190,622
Income taxes									56,583	59,437	53,828
Net income (loss)									121,031	143,397	136,794
Preferred stock dividends of subsidiaries									0	0	0
Net income attributable to Hawaiian Electric									121,031	143,397	136,794
Preferred stock dividends of Hawaiian Electric									1,080	1,080	1,080
Net income for common stock									119,951	142,317	135,714
Hawaii Electric Light Company, Inc. (HELCO)
Revenues									333,467	311,385	345,549
Expenses
Fuel oil									63,894	55,094	71,851
Purchased power									87,772	81,018	97,503
Other operation and maintenance									66,277	63,897	63,098
Depreciation									38,741	37,797	37,250
Taxes, other than income taxes									31,184	29,017	32,312
Total expenses									287,868	266,823	302,014
Operating income									45,599	44,562	43,535
Allowance for equity funds used during construction									554	765	604
Equity in earnings of subsidiaries									0	0	0
Interest expense and other charges, net									(11,799)	(11,555)	(10,773)
Allowance for borrowed funds used during construction									238	294	215
Income before income taxes									34,592	34,066	33,581
Income taxes									13,912	12,277	12,292
Net income (loss)									20,680	21,789	21,289
Preferred stock dividends of subsidiaries									534	534	534
Net income attributable to Hawaiian Electric									20,146	21,255	20,755
Preferred stock dividends of Hawaiian Electric									0	0	0
Net income for common stock									20,146	21,255	20,755
Maui Electric Company, Limited (MECO)
Revenues									325,678	308,705	345,517
Expenses
Fuel oil									115,670	94,251	124,680
Purchased power									44,673	50,713	55,610
Other operation and maintenance									72,193	68,460	65,408
Depreciation									23,154	23,178	22,448
Taxes, other than income taxes									30,832	29,230	32,702
Total expenses									286,522	265,832	300,848
Operating income									39,156	42,873	44,669
Allowance for equity funds used during construction									1,033	901	683
Equity in earnings of subsidiaries									0	0	0
Interest expense and other charges, net									(9,644)	(9,536)	(9,779)
Allowance for borrowed funds used during construction									451	366	275
Income before income taxes									30,996	34,604	35,848
Income taxes									12,704	13,087	13,302
Net income (loss)									18,292	21,517	22,546
Preferred stock dividends of subsidiaries									381	381	381
Net income attributable to Hawaiian Electric									17,911	21,136	22,165
Preferred stock dividends of Hawaiian Electric									0	0	0
Net income for common stock									17,911	21,136	22,165
Other subsidiaries
Revenues									0	0	0
Expenses
Fuel oil									0	0	0
Purchased power									0	0	0
Other operation and maintenance									0	0	0
Depreciation									0	0	0
Taxes, other than income taxes									0	0	0
Total expenses									0	0	0
Operating income									0	0	0
Allowance for equity funds used during construction									0	0	0
Equity in earnings of subsidiaries									0	0	0
Interest expense and other charges, net									0		0
Allowance for borrowed funds used during construction									0	0	0
Income before income taxes									0	0	0
Income taxes									0	0	0
Net income (loss)									0	0	0
Preferred stock dividends of subsidiaries									0	0	0
Net income attributable to Hawaiian Electric									0	0	0
Preferred stock dividends of Hawaiian Electric									0	0	0
Net income for common stock									0	0	0
Consolidating adjustments
Revenues									(83)	(106)	(81)
Expenses
Fuel oil									0	0	0
Purchased power									0	0	0
Other operation and maintenance									0	0	0
Depreciation									0	0	0
Taxes, other than income taxes									0	0	0
Total expenses									0	0	0
Operating income									(83)	(106)	(81)
Allowance for equity funds used during construction									0	0	0
Equity in earnings of subsidiaries									(38,057)	(42,391)	(42,920)
Interest expense and other charges, net									83	106	81
Allowance for borrowed funds used during construction									0	0	0
Income before income taxes									(38,057)	(42,391)	(42,920)
Income taxes									0	0	0
Net income (loss)									(38,057)	(42,391)	(42,920)
Preferred stock dividends of subsidiaries									0	0	0
Net income attributable to Hawaiian Electric									(38,057)	(42,391)	(42,920)
Preferred stock dividends of Hawaiian Electric									0	0	0
Net income for common stock									(38,057)	(42,391)	(42,920)
HECO Consolidated
Revenues	583,311	598,769	556,875	518,611	544,668	572,253	495,395	482,052	2,257,566	2,094,368	2,335,166
Expenses
Fuel oil									587,768	454,704	654,600
Purchased power									586,634	562,740	594,096
Other operation and maintenance									417,910	405,533	413,089
Depreciation									192,784	187,061	177,380
Taxes, other than income taxes									214,949	199,862	221,885
Total expenses									2,000,045	1,809,900	2,061,050
Operating income	66,460	87,076	55,047	48,938	68,644	89,812	70,686	55,326	257,521	284,468	274,116
Allowance for equity funds used during construction									12,483	8,325	6,928
Equity in earnings of subsidiaries									0	0	0
Interest expense and other charges, net									(69,637)	(66,824)	(66,370)
Allowance for borrowed funds used during construction									4,778	3,144	2,457
Income before income taxes									205,145	229,113	217,131
Income taxes									83,199	84,801	79,422
Net income (loss)	25,854	47,985	26,143	21,964	34,618	47,472	36,356	25,866	121,946	144,312	137,709
Preferred stock dividends of subsidiaries									915	915	915
Net income attributable to Hawaiian Electric									121,031	143,397	136,794
Preferred stock dividends of Hawaiian Electric									1,080	1,080	1,080
Net income for common stock	$ 25,355	$ 47,487	$ 25,644	$ 21,465	$ 34,119	$ 46,974	$ 35,857	$ 25,367	$ 119,951	$ 142,317	$ 135,714