Electric utility segment - Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Utility property, plant and equipment
Total property, plant and equipment, net	$ 4,830,118	$ 4,460,248
Other long-term assets
Total assets	13,104,051	12,534,160	$ 11,881,981
Capitalization
Common stock equity	2,162,280	2,097,386	2,066,753	$ 1,927,640
Cumulative preferred stock – not subject to mandatory redemption	0	0
Current liabilities
Interest and dividends payable	28,254	25,837
Deferred credits and other liabilities
Deferred income taxes	372,518	388,430
Total capitalization and liabilities	13,104,051	12,534,160
Hawaiian Electric
Utility property, plant and equipment
Land	40,449	40,392
Plant and equipment	4,456,090	4,144,472
Less accumulated depreciation	(1,523,861)	(1,451,612)
Construction in progress	193,677	231,571
Utility property, plant and equipment, net	3,166,355	2,964,823
Nonutility property, plant and equipment, less accumulated depreciation	5,314	5,933
Total property, plant and equipment, net	3,171,669	2,970,756
Investment in wholly-owned subsidiaries, at equity	576,838	557,013
Current assets
Cash and cash equivalents	16,732	2,059	61,388	16,281
Advances to affiliates		0
Customer accounts receivable, net	125,960	86,987
Accrued unbilled revenues, net	88,060	77,176
Other accounts receivable, net	21,962	11,376
Fuel oil stock, at average cost	54,262	64,972
Materials and supplies, at average cost	30,291	28,325
Prepayments and other	23,214	17,928
Regulatory assets	60,093	76,203
Total current assets	420,574	365,026
Other long-term assets
Regulatory assets	537,708	557,464
Other	69,749	60,157
Total other long-term assets	607,457	617,621
Total assets	4,776,538	4,510,416
Capitalization
Common stock equity	1,957,641	1,845,283	1,799,787	1,728,325
Cumulative preferred stock – not subject to mandatory redemption	22,293	22,293
Long-term debt, net	1,000,137	924,979
Total capitalization	2,980,071	2,792,555
Current liabilities
Current portion of long-term debt		29,978
Short-term borrowings from non-affiliate	25,000	4,999
Short-term borrowings-affiliate		12,000
Accounts payable	126,384	121,328
Interest and dividends payable	16,203	15,677
Taxes accrued, including revenue taxes	164,747	133,839
Regulatory liabilities	7,699	607
Other	46,391	43,121
Total current liabilities	386,424	361,549
Deferred credits and other liabilities
Deferred income taxes	271,438	281,223
Regulatory liabilities	657,210	613,329
Unamortized tax credits	60,271	59,039
Defined benefit pension and other postretirement benefit plans liability	359,174	340,983
Other	61,950	61,738
Total deferred credits and other liabilities	1,410,043	1,356,312
Total capitalization and liabilities	4,776,538	4,510,416
Hawaii Electric Light Company, Inc. (HELCO)
Utility property, plant and equipment
Land	5,606	5,922
Plant and equipment	1,259,553	1,207,043
Less accumulated depreciation	(547,848)	(528,024)
Construction in progress	8,781	8,182
Utility property, plant and equipment, net	726,092	693,123
Nonutility property, plant and equipment, less accumulated depreciation	115	115
Total property, plant and equipment, net	726,207	693,238
Investment in wholly-owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	15,623	4,025	10,749	2,682
Advances to affiliates		0
Customer accounts receivable, net	26,483	22,510
Accrued unbilled revenues, net	17,051	15,940
Other accounts receivable, net	3,131	2,268
Fuel oil stock, at average cost	11,027	8,698
Materials and supplies, at average cost	7,155	8,041
Prepayments and other	5,212	4,514
Regulatory assets	3,177	5,038
Total current assets	88,859	71,034
Other long-term assets
Regulatory assets	120,658	122,783
Other	15,944	16,311
Total other long-term assets	136,602	139,094
Total assets	951,668	903,366
Capitalization
Common stock equity	295,874	286,647	291,291	292,702
Cumulative preferred stock – not subject to mandatory redemption	7,000	7,000
Long-term debt, net	217,749	202,701
Total capitalization	520,623	496,348
Current liabilities
Current portion of long-term debt		10,992
Short-term borrowings from non-affiliate	0	0
Short-term borrowings-affiliate		0
Accounts payable	20,045	17,855
Interest and dividends payable	4,203	4,174
Taxes accrued, including revenue taxes	34,128	34,950
Regulatory liabilities	4,872	1,245
Other	15,077	9,818
Total current liabilities	78,325	79,034
Deferred credits and other liabilities
Deferred income taxes	54,936	56,955
Regulatory liabilities	176,101	169,139
Unamortized tax credits	16,217	16,167
Defined benefit pension and other postretirement benefit plans liability	73,147	66,447
Other	32,319	19,276
Total deferred credits and other liabilities	352,720	327,984
Total capitalization and liabilities	951,668	903,366
Maui Electric Company, Limited (MECO)
Utility property, plant and equipment
Land	3,612	3,016
Plant and equipment	1,094,028	1,053,372
Less accumulated depreciation	(505,633)	(496,716)
Construction in progress	30,687	23,341
Utility property, plant and equipment, net	622,694	583,013
Nonutility property, plant and equipment, less accumulated depreciation	1,532	1,532
Total property, plant and equipment, net	624,226	584,545
Investment in wholly-owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	3,421	6,332	2,048	5,385
Advances to affiliates		12,000
Customer accounts receivable, net	25,453	18,392
Accrued unbilled revenues, net	16,627	13,938
Other accounts receivable, net	3,033	1,210
Fuel oil stock, at average cost	14,646	13,203
Materials and supplies, at average cost	17,758	18,031
Prepayments and other	3,692	2,913
Regulatory assets	7,746	7,149
Total current assets	92,376	93,168
Other long-term assets
Regulatory assets	104,044	100,660
Other	17,299	15,061
Total other long-term assets	121,343	115,721
Total assets	837,945	793,434
Capitalization
Common stock equity	280,863	270,265	259,554	263,725
Cumulative preferred stock – not subject to mandatory redemption	5,000	5,000
Long-term debt, net	200,916	190,836
Total capitalization	486,779	466,101
Current liabilities
Current portion of long-term debt		8,993
Short-term borrowings from non-affiliate	0	0
Short-term borrowings-affiliate		0
Accounts payable	25,362	20,427
Interest and dividends payable	2,841	2,735
Taxes accrued, including revenue taxes	34,458	30,312
Regulatory liabilities	5,406	1,549
Other	20,414	14,197
Total current liabilities	88,481	78,213
Deferred credits and other liabilities
Deferred income taxes	56,823	55,863
Regulatory liabilities	98,948	94,901
Unamortized tax credits	15,034	15,163
Defined benefit pension and other postretirement benefit plans liability	71,338	65,518
Other	20,542	17,675
Total deferred credits and other liabilities	262,685	249,120
Total capitalization and liabilities	837,945	793,434
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	101	101
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
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 liabilities
Current portion of long-term debt		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
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
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	(576,838)	(557,013)
Current assets
Cash and cash equivalents	0	0	0	0
Advances to affiliates		(12,000)
Customer accounts receivable, net	0	0
Accrued unbilled revenues, net	0	0
Other accounts receivable, net	(21,911)	(7,691)
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	(21,911)	(19,691)
Other long-term assets
Regulatory assets	0	0
Other	0	0
Total other long-term assets	0	0
Total assets	(598,749)	(576,704)
Capitalization
Common stock equity	(576,838)	(557,013)	(550,946)	(556,528)
Cumulative preferred stock – not subject to mandatory redemption	0	0
Long-term debt, net	0	0
Total capitalization	(576,838)	(557,013)
Current liabilities
Current portion of long-term debt		0
Short-term borrowings from non-affiliate	0	0
Short-term borrowings-affiliate		(12,000)
Accounts payable	0	0
Interest and dividends payable	(32)	(11)
Taxes accrued, including revenue taxes	0	0
Regulatory liabilities	0	0
Other	(21,879)	(7,680)
Total current liabilities	(21,911)	(19,691)
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	(598,749)	(576,704)
HECO Consolidated
Utility property, plant and equipment
Land	49,667	49,330
Plant and equipment	6,809,671	6,404,887
Less accumulated depreciation	(2,577,342)	(2,476,352)
Construction in progress	233,145	263,094
Utility property, plant and equipment, net	4,515,141	4,240,959
Nonutility property, plant and equipment, less accumulated depreciation	6,961	7,580
Total property, plant and equipment, net	4,522,102	4,248,539
Investment in wholly-owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	35,877	12,517	74,286	24,449
Advances to affiliates		0
Customer accounts receivable, net	177,896	127,889
Accrued unbilled revenues, net	121,738	107,054
Other accounts receivable, net	6,215	7,163
Fuel oil stock, at average cost	79,935	86,873
Materials and supplies, at average cost	55,204	54,397
Prepayments and other	32,118	25,355
Regulatory assets	71,016	88,390
Total current assets	579,999	509,638
Other long-term assets
Regulatory assets	762,410	780,907
Other	102,992	91,529
Total other long-term assets	865,402	872,436
Total assets	5,967,503	5,630,613
Capitalization
Common stock equity	1,957,641	1,845,283	$ 1,799,787	$ 1,728,325
Cumulative preferred stock – not subject to mandatory redemption	34,293	34,293
Long-term debt, net	1,418,802	1,318,516
Total capitalization	3,410,736	3,198,092
Current liabilities
Current portion of long-term debt	0	49,963
Short-term borrowings from non-affiliate	25,000	4,999
Short-term borrowings-affiliate		0
Accounts payable	171,791	159,610
Interest and dividends payable	23,215	22,575
Taxes accrued, including revenue taxes	233,333	199,101
Regulatory liabilities	17,977	3,401
Other	60,003	59,456
Total current liabilities	531,319	499,105
Deferred credits and other liabilities
Deferred income taxes	383,197	394,041
Regulatory liabilities	932,259	877,369
Unamortized tax credits	91,522	90,369
Defined benefit pension and other postretirement benefit plans liability	503,659	472,948
Other	114,811	98,689
Total deferred credits and other liabilities	2,025,448	1,933,416
Total capitalization and liabilities	$ 5,967,503	$ 5,630,613