Electric utility segment - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Utility property, plant and equipment
Total property, plant and equipment, net	$ 5,181,427			$ 5,109,628
Current assets
Cash and Cash Equivalents, at Carrying Value	574,482			196,813	$ 198,549
Restricted Cash and Cash Equivalents	29,376			30,872	0
Other long-term assets
Operating lease right-of-use assets	184,759			199,171
Total assets	14,480,700		$ 13,745,251	13,745,251
Capitalization
Total shareholders’ equity	2,291,398		2,280,260	2,280,260	2,208,586	$ 2,183,515	$ 2,162,280
Cumulative preferred stock—not subject to mandatory redemption	0			0
Current liabilities
Interest and preferred dividends payable	24,396			24,941
Deferred credits and other liabilities
Deferred income taxes	368,834		379,324	379,324
Total liabilities and shareholders’ equity	14,480,700		$ 13,745,251	13,745,251
Consolidating adjustments
Utility property, plant and equipment
Land	0			0
Plant and equipment	0			0
Less accumulated depreciation	0			0
Construction in progress	0			0
Utility property, plant and equipment, net	0			0
Nonutility property, plant and equipment, less accumulated depreciation	0			0
Total property, plant and equipment, net	0			0
Investment in wholly owned subsidiaries, at equity	(599,198)			(591,969)
Current assets
Cash and Cash Equivalents, at Carrying Value	0			0
Restricted Cash and Cash Equivalents	0			0
Advances to affiliates	(13,500)			(35,700)
Customer accounts receivable, net	0			0
Accrued unbilled revenues, net	0			0
Other accounts receivable, net	(16,944)			(10,695)
Fuel oil stock, at average cost	0			0
Materials and supplies, at average cost	0			0
Prepayments and other	0			0
Regulatory assets	0			0
Total current assets	(30,444)			(46,395)
Other long-term assets
Operating lease right-of-use assets	0			0
Regulatory assets	0			0
Other	0			0
Total other long-term assets	0			0
Total assets	(629,642)			(638,364)
Capitalization
Total shareholders’ equity	(599,198)			(591,969)	(584,149)		(576,838)
Cumulative preferred stock—not subject to mandatory redemption	0			0
Long-term debt, net	0			0
Total capitalization	(599,198)			(591,969)
Current liabilities
Current portion of operating lease liabilities	0			0
Current portion of long-term debt	0			0
Short-term borrowings from non-affiliates	0			0
Short-term borrowings from affiliate	(13,500)			(35,700)
Accounts payable	0			0
Interest and preferred dividends payable	(6)			(46)
Taxes accrued	0			0
Regulatory liabilities	0			0
Other	(16,938)			(10,649)
Total current liabilities	(30,444)			(46,395)
Deferred credits and other liabilities
Operating lease liabilities	0			0
Deferred income taxes	0			0
Regulatory liabilities	0			0
Unamortized tax credits	0			0
Defined benefit pension and other postretirement benefit plans liability	0			0
Other	0			0
Total deferred credits and other liabilities	0			0
Total liabilities and shareholders’ equity	(629,642)			(638,364)
Hawaiian Electric (parent only) | Reportable Legal Entities
Utility property, plant and equipment
Land	42,389			42,598
Plant and equipment	4,859,373			4,765,362
Less accumulated depreciation	(1,636,504)			(1,591,241)
Construction in progress	170,655			165,137
Utility property, plant and equipment, net	3,435,913			3,381,856
Nonutility property, plant and equipment, less accumulated depreciation	5,308			5,310
Total property, plant and equipment, net	3,441,221			3,387,166
Investment in wholly owned subsidiaries, at equity	599,198			591,969
Current assets
Cash and Cash Equivalents, at Carrying Value	55,170			2,239
Restricted Cash and Cash Equivalents	29,376			30,749
Advances to affiliates	13,500			27,700
Customer accounts receivable, net	97,615			105,454
Accrued unbilled revenues, net	74,086			83,148
Other accounts receivable, net	19,409			18,396
Fuel oil stock, at average cost	30,477			69,003
Materials and supplies, at average cost	38,475			34,876
Prepayments and other	18,005			88,334
Regulatory assets	16,846			27,689
Total current assets	392,959			487,588
Other long-term assets
Operating lease right-of-use assets	159,169			174,886
Regulatory assets	460,493			476,390
Other	76,482			69,010
Total other long-term assets	696,144			720,286
Total assets	5,129,522			5,187,009
Capitalization
Total shareholders’ equity	2,060,069			2,047,352	1,971,762		1,957,641
Cumulative preferred stock—not subject to mandatory redemption	22,293			22,293
Long-term debt, net	1,116,186			1,006,737
Total capitalization	3,198,548			3,076,382
Current liabilities
Current portion of operating lease liabilities	64,405			63,582
Current portion of long-term debt	0			61,958
Short-term borrowings from non-affiliates	49,919			88,987
Short-term borrowings from affiliate	0			8,000
Accounts payable	79,071			139,056
Interest and preferred dividends payable	14,580			14,759
Taxes accrued	133,321			143,522
Regulatory liabilities	11,467			13,363
Other	55,378			51,295
Total current liabilities	408,141			584,522
Deferred credits and other liabilities
Operating lease liabilities	100,833			111,598
Deferred income taxes	261,044			265,864
Regulatory liabilities	674,621			664,894
Unamortized tax credits	84,885			86,852
Defined benefit pension and other postretirement benefit plans liability	340,672			339,471
Other	60,778			57,426
Total deferred credits and other liabilities	1,522,833			1,526,105
Total liabilities and shareholders’ equity	5,129,522			5,187,009
HELCO | Reportable Legal Entities
Utility property, plant and equipment
Land	5,606			5,606
Plant and equipment	1,321,091			1,313,727
Less accumulated depreciation	(586,351)			(574,615)
Construction in progress	20,181			9,993
Utility property, plant and equipment, net	760,527			754,711
Nonutility property, plant and equipment, less accumulated depreciation	115			114
Total property, plant and equipment, net	760,642			754,825
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and Cash Equivalents, at Carrying Value	4,594			6,885
Restricted Cash and Cash Equivalents	0			123
Advances to affiliates	0			8,000
Customer accounts receivable, net	21,422			24,520
Accrued unbilled revenues, net	12,705			17,071
Other accounts receivable, net	3,592			1,907
Fuel oil stock, at average cost	14,965			8,901
Materials and supplies, at average cost	10,116			8,313
Prepayments and other	17,151			3,725
Regulatory assets	2,598			1,641
Total current assets	87,143			81,086
Other long-term assets
Operating lease right-of-use assets	1,490			1,537
Regulatory assets	104,707			109,163
Other	16,915			15,493
Total other long-term assets	123,112			126,193
Total assets	970,897			962,104
Capitalization
Total shareholders’ equity	304,088			298,998	300,619		295,874
Cumulative preferred stock—not subject to mandatory redemption	7,000			7,000
Long-term debt, net	216,400			206,416
Total capitalization	527,488			512,414
Current liabilities
Current portion of operating lease liabilities	97			94
Current portion of long-term debt	14,000			13,995
Short-term borrowings from non-affiliates	0			0
Short-term borrowings from affiliate	12,000			0
Accounts payable	14,408			25,629
Interest and preferred dividends payable	3,349			3,115
Taxes accrued	32,526			32,541
Regulatory liabilities	7,401			9,454
Other	17,181			11,362
Total current liabilities	100,962			96,190
Deferred credits and other liabilities
Operating lease liabilities	1,394			1,442
Deferred income taxes	52,485			53,534
Regulatory liabilities	178,861			178,474
Unamortized tax credits	15,773			16,196
Defined benefit pension and other postretirement benefit plans liability	69,719			69,928
Other	24,215			33,926
Total deferred credits and other liabilities	342,447			353,500
Total liabilities and shareholders’ equity	970,897			962,104
Maui Electric | Reportable Legal Entities
Utility property, plant and equipment
Land	3,612			3,612
Plant and equipment	1,173,377			1,161,199
Less accumulated depreciation	(535,689)			(524,301)
Construction in progress	23,651			17,944
Utility property, plant and equipment, net	664,951			658,454
Nonutility property, plant and equipment, less accumulated depreciation	1,532			1,532
Total property, plant and equipment, net	666,483			659,986
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and Cash Equivalents, at Carrying Value	4,130			1,797
Restricted Cash and Cash Equivalents	0			0
Advances to affiliates	0			0
Customer accounts receivable, net	19,001			22,816
Accrued unbilled revenues, net	13,810			17,008
Other accounts receivable, net	4,358			1,960
Fuel oil stock, at average cost	15,037			14,033
Materials and supplies, at average cost	17,653			17,513
Prepayments and other	2,773			24,921
Regulatory assets	1,842			1,380
Total current assets	78,604			101,428
Other long-term assets
Operating lease right-of-use assets	370			386
Regulatory assets	96,084			98,817
Other	19,588			17,215
Total other long-term assets	116,042			116,418
Total assets	861,129			877,832
Capitalization
Total shareholders’ equity	295,009			292,870	283,429		280,863
Cumulative preferred stock—not subject to mandatory redemption	5,000			5,000
Long-term debt, net	228,369			188,561
Total capitalization	528,378			486,431
Current liabilities
Current portion of operating lease liabilities	32			31
Current portion of long-term debt	0			20,000
Short-term borrowings from non-affiliates	0			0
Short-term borrowings from affiliate	1,500			27,700
Accounts payable	13,599			23,085
Interest and preferred dividends payable	2,736			2,900
Taxes accrued	28,004			31,929
Regulatory liabilities	7,199			7,907
Other	16,070			15,297
Total current liabilities	69,140			128,849
Deferred credits and other liabilities
Operating lease liabilities	343			360
Deferred income taxes	57,523			57,752
Regulatory liabilities	98,231			98,218
Unamortized tax credits	14,348			14,820
Defined benefit pension and other postretirement benefit plans liability	69,459			69,364
Other	23,707			22,038
Total deferred credits and other liabilities	263,611			262,552
Total liabilities and shareholders’ equity	861,129			877,832
Other subsidiaries | Reportable Legal Entities
Utility property, plant and equipment
Land	0			0
Plant and equipment	0			0
Less accumulated depreciation	0			0
Construction in progress	0			0
Utility property, plant and equipment, net	0			0
Nonutility property, plant and equipment, less accumulated depreciation	0			0
Total property, plant and equipment, net	0			0
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and Cash Equivalents, at Carrying Value	101			101
Restricted Cash and Cash Equivalents	0			0
Advances to affiliates	0			0
Customer accounts receivable, net	0			0
Accrued unbilled revenues, net	0			0
Other accounts receivable, net	0			0
Fuel oil stock, at average cost	0			0
Materials and supplies, at average cost	0			0
Prepayments and other	0			0
Regulatory assets	0			0
Total current assets	101			101
Other long-term assets
Operating lease right-of-use assets	0			0
Regulatory assets	0			0
Other	0			0
Total other long-term assets	0			0
Total assets	101			101
Capitalization
Total shareholders’ equity	101			101	101		101
Cumulative preferred stock—not subject to mandatory redemption	0			0
Long-term debt, net	0			0
Total capitalization	101			101
Current liabilities
Current portion of operating lease liabilities	0			0
Current portion of long-term debt	0			0
Short-term borrowings from non-affiliates	0			0
Short-term borrowings from affiliate	0			0
Accounts payable	0			0
Interest and preferred dividends payable	0			0
Taxes accrued	0			0
Regulatory liabilities	0			0
Other	0			0
Total current liabilities	0			0
Deferred credits and other liabilities
Operating lease liabilities	0			0
Deferred income taxes	0			0
Regulatory liabilities	0			0
Unamortized tax credits	0			0
Defined benefit pension and other postretirement benefit plans liability	0			0
Other	0			0
Total deferred credits and other liabilities	0			0
Total liabilities and shareholders’ equity	101			101
Hawaiian Electric Company, Inc. and Subsidiaries
Utility property, plant and equipment
Land	51,607			51,816
Plant and equipment	7,353,841			7,240,288
Less accumulated depreciation	(2,758,544)			(2,690,157)
Construction in progress	214,487			193,074
Utility property, plant and equipment, net	4,861,391			4,795,021
Nonutility property, plant and equipment, less accumulated depreciation	6,955			6,956
Total property, plant and equipment, net	4,868,346			4,801,977
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and Cash Equivalents, at Carrying Value	63,995			11,022	23,361
Restricted Cash and Cash Equivalents	29,376			30,872	0
Advances to affiliates	0			0
Customer accounts receivable, net	138,038			152,790
Accrued unbilled revenues, net	100,601			117,227
Other accounts receivable, net	10,415			11,568
Fuel oil stock, at average cost	60,479			91,937
Materials and supplies, at average cost	66,244			60,702
Prepayments and other	37,929			116,980
Regulatory assets	21,286			30,710
Total current assets	528,363			623,808
Other long-term assets
Operating lease right-of-use assets	161,029			176,809
Regulatory assets	661,284			684,370
Other	112,985			101,718
Total other long-term assets	935,298			962,897
Total assets	6,332,007			6,388,682
Capitalization
Total shareholders’ equity	2,060,069	$ 2,044,499		2,047,352	$ 1,971,762	$ 1,964,478	$ 1,957,641
Cumulative preferred stock—not subject to mandatory redemption	34,293			34,293
Long-term debt, net	1,560,955			1,401,714
Total capitalization	3,655,317			3,483,359
Current liabilities
Current portion of operating lease liabilities	64,534			63,707
Current portion of long-term debt	14,000			95,953
Short-term borrowings from non-affiliates	49,919			88,987
Short-term borrowings from affiliate	0			0
Accounts payable	107,078			187,770
Interest and preferred dividends payable	20,659			20,728
Taxes accrued	193,851			207,992
Regulatory liabilities	26,067			30,724
Other	71,691			67,305
Total current liabilities	547,799			763,166
Deferred credits and other liabilities
Operating lease liabilities	102,570			113,400
Deferred income taxes	371,052			377,150
Regulatory liabilities	951,713			941,586
Unamortized tax credits	115,006			117,868
Defined benefit pension and other postretirement benefit plans liability	479,850			478,763
Other	108,700			113,390
Total deferred credits and other liabilities	2,128,891			2,142,157
Total liabilities and shareholders’ equity	$ 6,332,007			$ 6,388,682