Electric utility segment - Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Utility property, plant and equipment
Total property, plant and equipment, net	$ 5,109,628	$ 4,830,118
Current assets
Cash and cash equivalents	196,813	169,208	$ 261,881
Restricted cash	30,872	0
Other long-term assets
Operating lease right-of-use-assets	199,171
Total assets	13,745,251	13,104,051	12,534,160
Capitalization
Common stock equity	2,280,260	2,162,280	2,097,386	$ 2,066,753
Cumulative preferred stock – not subject to mandatory redemption	0	0
Current portion of operating lease liabilities	63,707
Current liabilities
Interest and dividends payable	24,941	28,254
Deferred credits and other liabilities
Deferred income taxes	379,324	372,518
Total capitalization and liabilities	13,745,251	13,104,051
Parent Company
Utility property, plant and equipment
Total property, plant and equipment, net	2,931	3,456
Other long-term assets
Total assets	2,821,587	2,657,739
Capitalization
Common stock equity	2,280,260	2,162,280
Cumulative preferred stock – not subject to mandatory redemption	0	0
Deferred credits and other liabilities
Total capitalization and liabilities	2,821,587	2,657,739
Hawaiian Electric Company, Inc. and Subsidiaries
Utility property, plant and equipment
Land	51,816	49,667
Plant and equipment	7,240,288	6,809,671
Less accumulated depreciation	(2,690,157)	(2,577,342)
Construction in progress	193,074	233,145
Utility property, plant and equipment, net	4,795,021	4,515,141
Nonutility property, plant and equipment, less accumulated depreciation	6,956	6,961
Total property, plant and equipment, net	4,801,977	4,522,102
Investment in wholly-owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	11,022	35,877	12,517
Restricted cash	30,872
Advances to affiliates	0
Customer accounts receivable, net	152,790	177,896
Accrued unbilled revenues, net	117,227	121,738
Other accounts receivable, net	11,568	6,215
Fuel oil stock, at average cost	91,937	79,935
Materials and supplies, at average cost	60,702	55,204
Prepayments and other	116,980	32,118
Regulatory assets	30,710	71,016
Total current assets	623,808	579,999
Other long-term assets
Operating lease right-of-use-assets	176,809
Regulatory assets	684,370	762,410
Other	101,718	102,992
Total other long-term assets	962,897	865,402
Total assets	6,388,682	5,967,503
Capitalization
Common stock equity	2,047,352	1,957,641	1,845,283	1,799,787
Cumulative preferred stock – not subject to mandatory redemption	34,293	34,293
Long-term debt, net	1,401,714	1,418,802
Total capitalization	3,483,359	3,410,736
Current portion of operating lease liabilities	63,707
Current liabilities
Current portion of long-term debt, net	95,953	0
Short-term borrowings from non-affiliate	88,987	25,000
Short-term borrowings-affiliate	0
Accounts payable	187,770	171,791
Interest and dividends payable	20,728	23,215
Taxes accrued, including revenue taxes	207,992	233,333
Regulatory liabilities	30,724	17,977
Other	67,305	60,003
Total current liabilities	763,166	531,319
Operating lease liabilities	113,400
Deferred credits and other liabilities
Deferred income taxes	377,150	383,197
Regulatory liabilities	941,586	932,259
Unamortized tax credits	117,868	91,522
Defined benefit pension and other postretirement benefit plans liability	478,763	503,659
Other	113,390	114,811
Total deferred credits and other liabilities	2,142,157	2,025,448
Total capitalization and liabilities	6,388,682	5,967,503
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Parent Company
Utility property, plant and equipment
Land	42,598	40,449
Plant and equipment	4,765,362	4,456,090
Less accumulated depreciation	(1,591,241)	(1,523,861)
Construction in progress	165,137	193,677
Utility property, plant and equipment, net	3,381,856	3,166,355
Nonutility property, plant and equipment, less accumulated depreciation	5,310	5,314
Total property, plant and equipment, net	3,387,166	3,171,669
Investment in wholly-owned subsidiaries, at equity	591,969	576,838
Current assets
Cash and cash equivalents	2,239	16,732
Restricted cash	30,749
Advances to affiliates	27,700
Customer accounts receivable, net	105,454	125,960
Accrued unbilled revenues, net	83,148	88,060
Other accounts receivable, net	18,396	21,962
Fuel oil stock, at average cost	69,003	54,262
Materials and supplies, at average cost	34,876	30,291
Prepayments and other	88,334	23,214
Regulatory assets	27,689	60,093
Total current assets	487,588	420,574
Other long-term assets
Operating lease right-of-use-assets	174,886
Regulatory assets	476,390	537,708
Other	69,010	69,749
Total other long-term assets	720,286	607,457
Total assets	5,187,009	4,776,538
Capitalization
Common stock equity	2,047,352	1,957,641	1,845,283	1,799,787
Cumulative preferred stock – not subject to mandatory redemption	22,293	22,293
Long-term debt, net	1,006,737	1,000,137
Total capitalization	3,076,382	2,980,071
Current portion of operating lease liabilities	63,582
Current liabilities
Current portion of long-term debt, net	61,958
Short-term borrowings from non-affiliate	88,987	25,000
Short-term borrowings-affiliate	8,000
Accounts payable	139,056	126,384
Interest and dividends payable	14,759	16,203
Taxes accrued, including revenue taxes	143,522	164,747
Regulatory liabilities	13,363	7,699
Other	51,295	46,391
Total current liabilities	584,522	386,424
Operating lease liabilities	111,598
Deferred credits and other liabilities
Deferred income taxes	265,864	271,438
Regulatory liabilities	664,894	657,210
Unamortized tax credits	86,852	60,271
Defined benefit pension and other postretirement benefit plans liability	339,471	359,174
Other	57,426	61,950
Total deferred credits and other liabilities	1,526,105	1,410,043
Total capitalization and liabilities	5,187,009	4,776,538
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Hawaii Electric Light
Utility property, plant and equipment
Land	5,606	5,606
Plant and equipment	1,313,727	1,259,553
Less accumulated depreciation	(574,615)	(547,848)
Construction in progress	9,993	8,781
Utility property, plant and equipment, net	754,711	726,092
Nonutility property, plant and equipment, less accumulated depreciation	114	115
Total property, plant and equipment, net	754,825	726,207
Investment in wholly-owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	6,885	15,623
Restricted cash	123
Advances to affiliates	8,000
Customer accounts receivable, net	24,520	26,483
Accrued unbilled revenues, net	17,071	17,051
Other accounts receivable, net	1,907	3,131
Fuel oil stock, at average cost	8,901	11,027
Materials and supplies, at average cost	8,313	7,155
Prepayments and other	3,725	5,212
Regulatory assets	1,641	3,177
Total current assets	81,086	88,859
Other long-term assets
Operating lease right-of-use-assets	1,537
Regulatory assets	109,163	120,658
Other	15,493	15,944
Total other long-term assets	126,193	136,602
Total assets	962,104	951,668
Capitalization
Common stock equity	298,998	295,874	286,647	291,291
Cumulative preferred stock – not subject to mandatory redemption	7,000	7,000
Long-term debt, net	206,416	217,749
Total capitalization	512,414	520,623
Current portion of operating lease liabilities	94
Current liabilities
Current portion of long-term debt, net	13,995
Short-term borrowings from non-affiliate	0	0
Short-term borrowings-affiliate	0
Accounts payable	25,629	20,045
Interest and dividends payable	3,115	4,203
Taxes accrued, including revenue taxes	32,541	34,128
Regulatory liabilities	9,454	4,872
Other	11,362	15,077
Total current liabilities	96,190	78,325
Operating lease liabilities	1,442
Deferred credits and other liabilities
Deferred income taxes	53,534	54,936
Regulatory liabilities	178,474	176,101
Unamortized tax credits	16,196	16,217
Defined benefit pension and other postretirement benefit plans liability	69,928	73,147
Other	33,926	32,319
Total deferred credits and other liabilities	353,500	352,720
Total capitalization and liabilities	962,104	951,668
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Maui Electric
Utility property, plant and equipment
Land	3,612	3,612
Plant and equipment	1,161,199	1,094,028
Less accumulated depreciation	(524,301)	(505,633)
Construction in progress	17,944	30,687
Utility property, plant and equipment, net	658,454	622,694
Nonutility property, plant and equipment, less accumulated depreciation	1,532	1,532
Total property, plant and equipment, net	659,986	624,226
Investment in wholly-owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	1,797	3,421
Restricted cash	0
Advances to affiliates	0
Customer accounts receivable, net	22,816	25,453
Accrued unbilled revenues, net	17,008	16,627
Other accounts receivable, net	1,960	3,033
Fuel oil stock, at average cost	14,033	14,646
Materials and supplies, at average cost	17,513	17,758
Prepayments and other	24,921	3,692
Regulatory assets	1,380	7,746
Total current assets	101,428	92,376
Other long-term assets
Operating lease right-of-use-assets	386
Regulatory assets	98,817	104,044
Other	17,215	17,299
Total other long-term assets	116,418	121,343
Total assets	877,832	837,945
Capitalization
Common stock equity	292,870	280,863	270,265	259,554
Cumulative preferred stock – not subject to mandatory redemption	5,000	5,000
Long-term debt, net	188,561	200,916
Total capitalization	486,431	486,779
Current portion of operating lease liabilities	31
Current liabilities
Current portion of long-term debt, net	20,000
Short-term borrowings from non-affiliate	0	0
Short-term borrowings-affiliate	27,700
Accounts payable	23,085	25,362
Interest and dividends payable	2,900	2,841
Taxes accrued, including revenue taxes	31,929	34,458
Regulatory liabilities	7,907	5,406
Other	15,297	20,414
Total current liabilities	128,849	88,481
Operating lease liabilities	360
Deferred credits and other liabilities
Deferred income taxes	57,752	56,823
Regulatory liabilities	98,218	98,948
Unamortized tax credits	14,820	15,034
Defined benefit pension and other postretirement benefit plans liability	69,364	71,338
Other	22,038	20,542
Total deferred credits and other liabilities	262,552	262,685
Total capitalization and liabilities	877,832	837,945
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	101	101
Restricted cash	0
Advances to affiliates	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
Regulatory assets	0	0
Other	0	0
Total other long-term assets	0	0
Total assets	101	101
Capitalization
Common stock 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 portion of operating lease liabilities	0
Current liabilities
Current portion of long-term debt, net	0
Short-term borrowings from non-affiliate	0	0
Short-term borrowings-affiliate	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
Operating lease liabilities	0
Deferred credits and other liabilities
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	101	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	(591,969)	(576,838)
Current assets
Cash and cash equivalents	0	0
Restricted cash	0
Advances to affiliates	(35,700)
Customer accounts receivable, net	0	0
Accrued unbilled revenues, net	0	0
Other accounts receivable, net	(10,695)	(21,911)
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	(46,395)	(21,911)
Other long-term assets
Operating lease right-of-use-assets	0
Regulatory assets	0	0
Other	0	0
Total other long-term assets	0	0
Total assets	(638,364)	(598,749)
Capitalization
Common stock equity	(591,969)	(576,838)	$ (557,013)	$ (550,946)
Cumulative preferred stock – not subject to mandatory redemption	0	0
Long-term debt, net	0	0
Total capitalization	(591,969)	(576,838)
Current portion of operating lease liabilities	0
Current liabilities
Current portion of long-term debt, net	0
Short-term borrowings from non-affiliate	0	0
Short-term borrowings-affiliate	(35,700)
Accounts payable	0	0
Interest and dividends payable	(46)	(32)
Taxes accrued, including revenue taxes	0	0
Regulatory liabilities	0	0
Other	(10,649)	(21,879)
Total current liabilities	(46,395)	(21,911)
Operating lease liabilities	0
Deferred credits and other liabilities
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	$ (638,364)	$ (598,749)