Electric utility segment - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Utility property, plant and equipment
Total property, plant and equipment, net	$ 5,150,385		$ 5,109,628
Current assets
Cash and Cash Equivalents, at Carrying Value	205,514		196,813	$ 186,407
Restricted Cash and Cash Equivalents	30,902		30,872	0
Other long-term assets
Operating lease right-of-use assets	200,842		199,171
Total assets	13,849,018	$ 13,745,251	13,745,251
Capitalization
Total shareholders’ equity	2,276,505	2,280,260	2,280,260	2,183,515	$ 2,162,280
Cumulative preferred stock—not subject to mandatory redemption	0		0
Current liabilities
Interest and preferred dividends payable	32,588		24,941
Deferred credits and other liabilities
Deferred income taxes	382,872	379,324	379,324
Total liabilities and shareholders’ equity	13,849,018	$ 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	(593,097)		(591,969)
Current assets
Cash and Cash Equivalents, at Carrying Value	0		0
Restricted Cash and Cash Equivalents	0		0
Advances to affiliates	(44,700)		(35,700)
Customer accounts receivable, net	0		0
Accrued unbilled revenues, net	0		0
Other accounts receivable, net	(11,269)		(10,695)
Fuel oil stock, at average cost	0		0
Materials and supplies, at average cost	0		0
Prepayments and other	(1,576)		0
Regulatory assets	0		0
Total current assets	(57,545)		(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	(650,642)		(638,364)
Capitalization
Total shareholders’ equity	(593,097)		(591,969)	(582,374)	(576,838)
Cumulative preferred stock—not subject to mandatory redemption	0		0
Long-term debt, net	0		0
Total capitalization	(593,097)		(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	(44,700)		(35,700)
Accounts payable	0		0
Interest and preferred dividends payable	(89)		(46)
Taxes accrued	(1,576)		0
Regulatory liabilities	0		0
Other	(11,180)		(10,649)
Total current liabilities	(57,545)		(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	(650,642)		(638,364)
Hawaiian Electric (parent only) | Reportable Legal Entities
Utility property, plant and equipment
Land	42,389		42,598
Plant and equipment	4,821,180		4,765,362
Less accumulated depreciation	(1,614,651)		(1,591,241)
Construction in progress	164,467		165,137
Utility property, plant and equipment, net	3,413,385		3,381,856
Nonutility property, plant and equipment, less accumulated depreciation	5,309		5,310
Total property, plant and equipment, net	3,418,694		3,387,166
Investment in wholly owned subsidiaries, at equity	593,097		591,969
Current assets
Cash and Cash Equivalents, at Carrying Value	4,589		2,239
Restricted Cash and Cash Equivalents	30,902		30,749
Advances to affiliates	44,700		27,700
Customer accounts receivable, net	113,999		105,454
Accrued unbilled revenues, net	81,468		83,148
Other accounts receivable, net	17,593		18,396
Fuel oil stock, at average cost	65,688		69,003
Materials and supplies, at average cost	35,006		34,876
Prepayments and other	28,445		88,334
Regulatory assets	25,490		27,689
Total current assets	447,880		487,588
Other long-term assets
Operating lease right-of-use assets	175,205		174,886
Regulatory assets	466,795		476,390
Other	73,796		69,010
Total other long-term assets	715,796		720,286
Total assets	5,175,467		5,187,009
Capitalization
Total shareholders’ equity	2,044,499		2,047,352	1,964,478	1,957,641
Cumulative preferred stock—not subject to mandatory redemption	22,293		22,293
Long-term debt, net	1,101,614		1,006,737
Total capitalization	3,168,406		3,076,382
Current liabilities
Current portion of operating lease liabilities	63,616		63,582
Current portion of long-term debt	0		61,958
Short-term borrowings from non-affiliates	99,956		88,987
Short-term borrowings from affiliate	0		8,000
Accounts payable	113,932		139,056
Interest and preferred dividends payable	20,095		14,759
Taxes accrued	109,383		143,522
Regulatory liabilities	19,762		13,363
Other	50,411		51,295
Total current liabilities	477,155		584,522
Deferred credits and other liabilities
Operating lease liabilities	117,183		111,598
Deferred income taxes	269,478		265,864
Regulatory liabilities	670,187		664,894
Unamortized tax credits	84,309		86,852
Defined benefit pension and other postretirement benefit plans liability	333,716		339,471
Other	55,033		57,426
Total deferred credits and other liabilities	1,529,906		1,526,105
Total liabilities and shareholders’ equity	5,175,467		5,187,009
HELCO | Reportable Legal Entities
Utility property, plant and equipment
Land	5,606		5,606
Plant and equipment	1,317,355		1,313,727
Less accumulated depreciation	(581,038)		(574,615)
Construction in progress	12,530		9,993
Utility property, plant and equipment, net	754,453		754,711
Nonutility property, plant and equipment, less accumulated depreciation	115		114
Total property, plant and equipment, net	754,568		754,825
Investment in wholly owned subsidiaries, at equity	0		0
Current assets
Cash and Cash Equivalents, at Carrying Value	4,654		6,885
Restricted Cash and Cash Equivalents	0		123
Advances to affiliates	0		8,000
Customer accounts receivable, net	23,327		24,520
Accrued unbilled revenues, net	16,468		17,071
Other accounts receivable, net	2,596		1,907
Fuel oil stock, at average cost	8,684		8,901
Materials and supplies, at average cost	9,153		8,313
Prepayments and other	3,816		3,725
Regulatory assets	1,928		1,641
Total current assets	70,626		81,086
Other long-term assets
Operating lease right-of-use assets	1,514		1,537
Regulatory assets	105,956		109,163
Other	17,316		15,493
Total other long-term assets	124,786		126,193
Total assets	949,980		962,104
Capitalization
Total shareholders’ equity	300,986		298,998	298,497	295,874
Cumulative preferred stock—not subject to mandatory redemption	7,000		7,000
Long-term debt, net	206,437		206,416
Total capitalization	514,423		512,414
Current liabilities
Current portion of operating lease liabilities	96		94
Current portion of long-term debt	13,997		13,995
Short-term borrowings from non-affiliates	0		0
Short-term borrowings from affiliate	2,500		0
Accounts payable	14,401		25,629
Interest and preferred dividends payable	3,806		3,115
Taxes accrued	26,846		32,541
Regulatory liabilities	12,813		9,454
Other	11,196		11,362
Total current liabilities	85,655		96,190
Deferred credits and other liabilities
Operating lease liabilities	1,418		1,442
Deferred income taxes	53,374		53,534
Regulatory liabilities	178,479		178,474
Unamortized tax credits	15,985		16,196
Defined benefit pension and other postretirement benefit plans liability	68,756		69,928
Other	31,890		33,926
Total deferred credits and other liabilities	349,902		353,500
Total liabilities and shareholders’ equity	949,980		962,104
Maui Electric | Reportable Legal Entities
Utility property, plant and equipment
Land	3,612		3,612
Plant and equipment	1,167,120		1,161,199
Less accumulated depreciation	(530,414)		(524,301)
Construction in progress	22,532		17,944
Utility property, plant and equipment, net	662,850		658,454
Nonutility property, plant and equipment, less accumulated depreciation	1,532		1,532
Total property, plant and equipment, net	664,382		659,986
Investment in wholly owned subsidiaries, at equity	0		0
Current assets
Cash and Cash Equivalents, at Carrying Value	3,065		1,797
Restricted Cash and Cash Equivalents	0		0
Advances to affiliates	0		0
Customer accounts receivable, net	21,354		22,816
Accrued unbilled revenues, net	15,844		17,008
Other accounts receivable, net	2,327		1,960
Fuel oil stock, at average cost	15,155		14,033
Materials and supplies, at average cost	17,039		17,513
Prepayments and other	5,222		24,921
Regulatory assets	1,549		1,380
Total current assets	81,555		101,428
Other long-term assets
Operating lease right-of-use assets	378		386
Regulatory assets	96,926		98,817
Other	17,781		17,215
Total other long-term assets	115,085		116,418
Total assets	861,022		877,832
Capitalization
Total shareholders’ equity	292,010		292,870	283,776	280,863
Cumulative preferred stock—not subject to mandatory redemption	5,000		5,000
Long-term debt, net	188,587		188,561
Total capitalization	485,597		486,431
Current liabilities
Current portion of operating lease liabilities	31		31
Current portion of long-term debt	0		20,000
Short-term borrowings from non-affiliates	0		0
Short-term borrowings from affiliate	42,200		27,700
Accounts payable	17,602		23,085
Interest and preferred dividends payable	4,129		2,900
Taxes accrued	24,338		31,929
Regulatory liabilities	10,136		7,907
Other	15,321		15,297
Total current liabilities	113,757		128,849
Deferred credits and other liabilities
Operating lease liabilities	352		360
Deferred income taxes	58,017		57,752
Regulatory liabilities	98,593		98,218
Unamortized tax credits	14,584		14,820
Defined benefit pension and other postretirement benefit plans liability	68,339		69,364
Other	21,783		22,038
Total deferred credits and other liabilities	261,668		262,552
Total liabilities and shareholders’ equity	861,022		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	7,305,655		7,240,288
Less accumulated depreciation	(2,726,103)		(2,690,157)
Construction in progress	199,529		193,074
Utility property, plant and equipment, net	4,830,688		4,795,021
Nonutility property, plant and equipment, less accumulated depreciation	6,956		6,956
Total property, plant and equipment, net	4,837,644		4,801,977
Investment in wholly owned subsidiaries, at equity	0		0
Current assets
Cash and Cash Equivalents, at Carrying Value	12,409		11,022	8,381
Restricted Cash and Cash Equivalents	30,902		30,872	0
Advances to affiliates	0		0
Customer accounts receivable, net	158,680		152,790
Accrued unbilled revenues, net	113,780		117,227
Other accounts receivable, net	11,247		11,568
Fuel oil stock, at average cost	89,527		91,937
Materials and supplies, at average cost	61,198		60,702
Prepayments and other	35,907		116,980
Regulatory assets	28,967		30,710
Total current assets	542,617		623,808
Other long-term assets
Operating lease right-of-use assets	177,097		176,809
Regulatory assets	669,677		684,370
Other	108,893		101,718
Total other long-term assets	955,667		962,897
Total assets	6,335,928		6,388,682
Capitalization
Total shareholders’ equity	2,044,499		2,047,352	$ 1,964,478	$ 1,957,641
Cumulative preferred stock—not subject to mandatory redemption	34,293		34,293
Long-term debt, net	1,496,638		1,401,714
Total capitalization	3,575,430		3,483,359
Current liabilities
Current portion of operating lease liabilities	63,743		63,707
Current portion of long-term debt	13,997		95,953
Short-term borrowings from non-affiliates	99,956		88,987
Short-term borrowings from affiliate	0		0
Accounts payable	145,935		187,770
Interest and preferred dividends payable	27,941		20,728
Taxes accrued	158,991		207,992
Regulatory liabilities	42,711		30,724
Other	65,748		67,305
Total current liabilities	619,022		763,166
Deferred credits and other liabilities
Operating lease liabilities	118,953		113,400
Deferred income taxes	380,869		377,150
Regulatory liabilities	947,259		941,586
Unamortized tax credits	114,878		117,868
Defined benefit pension and other postretirement benefit plans liability	470,811		478,763
Other	108,706		113,390
Total deferred credits and other liabilities	2,141,476		2,142,157
Total liabilities and shareholders’ equity	$ 6,335,928		$ 6,388,682