Electric utility segment - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Utility property, plant and equipment
Total property, plant and equipment, net	$ 5,335,130			$ 5,265,735
Current assets
Cash and cash equivalents	227,923			341,421	$ 193,126
Restricted cash	9,412			17,558	21,881
Other long-term assets
Operating lease right-of-use assets	141,816			153,069
Total assets	15,760,163			15,004,007
Capitalization
Common stock equity	2,383,543	$ 2,367,329	$ 2,321,293	2,337,502	2,323,231	$ 2,291,398	$ 2,276,505	$ 2,280,260
Preferred stock of subsidiaries - not subject to mandatory redemption	34,293			34,293
Current liabilities
Interest and preferred dividends payable	33,307			23,547
Deferred credits and other liabilities
Deferred income taxes	378,139			395,089
Total liabilities and shareholders’ equity	15,760,163			15,004,007
Hawaiian Electric Consolidated
Utility property, plant and equipment
Land	51,610			51,611
Plant and equipment	7,669,720			7,509,343
Less accumulated depreciation	(2,947,715)			(2,819,079)
Construction in progress	221,518			188,342
Utility property, plant and equipment, net	4,995,133			4,930,217
Nonutility property, plant and equipment, less accumulated depreciation	6,950			6,953
Total property, plant and equipment, net	5,002,083			4,937,170
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and cash equivalents	36,467			47,360	29,800
Restricted cash	6,313			15,966	20,458
Advances to affiliates	0			0
Customer accounts receivable, net	174,237			147,832
Accrued unbilled revenues, net	129,079			101,036
Other accounts receivable, net	6,116			7,673
Fuel oil stock, at average cost	100,801			58,238
Materials and supplies, at average cost	72,997			67,344
Prepayments and other	53,961			44,083
Regulatory assets	56,224			30,435
Total current assets	636,195			519,967
Other long-term assets
Operating lease right-of-use assets	119,624			127,654
Regulatory assets	700,980			736,273
Other	144,026			136,309
Total other long-term assets	964,630			1,000,236
Total assets	6,602,908			6,457,373
Capitalization
Common stock equity	2,193,919	$ 2,171,396	$ 2,157,385	2,141,918	2,093,398	$ 2,060,069	$ 2,044,499	2,047,352
Preferred stock of subsidiaries - not subject to mandatory redemption	34,293			34,293
Long-term debt, net	1,676,223			1,561,302
Total capitalization	3,904,435			3,737,513
Current liabilities
Current portion of operating lease liabilities	64,894			64,730
Short-term borrowings from non-affiliates	0			49,979
Short-term borrowings from affiliate	0			0
Accounts payable	146,875			133,849
Interest and preferred dividends payable	28,610			20,350
Taxes accrued, including revenue taxes	196,368			192,524
Regulatory liabilities	32,261			37,301
Other	84,506			74,262
Total current liabilities	553,514			572,995
Deferred credits and other liabilities
Operating lease liabilities	67,802			69,494
Deferred income taxes	396,553			397,798
Regulatory liabilities	943,251			922,485
Unamortized tax credits	106,378			111,915
Defined benefit pension and other postretirement benefit plans liability	509,972			530,532
Other	121,003			114,641
Total deferred credits and other liabilities	2,144,959			2,146,865
Total liabilities and shareholders’ equity	6,602,908			6,457,373
Hawaiian Electric Consolidated | Reportable Legal Entities | Hawaiian Electric Industries, Inc.
Utility property, plant and equipment
Land	42,410			42,411
Plant and equipment	5,063,487			4,960,470
Less accumulated depreciation	(1,766,707)			(1,677,256)
Construction in progress	172,417			143,616
Utility property, plant and equipment, net	3,511,607			3,469,241
Nonutility property, plant and equipment, less accumulated depreciation	5,303			5,306
Total property, plant and equipment, net	3,516,910			3,474,547
Investment in wholly owned subsidiaries, at equity	639,900			626,890
Current assets
Cash and cash equivalents	25,981			42,205	23,525
Restricted cash	6,313			15,966	20,458
Advances to affiliates	700			26,700
Customer accounts receivable, net	118,776			102,736
Accrued unbilled revenues, net	93,949			73,628
Other accounts receivable, net	20,732			17,984
Fuel oil stock, at average cost	71,072			38,777
Materials and supplies, at average cost	43,094			38,786
Prepayments and other	41,706			34,306
Regulatory assets	47,004			22,095
Total current assets	469,327			413,183
Other long-term assets
Operating lease right-of-use assets	96,026			125,858
Regulatory assets	489,746			513,192
Other	112,298			98,307
Total other long-term assets	698,070			737,357
Total assets	5,324,207			5,251,977
Capitalization
Common stock equity	2,193,919			2,141,918	2,093,398			2,047,352
Preferred stock of subsidiaries - not subject to mandatory redemption	22,293			22,293
Long-term debt, net	1,176,477			1,116,426
Total capitalization	3,392,689			3,280,637
Current liabilities
Current portion of operating lease liabilities	61,505			64,599
Short-term borrowings from non-affiliates				49,979
Short-term borrowings from affiliate	0			0
Accounts payable	101,685			97,102
Interest and preferred dividends payable	20,390			14,480
Taxes accrued, including revenue taxes	136,016			135,018
Regulatory liabilities	21,257			20,224
Other	71,738			57,926
Total current liabilities	412,591			439,328
Deferred credits and other liabilities
Operating lease liabilities	47,585			67,824
Deferred income taxes	284,245			282,685
Regulatory liabilities	672,712			656,270
Unamortized tax credits	78,215			82,563
Defined benefit pension and other postretirement benefit plans liability	364,749			373,112
Other	71,421			69,558
Total deferred credits and other liabilities	1,518,927			1,532,012
Total liabilities and shareholders’ equity	5,324,207			5,251,977
Hawaiian Electric Consolidated | Reportable Legal Entities | Hawaii Electric Light
Utility property, plant and equipment
Land	5,606			5,606
Plant and equipment	1,375,782			1,352,885
Less accumulated depreciation	(619,003)			(597,606)
Construction in progress	17,966			13,043
Utility property, plant and equipment, net	780,351			773,928
Nonutility property, plant and equipment, less accumulated depreciation	115			115
Total property, plant and equipment, net	780,466			774,043
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and cash equivalents	3,788			3,046	4,363
Restricted cash	0			0	0
Advances to affiliates	0			0
Customer accounts receivable, net	29,371			23,989
Accrued unbilled revenues, net	17,660			13,631
Other accounts receivable, net	3,843			3,028
Fuel oil stock, at average cost	13,079			8,471
Materials and supplies, at average cost	10,107			9,896
Prepayments and other	5,232			5,197
Regulatory assets	2,966			1,954
Total current assets	86,046			69,212
Other long-term assets
Operating lease right-of-use assets	23,271			1,443
Regulatory assets	108,093			114,461
Other	19,008			17,992
Total other long-term assets	150,372			133,896
Total assets	1,016,884			977,151
Capitalization
Common stock equity	323,691			317,451	308,066			298,998
Preferred stock of subsidiaries - not subject to mandatory redemption	7,000			7,000
Long-term debt, net	246,360			216,447
Total capitalization	577,051			540,898
Current liabilities
Current portion of operating lease liabilities	3,354			98
Short-term borrowings from non-affiliates				0
Short-term borrowings from affiliate	700			18,800
Accounts payable	24,640			19,570
Interest and preferred dividends payable	3,750			3,138
Taxes accrued, including revenue taxes	31,338			29,869
Regulatory liabilities	4,164			8,785
Other	14,488			13,851
Total current liabilities	82,434			94,111
Deferred credits and other liabilities
Operating lease liabilities	19,917			1,344
Deferred income taxes	51,822			54,108
Regulatory liabilities	177,877			173,938
Unamortized tax credits	14,577			15,363
Defined benefit pension and other postretirement benefit plans liability	74,183			77,679
Other	19,023			19,710
Total deferred credits and other liabilities	357,399			342,142
Total liabilities and shareholders’ equity	1,016,884			977,151
Hawaiian Electric Consolidated | Reportable Legal Entities | Maui Electric
Utility property, plant and equipment
Land	3,594			3,594
Plant and equipment	1,230,451			1,195,988
Less accumulated depreciation	(562,005)			(544,217)
Construction in progress	31,135			31,683
Utility property, plant and equipment, net	703,175			687,048
Nonutility property, plant and equipment, less accumulated depreciation	1,532			1,532
Total property, plant and equipment, net	704,707			688,580
Investment in wholly owned subsidiaries, at equity	0			0
Current assets
Cash and cash equivalents	6,621			2,032	1,835
Restricted cash	0			0	0
Advances to affiliates	0			0
Customer accounts receivable, net	26,090			21,107
Accrued unbilled revenues, net	17,470			13,777
Other accounts receivable, net	3,616			2,856
Fuel oil stock, at average cost	16,650			10,990
Materials and supplies, at average cost	19,796			18,662
Prepayments and other	7,023			4,580
Regulatory assets	6,254			6,386
Total current assets	103,520			80,390
Other long-term assets
Operating lease right-of-use assets	327			353
Regulatory assets	103,141			108,620
Other	18,448			20,010
Total other long-term assets	121,916			128,983
Total assets	930,143			897,953
Capitalization
Common stock equity	316,132			309,363	298,268			292,870
Preferred stock of subsidiaries - not subject to mandatory redemption	5,000			5,000
Long-term debt, net	253,386			228,429
Total capitalization	574,518			542,792
Current liabilities
Current portion of operating lease liabilities	35			33
Short-term borrowings from non-affiliates				0
Short-term borrowings from affiliate	0			7,900
Accounts payable	20,550			17,177
Interest and preferred dividends payable	4,471			2,790
Taxes accrued, including revenue taxes	29,014			27,637
Regulatory liabilities	6,840			8,292
Other	20,503			18,621
Total current liabilities	81,413			82,450
Deferred credits and other liabilities
Operating lease liabilities	300			326
Deferred income taxes	60,486			61,005
Regulatory liabilities	92,662			92,277
Unamortized tax credits	13,586			13,989
Defined benefit pension and other postretirement benefit plans liability	76,619			79,741
Other	30,559			25,373
Total deferred credits and other liabilities	274,212			272,711
Total liabilities and shareholders’ equity	930,143			897,953
Hawaiian Electric Consolidated | Reportable Legal Entities | Other subsidiaries
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			77	77
Restricted cash	0			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			77
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			77
Capitalization
Common stock equity	77			77	77			101
Preferred stock of subsidiaries - not subject to mandatory redemption	0			0
Long-term debt, net	0			0
Total capitalization	77			77
Current liabilities
Current portion of operating lease liabilities	0			0
Short-term borrowings from non-affiliates				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			77
Hawaiian Electric Consolidated | 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	(639,900)			(626,890)
Current assets
Cash and cash equivalents	0			0	0
Restricted cash	0			0	0
Advances to affiliates	(700)			(26,700)
Customer accounts receivable, net	0			0
Accrued unbilled revenues, net	0			0
Other accounts receivable, net	(22,075)			(16,195)
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	(22,775)			(42,895)
Other long-term assets
Operating lease right-of-use assets	0			0
Regulatory assets	0			0
Other	(5,728)			0
Total other long-term assets	(5,728)			0
Total assets	(668,403)			(669,785)
Capitalization
Common stock equity	(639,900)			(626,891)	$ (606,411)			$ (591,969)
Preferred stock of subsidiaries - not subject to mandatory redemption	0			0
Long-term debt, net	0			0
Total capitalization	(639,900)			(626,891)
Current liabilities
Current portion of operating lease liabilities	0			0
Short-term borrowings from non-affiliates				0
Short-term borrowings from affiliate	(700)			(26,700)
Accounts payable	0			0
Interest and preferred dividends payable	(1)			(58)
Taxes accrued, including revenue taxes	0			0
Regulatory liabilities	0			0
Other	(22,223)			(16,136)
Total current liabilities	(22,924)			(42,894)
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	(5,579)			0
Other	0			0
Total deferred credits and other liabilities	(5,579)			0
Total liabilities and shareholders’ equity	$ (668,403)			$ (669,785)