Electric utility segment - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Utility property, plant and equipment
Total property, plant and equipment, net	$ 5,232,177				$ 5,109,628
Current assets
Cash and cash equivalents	193,126				196,813	$ 176,988
Restricted cash	21,881				30,872	0
Other long-term assets
Operating lease right-of-use assets	169,062				199,171
Total assets	14,542,361			$ 13,745,251	13,745,251
Capitalization
Total shareholders’ equity	2,323,231	$ 2,291,398		2,280,260	2,280,260	2,242,689	$ 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	34,271				24,941
Deferred credits and other liabilities
Deferred income taxes	376,356			379,324	379,324
Total liabilities and shareholders’ equity	14,542,361			$ 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	(606,411)				(591,969)
Current assets
Cash and cash equivalents	0				0
Restricted cash	0				0
Advances to affiliates	(28,500)				(35,700)
Customer accounts receivable, net	0				0
Accrued unbilled revenues, net	0				0
Other accounts receivable, net	(16,620)				(10,695)
Fuel oil stock, at average cost	0				0
Materials and supplies, at average cost	0				0
Prepayments and other	(321)				0
Regulatory assets	0				0
Total current assets	(45,441)				(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	(651,852)				(638,364)
Capitalization
Total shareholders’ equity	(606,411)				(591,969)	(588,886)			(576,838)
Cumulative preferred stock—not subject to mandatory redemption	0				0
Long-term debt, net	0				0
Total capitalization	(606,411)				(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	(28,500)				(35,700)
Accounts payable	0				0
Interest and preferred dividends payable	(40)				(46)
Taxes accrued, including revenue taxes	(321)				0
Regulatory liabilities	0				0
Other	(16,580)				(10,649)
Total current liabilities	(45,441)				(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	(651,852)				(638,364)
Hawaiian Electric (parent only) | Reportable Legal Entities
Utility property, plant and equipment
Land	42,389				42,598
Plant and equipment	4,910,344				4,765,362
Less accumulated depreciation	(1,656,533)				(1,591,241)
Construction in progress	163,757				165,137
Utility property, plant and equipment, net	3,459,957				3,381,856
Nonutility property, plant and equipment, less accumulated depreciation	5,307				5,310
Total property, plant and equipment, net	3,465,264				3,387,166
Investment in wholly owned subsidiaries, at equity	606,411				591,969
Current assets
Cash and cash equivalents	23,525				2,239
Restricted cash	20,458				30,749
Advances to affiliates	28,500				27,700
Customer accounts receivable, net	95,884				105,454
Accrued unbilled revenues, net	77,981				83,148
Other accounts receivable, net	18,878				18,396
Fuel oil stock, at average cost	38,716				69,003
Materials and supplies, at average cost	39,549				34,876
Prepayments and other	30,400				88,334
Regulatory assets	19,095				27,689
Total current assets	392,986				487,588
Other long-term assets
Operating lease right-of-use assets	142,912				174,886
Regulatory assets	453,384				476,390
Other	87,024				69,010
Total other long-term assets	683,320				720,286
Total assets	5,147,981				5,187,009
Capitalization
Total shareholders’ equity	2,093,398				2,047,352	1,993,254			1,957,641
Cumulative preferred stock—not subject to mandatory redemption	22,293				22,293
Long-term debt, net	1,116,305				1,006,737
Total capitalization	3,231,996				3,076,382
Current liabilities
Current portion of operating lease liabilities	64,776				63,582
Current portion of long-term debt	0				61,958
Short-term borrowings from non-affiliates	49,948				88,987
Short-term borrowings from affiliate	0				8,000
Accounts payable	88,867				139,056
Interest and preferred dividends payable	21,681				14,759
Taxes accrued, including revenue taxes	127,948				143,522
Regulatory liabilities	22,943				13,363
Other	57,763				51,295
Total current liabilities	433,926				584,522
Deferred credits and other liabilities
Operating lease liabilities	84,471				111,598
Deferred income taxes	269,635				265,864
Regulatory liabilities	661,649				664,894
Unamortized tax credits	83,626				86,852
Defined benefit pension and other postretirement benefit plans liability	321,768				339,471
Other	60,910				57,426
Total deferred credits and other liabilities	1,482,059				1,526,105
Total liabilities and shareholders’ equity	5,147,981				5,187,009
HELCO | Reportable Legal Entities
Utility property, plant and equipment
Land	5,606				5,606
Plant and equipment	1,331,934				1,313,727
Less accumulated depreciation	(592,461)				(574,615)
Construction in progress	20,975				9,993
Utility property, plant and equipment, net	766,054				754,711
Nonutility property, plant and equipment, less accumulated depreciation	115				114
Total property, plant and equipment, net	766,169				754,825
Investment in wholly owned subsidiaries, at equity	0				0
Current assets
Cash and cash equivalents	4,363				6,885
Restricted cash	0				123
Advances to affiliates	0				8,000
Customer accounts receivable, net	23,322				24,520
Accrued unbilled revenues, net	14,633				17,071
Other accounts receivable, net	2,625				1,907
Fuel oil stock, at average cost	10,216				8,901
Materials and supplies, at average cost	10,954				8,313
Prepayments and other	4,056				3,725
Regulatory assets	2,502				1,641
Total current assets	72,671				81,086
Other long-term assets
Operating lease right-of-use assets	1,466				1,537
Regulatory assets	103,556				109,163
Other	17,515				15,493
Total other long-term assets	122,537				126,193
Total assets	961,377				962,104
Capitalization
Total shareholders’ equity	308,066				298,998	303,345			295,874
Cumulative preferred stock—not subject to mandatory redemption	7,000				7,000
Long-term debt, net	216,424				206,416
Total capitalization	531,490				512,414
Current liabilities
Current portion of operating lease liabilities	98				94
Current portion of long-term debt	0				13,995
Short-term borrowings from non-affiliates	0				0
Short-term borrowings from affiliate	26,500				0
Accounts payable	13,730				25,629
Interest and preferred dividends payable	3,950				3,115
Taxes accrued, including revenue taxes	29,187				32,541
Regulatory liabilities	9,304				9,454
Other	14,285				11,362
Total current liabilities	97,054				96,190
Deferred credits and other liabilities
Operating lease liabilities	1,369				1,442
Deferred income taxes	52,682				53,534
Regulatory liabilities	174,919				178,474
Unamortized tax credits	15,502				16,196
Defined benefit pension and other postretirement benefit plans liability	66,237				69,928
Other	22,124				33,926
Total deferred credits and other liabilities	332,833				353,500
Total liabilities and shareholders’ equity	961,377				962,104
Maui Electric | Reportable Legal Entities
Utility property, plant and equipment
Land	3,594				3,612
Plant and equipment	1,180,630				1,161,199
Less accumulated depreciation	(540,923)				(524,301)
Construction in progress	27,805				17,944
Utility property, plant and equipment, net	671,106				658,454
Nonutility property, plant and equipment, less accumulated depreciation	1,532				1,532
Total property, plant and equipment, net	672,638				659,986
Investment in wholly owned subsidiaries, at equity	0				0
Current assets
Cash and cash equivalents	1,835				1,797
Restricted cash	0				0
Advances to affiliates	0				0
Customer accounts receivable, net	18,730				22,816
Accrued unbilled revenues, net	13,801				17,008
Other accounts receivable, net	2,191				1,960
Fuel oil stock, at average cost	11,511				14,033
Materials and supplies, at average cost	18,291				17,513
Prepayments and other	5,509				24,921
Regulatory assets	3,865				1,380
Total current assets	75,733				101,428
Other long-term assets
Operating lease right-of-use assets	362				386
Regulatory assets	95,281				98,817
Other	20,707				17,215
Total other long-term assets	116,350				116,418
Total assets	864,721				877,832
Capitalization
Total shareholders’ equity	298,268				292,870	285,440			280,863
Cumulative preferred stock—not subject to mandatory redemption	5,000				5,000
Long-term debt, net	228,399				188,561
Total capitalization	531,667				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	2,000				27,700
Accounts payable	15,883				23,085
Interest and preferred dividends payable	4,653				2,900
Taxes accrued, including revenue taxes	26,930				31,929
Regulatory liabilities	4,308				7,907
Other	19,582				15,297
Total current liabilities	73,388				128,849
Deferred credits and other liabilities
Operating lease liabilities	335				360
Deferred income taxes	59,218				57,752
Regulatory liabilities	94,723				98,218
Unamortized tax credits	14,388				14,820
Defined benefit pension and other postretirement benefit plans liability	66,145				69,364
Other	24,857				22,038
Total deferred credits and other liabilities	259,666				262,552
Total liabilities and shareholders’ equity	864,721				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	77				101
Restricted cash	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	77				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	77				101
Capitalization
Total shareholders’ equity	77				101	101			101
Cumulative preferred stock—not subject to mandatory redemption	0				0
Long-term debt, net	0				0
Total capitalization	77				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, including revenue taxes	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	77				101
Hawaiian Electric Company, Inc. and Subsidiaries
Utility property, plant and equipment
Land	51,589				51,816
Plant and equipment	7,422,908				7,240,288
Less accumulated depreciation	(2,789,917)				(2,690,157)
Construction in progress	212,537				193,074
Utility property, plant and equipment, net	4,897,117				4,795,021
Nonutility property, plant and equipment, less accumulated depreciation	6,954				6,956
Total property, plant and equipment, net	4,904,071				4,801,977
Investment in wholly owned subsidiaries, at equity	0				0
Current assets
Cash and cash equivalents	29,800				11,022	32,507
Restricted cash	20,458				30,872	0
Advances to affiliates	0				0
Customer accounts receivable, net	137,936				152,790
Accrued unbilled revenues, net	106,415				117,227
Other accounts receivable, net	7,074				11,568
Fuel oil stock, at average cost	60,443				91,937
Materials and supplies, at average cost	68,794				60,702
Prepayments and other	39,644				116,980
Regulatory assets	25,462				30,710
Total current assets	496,026				623,808
Other long-term assets
Operating lease right-of-use assets	144,740				176,809
Regulatory assets	652,221				684,370
Other	125,246				101,718
Total other long-term assets	922,207				962,897
Total assets	6,322,304				6,388,682
Capitalization
Total shareholders’ equity	2,093,398	$ 2,060,069	$ 2,044,499		2,047,352	$ 1,993,254	$ 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	1,561,128				1,401,714
Total capitalization	3,688,819				3,483,359
Current liabilities
Current portion of operating lease liabilities	64,906				63,707
Current portion of long-term debt	0				95,953
Short-term borrowings from non-affiliates	49,948				88,987
Short-term borrowings from affiliate	0				0
Accounts payable	118,480				187,770
Interest and preferred dividends payable	30,244				20,728
Taxes accrued, including revenue taxes	183,744				207,992
Regulatory liabilities	36,555				30,724
Other	75,050				67,305
Total current liabilities	558,927				763,166
Deferred credits and other liabilities
Operating lease liabilities	86,175				113,400
Deferred income taxes	381,535				377,150
Regulatory liabilities	931,291				941,586
Unamortized tax credits	113,516				117,868
Defined benefit pension and other postretirement benefit plans liability	454,150				478,763
Other	107,891				113,390
Total deferred credits and other liabilities	2,074,558				2,142,157
Total liabilities and shareholders’ equity	$ 6,322,304				$ 6,388,682