Electric utility segment - Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Utility property, plant and equipment
Total property, plant and equipment, net	$ 5,265,735		$ 5,109,628
Current assets
Cash and cash equivalents	341,421		196,813	$ 169,208
Other long-term assets
Operating lease right-of-use-assets	153,069		199,171
Total assets	15,004,007	$ 13,745,251	13,745,251	13,104,051
Capitalization
Common stock equity	2,337,502	2,280,260	2,280,260	2,162,280	$ 2,097,386
Cumulative preferred stock–not subject to mandatory redemption	0		0
Current liabilities
Current portion of operating lease liabilities	64,730		63,707
Interest and dividends payable	23,547		24,941
Deferred credits and other liabilities
Deferred income taxes	395,089	379,324	379,324
Total capitalization and liabilities	15,004,007	$ 13,745,251	13,745,251
Hawaiian Electric (parent only)
Utility property, plant and equipment
Total property, plant and equipment, net	2,456		2,931
Other long-term assets
Total assets	2,930,236		2,821,587
Capitalization
Common stock equity	2,337,502		2,280,260
Cumulative preferred stock–not subject to mandatory redemption	0		0
Current liabilities
Short-term borrowings from non-affiliate	14,909		0
Deferred credits and other liabilities
Total capitalization and liabilities	2,930,236		2,821,587
Hawaiian Electric Company, Inc. and Subsidiaries
Utility property, plant and equipment
Land	51,611		51,816
Plant and equipment	7,509,343		7,240,288
Less accumulated depreciation	(2,819,079)		(2,690,157)
Construction in progress	188,342		193,074
Utility property, plant and equipment, net	4,930,217		4,795,021
Nonutility property, plant and equipment, less accumulated depreciation	6,953		6,956
Total property, plant and equipment, net	4,937,170		4,801,977
Investment in wholly-owned subsidiaries, at equity	0		0
Current assets
Cash and cash equivalents	47,360		11,022	35,877
Restricted cash	15,966		30,872
Advances to affiliates	0		0
Customer accounts receivable, net	147,832		152,790
Accrued unbilled revenues, net	101,036		117,227
Other accounts receivable, net	7,673		11,568
Fuel oil stock, at average cost	58,238		91,937
Materials and supplies, at average cost	67,344		60,702
Prepayments and other	44,083		116,980
Regulatory assets	30,435		30,710
Total current assets	519,967		623,808
Other long-term assets
Operating lease right-of-use-assets	127,654		176,809
Regulatory assets	736,273		684,370
Other	136,309		101,718
Total other long-term assets	1,000,236		962,897
Total assets	6,457,373		6,388,682
Capitalization
Common stock equity	2,141,918		2,047,352	1,957,641	1,845,283
Cumulative preferred stock–not subject to mandatory redemption	34,293		34,293
Long-term debt, net	1,561,302		1,401,714
Total capitalization	3,737,513		3,483,359
Current liabilities
Current portion of operating lease liabilities	64,730		63,707
Current portion of long-term debt, net	0		95,953
Short-term borrowings from non-affiliate	49,979		88,987
Short-term borrowings-affiliate	0		0
Accounts payable	133,849		187,770
Interest and dividends payable	20,350		20,728
Taxes accrued, including revenue taxes	192,524		207,992
Regulatory liabilities	37,301		30,724
Other	74,262		67,305
Total current liabilities	572,995		763,166
Deferred credits and other liabilities
Operating lease liabilities	69,494		113,400
Deferred income taxes	397,798		377,150
Regulatory liabilities	922,485		941,586
Unamortized tax credits	111,915		117,868
Defined benefit pension and other postretirement benefit plans liability	530,532		478,763
Other	114,641		113,390
Total deferred credits and other liabilities	2,146,865		2,142,157
Total capitalization and liabilities	6,457,373		6,388,682
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Hawaiian Electric (parent only)
Utility property, plant and equipment
Land	42,411		42,598
Plant and equipment	4,960,470		4,765,362
Less accumulated depreciation	(1,677,256)		(1,591,241)
Construction in progress	143,616		165,137
Utility property, plant and equipment, net	3,469,241		3,381,856
Nonutility property, plant and equipment, less accumulated depreciation	5,306		5,310
Total property, plant and equipment, net	3,474,547		3,387,166
Investment in wholly-owned subsidiaries, at equity	626,890		591,969
Current assets
Cash and cash equivalents	42,205		2,239
Restricted cash	15,966		30,749
Advances to affiliates	26,700		27,700
Customer accounts receivable, net	102,736		105,454
Accrued unbilled revenues, net	73,628		83,148
Other accounts receivable, net	17,984		18,396
Fuel oil stock, at average cost	38,777		69,003
Materials and supplies, at average cost	38,786		34,876
Prepayments and other	34,306		88,334
Regulatory assets	22,095		27,689
Total current assets	413,183		487,588
Other long-term assets
Operating lease right-of-use-assets	125,858		174,886
Regulatory assets	513,192		476,390
Other	98,307		69,010
Total other long-term assets	737,357		720,286
Total assets	5,251,977		5,187,009
Capitalization
Common stock equity	2,141,918		2,047,352	1,957,641	1,845,283
Cumulative preferred stock–not subject to mandatory redemption	22,293		22,293
Long-term debt, net	1,116,426		1,006,737
Total capitalization	3,280,637		3,076,382
Current liabilities
Current portion of operating lease liabilities	64,599		63,582
Current portion of long-term debt, net			61,958
Short-term borrowings from non-affiliate	49,979		88,987
Short-term borrowings-affiliate	0		8,000
Accounts payable	97,102		139,056
Interest and dividends payable	14,480		14,759
Taxes accrued, including revenue taxes	135,018		143,522
Regulatory liabilities	20,224		13,363
Other	57,926		51,295
Total current liabilities	439,328		584,522
Deferred credits and other liabilities
Operating lease liabilities	67,824		111,598
Deferred income taxes	282,685		265,864
Regulatory liabilities	656,270		664,894
Unamortized tax credits	82,563		86,852
Defined benefit pension and other postretirement benefit plans liability	373,112		339,471
Other	69,558		57,426
Total deferred credits and other liabilities	1,532,012		1,526,105
Total capitalization and liabilities	5,251,977		5,187,009
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | HELCO
Utility property, plant and equipment
Land	5,606		5,606
Plant and equipment	1,352,885		1,313,727
Less accumulated depreciation	(597,606)		(574,615)
Construction in progress	13,043		9,993
Utility property, plant and equipment, net	773,928		754,711
Nonutility property, plant and equipment, less accumulated depreciation	115		114
Total property, plant and equipment, net	774,043		754,825
Investment in wholly-owned subsidiaries, at equity	0		0
Current assets
Cash and cash equivalents	3,046		6,885
Restricted cash	0		123
Advances to affiliates	0		8,000
Customer accounts receivable, net	23,989		24,520
Accrued unbilled revenues, net	13,631		17,071
Other accounts receivable, net	3,028		1,907
Fuel oil stock, at average cost	8,471		8,901
Materials and supplies, at average cost	9,896		8,313
Prepayments and other	5,197		3,725
Regulatory assets	1,954		1,641
Total current assets	69,212		81,086
Other long-term assets
Operating lease right-of-use-assets	1,443		1,537
Regulatory assets	114,461		109,163
Other	17,992		15,493
Total other long-term assets	133,896		126,193
Total assets	977,151		962,104
Capitalization
Common stock equity	317,451		298,998	295,874	286,647
Cumulative preferred stock–not subject to mandatory redemption	7,000		7,000
Long-term debt, net	216,447		206,416
Total capitalization	540,898		512,414
Current liabilities
Current portion of operating lease liabilities	98		94
Current portion of long-term debt, net			13,995
Short-term borrowings from non-affiliate	0		0
Short-term borrowings-affiliate	18,800		0
Accounts payable	19,570		25,629
Interest and dividends payable	3,138		3,115
Taxes accrued, including revenue taxes	29,869		32,541
Regulatory liabilities	8,785		9,454
Other	13,851		11,362
Total current liabilities	94,111		96,190
Deferred credits and other liabilities
Operating lease liabilities	1,344		1,442
Deferred income taxes	54,108		53,534
Regulatory liabilities	173,938		178,474
Unamortized tax credits	15,363		16,196
Defined benefit pension and other postretirement benefit plans liability	77,679		69,928
Other	19,710		33,926
Total deferred credits and other liabilities	342,142		353,500
Total capitalization and liabilities	977,151		962,104
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Maui Electric
Utility property, plant and equipment
Land	3,594		3,612
Plant and equipment	1,195,988		1,161,199
Less accumulated depreciation	(544,217)		(524,301)
Construction in progress	31,683		17,944
Utility property, plant and equipment, net	687,048		658,454
Nonutility property, plant and equipment, less accumulated depreciation	1,532		1,532
Total property, plant and equipment, net	688,580		659,986
Investment in wholly-owned subsidiaries, at equity	0		0
Current assets
Cash and cash equivalents	2,032		1,797
Restricted cash	0		0
Advances to affiliates	0		0
Customer accounts receivable, net	21,107		22,816
Accrued unbilled revenues, net	13,777		17,008
Other accounts receivable, net	2,856		1,960
Fuel oil stock, at average cost	10,990		14,033
Materials and supplies, at average cost	18,662		17,513
Prepayments and other	4,580		24,921
Regulatory assets	6,386		1,380
Total current assets	80,390		101,428
Other long-term assets
Operating lease right-of-use-assets	353		386
Regulatory assets	108,620		98,817
Other	20,010		17,215
Total other long-term assets	128,983		116,418
Total assets	897,953		877,832
Capitalization
Common stock equity	309,363		292,870	280,863	270,265
Cumulative preferred stock–not subject to mandatory redemption	5,000		5,000
Long-term debt, net	228,429		188,561
Total capitalization	542,792		486,431
Current liabilities
Current portion of operating lease liabilities	33		31
Current portion of long-term debt, net			20,000
Short-term borrowings from non-affiliate	0		0
Short-term borrowings-affiliate	7,900		27,700
Accounts payable	17,177		23,085
Interest and dividends payable	2,790		2,900
Taxes accrued, including revenue taxes	27,637		31,929
Regulatory liabilities	8,292		7,907
Other	18,621		15,297
Total current liabilities	82,450		128,849
Deferred credits and other liabilities
Operating lease liabilities	326		360
Deferred income taxes	61,005		57,752
Regulatory liabilities	92,277		98,218
Unamortized tax credits	13,989		14,820
Defined benefit pension and other postretirement benefit plans liability	79,741		69,364
Other	25,373		22,038
Total deferred credits and other liabilities	272,711		262,552
Total capitalization and liabilities	897,953		877,832
Hawaiian Electric Company, Inc. and Subsidiaries | 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		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
Common stock 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, net			0
Short-term borrowings from non-affiliate	0		0
Short-term borrowings-affiliate	0		0
Accounts payable	0		0
Interest and 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 capitalization and liabilities	77		101
Hawaiian Electric Company, Inc. and Subsidiaries | 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	(626,890)		(591,969)
Current assets
Cash and cash equivalents	0		0
Restricted cash	0		0
Advances to affiliates	(26,700)		(35,700)
Customer accounts receivable, net	0		0
Accrued unbilled revenues, net	0		0
Other accounts receivable, net	(16,195)		(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	(42,895)		(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	(669,785)		(638,364)
Capitalization
Common stock equity	(626,891)		(591,969)	$ (576,838)	$ (557,013)
Cumulative preferred stock–not subject to mandatory redemption	0		0
Long-term debt, net	0		0
Total capitalization	(626,891)		(591,969)
Current liabilities
Current portion of operating lease liabilities	0		0
Current portion of long-term debt, net			0
Short-term borrowings from non-affiliate	0		0
Short-term borrowings-affiliate	(26,700)		(35,700)
Accounts payable	0		0
Interest and dividends payable	(58)		(46)
Taxes accrued, including revenue taxes	0		0
Regulatory liabilities	0		0
Other	(16,136)		(10,649)
Total current liabilities	(42,894)		(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 capitalization and liabilities	$ (669,785)		$ (638,364)