Electric utility segment - Condensed consolidating balance sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Utility property, plant and equipment
Total property, plant and equipment, net	$ 4,694,101	$ 4,460,248
Current assets
Cash and cash equivalents	172,054	261,881	$ 202,173	$ 278,452
Other long-term assets
Total assets	12,911,554	12,534,160
Capitalization
Common stock equity	2,132,045	2,097,386	2,103,022	2,066,753
Cumulative preferred stock—not subject to mandatory redemption	0	0
Current liabilities
Interest and preferred dividends payable	30,280	25,837
Deferred credits and other liabilities
Deferred income taxes	385,651	388,430
Total liabilities and shareholders’ equity	12,911,554	12,534,160
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	(571,574)	(557,013)
Current assets
Cash and cash equivalents	0	0	0	0
Advances to affiliates	(2,000)	(12,000)
Customer accounts receivable, net	0	0
Accrued unbilled revenues, net	0	0
Other accounts receivable, net	(9,355)	(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	(11,355)	(19,691)
Other long-term assets
Regulatory assets	0	0
Other	0	0
Total other long-term assets	0	0
Total assets	(582,929)	(576,704)
Capitalization
Common stock equity	(571,574)	(557,013)	(559,671)	(550,946)
Cumulative preferred stock—not subject to mandatory redemption	0	0
Long-term debt, net	0	0
Total capitalization	(571,574)	(557,013)
Current liabilities
Current portion of long-term debt	0	0
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	(2,000)	(12,000)
Accounts payable	0	0
Interest and preferred dividends payable	(9)	(11)
Taxes accrued	0	0
Regulatory liabilities	0	0
Other	(9,346)	(7,680)
Total current liabilities	(11,355)	(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 liabilities and shareholders’ equity	(582,929)	(576,704)
Hawaiian Electric (parent only) | Reportable Legal Entities
Utility property, plant and equipment
Land	44,030	43,972
Plant and equipment	4,404,946	4,140,892
Less accumulated depreciation	(1,513,351)	(1,451,612)
Construction in progress	154,566	231,571
Utility property, plant and equipment, net	3,090,191	2,964,823
Nonutility property, plant and equipment, less accumulated depreciation	5,933	5,933
Total property, plant and equipment, net	3,096,124	2,970,756
Investment in wholly owned subsidiaries, at equity	571,574	557,013
Current assets
Cash and cash equivalents	3,867	2,059	3,454	61,388
Advances to affiliates	2,000	0
Customer accounts receivable, net	124,792	86,987
Accrued unbilled revenues, net	94,956	77,176
Other accounts receivable, net	10,312	11,376
Fuel oil stock, at average cost	61,110	64,972
Materials and supplies, at average cost	32,407	28,325
Prepayments and other	44,458	17,928
Regulatory assets	75,541	76,203
Total current assets	449,443	365,026
Other long-term assets
Regulatory assets	527,650	557,464
Other	77,899	60,157
Total other long-term assets	605,549	617,621
Total assets	4,722,690	4,510,416
Capitalization
Common stock equity	1,876,237	1,845,283	1,829,075	1,799,787
Cumulative preferred stock—not subject to mandatory redemption	22,293	22,293
Long-term debt, net	1,000,020	924,979
Total capitalization	2,898,550	2,792,555
Current liabilities
Current portion of long-term debt	29,996	29,978
Short-term borrowings from non-affiliates	85,913	4,999
Short-term borrowings from affiliate	0	12,000
Accounts payable	90,937	121,328
Interest and preferred dividends payable	19,994	15,677
Taxes accrued	136,485	133,839
Regulatory liabilities	3,124	607
Other	64,697	43,121
Total current liabilities	431,146	361,549
Deferred credits and other liabilities
Deferred income taxes	285,789	281,223
Regulatory liabilities	649,761	613,329
Unamortized tax credits	61,299	59,039
Defined benefit pension and other postretirement benefit plans liability	332,743	340,983
Other	63,402	61,738
Total deferred credits and other liabilities	1,392,994	1,356,312
Total liabilities and shareholders’ equity	4,722,690	4,510,416
HELCO | Reportable Legal Entities
Utility property, plant and equipment
Land	5,873	6,189
Plant and equipment	1,227,530	1,206,776
Less accumulated depreciation	(541,451)	(528,024)
Construction in progress	11,060	8,182
Utility property, plant and equipment, net	703,012	693,123
Nonutility property, plant and equipment, less accumulated depreciation	115	115
Total property, plant and equipment, net	703,127	693,238
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	3,027	4,025	4,714	10,749
Advances to affiliates	0	0
Customer accounts receivable, net	29,364	22,510
Accrued unbilled revenues, net	15,810	15,940
Other accounts receivable, net	1,352	2,268
Fuel oil stock, at average cost	11,483	8,698
Materials and supplies, at average cost	7,840	8,041
Prepayments and other	8,604	4,514
Regulatory assets	6,217	5,038
Total current assets	83,697	71,034
Other long-term assets
Regulatory assets	115,114	122,783
Other	20,363	16,311
Total other long-term assets	135,477	139,094
Total assets	922,301	903,366
Capitalization
Common stock equity	294,220	286,647	294,319	291,291
Cumulative preferred stock—not subject to mandatory redemption	7,000	7,000
Long-term debt, net	217,724	202,701
Total capitalization	518,944	496,348
Current liabilities
Current portion of long-term debt	10,998	10,992
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	0	0
Accounts payable	12,289	17,855
Interest and preferred dividends payable	4,243	4,174
Taxes accrued	30,829	34,950
Regulatory liabilities	2,850	1,245
Other	9,594	9,818
Total current liabilities	70,803	79,034
Deferred credits and other liabilities
Deferred income taxes	56,417	56,955
Regulatory liabilities	174,739	169,139
Unamortized tax credits	16,271	16,167
Defined benefit pension and other postretirement benefit plans liability	64,026	66,447
Other	21,101	19,276
Total deferred credits and other liabilities	332,554	327,984
Total liabilities and shareholders’ equity	922,301	903,366
Maui Electric | Reportable Legal Entities
Utility property, plant and equipment
Land	3,612	3,016
Plant and equipment	1,087,570	1,053,372
Less accumulated depreciation	(512,906)	(496,716)
Construction in progress	27,460	23,341
Utility property, plant and equipment, net	605,736	583,013
Nonutility property, plant and equipment, less accumulated depreciation	1,532	1,532
Total property, plant and equipment, net	607,268	584,545
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	229	6,332	1,718	2,048
Advances to affiliates	0	12,000
Customer accounts receivable, net	24,629	18,392
Accrued unbilled revenues, net	16,936	13,938
Other accounts receivable, net	1,069	1,210
Fuel oil stock, at average cost	19,229	13,203
Materials and supplies, at average cost	18,260	18,031
Prepayments and other	7,670	2,913
Regulatory assets	7,672	7,149
Total current assets	95,694	93,168
Other long-term assets
Regulatory assets	98,730	100,660
Other	18,272	15,061
Total other long-term assets	117,002	115,721
Total assets	819,964	793,434
Capitalization
Common stock equity	277,253	270,265	265,251	259,554
Cumulative preferred stock—not subject to mandatory redemption	5,000	5,000
Long-term debt, net	200,887	190,836
Total capitalization	483,140	466,101
Current liabilities
Current portion of long-term debt	8,999	8,993
Short-term borrowings from non-affiliates	0	0
Short-term borrowings from affiliate	2,000	0
Accounts payable	19,706	20,427
Interest and preferred dividends payable	4,030	2,735
Taxes accrued	28,462	30,312
Regulatory liabilities	4,185	1,549
Other	16,109	14,197
Total current liabilities	83,491	78,213
Deferred credits and other liabilities
Deferred income taxes	58,863	55,863
Regulatory liabilities	97,693	94,901
Unamortized tax credits	15,503	15,163
Defined benefit pension and other postretirement benefit plans liability	63,510	65,518
Other	17,764	17,675
Total deferred credits and other liabilities	253,333	249,120
Total liabilities and shareholders’ equity	819,964	793,434
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	101	101	101	101
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
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	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
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	53,515	53,177
Plant and equipment	6,720,046	6,401,040
Less accumulated depreciation	(2,567,708)	(2,476,352)
Construction in progress	193,086	263,094
Utility property, plant and equipment, net	4,398,939	4,240,959
Nonutility property, plant and equipment, less accumulated depreciation	7,580	7,580
Total property, plant and equipment, net	4,406,519	4,248,539
Investment in wholly owned subsidiaries, at equity	0	0
Current assets
Cash and cash equivalents	7,224	12,517	9,987	74,286
Advances to affiliates	0	0
Customer accounts receivable, net	178,785	127,889
Accrued unbilled revenues, net	127,702	107,054
Other accounts receivable, net	3,378	7,163
Fuel oil stock, at average cost	91,822	86,873
Materials and supplies, at average cost	58,507	54,397
Prepayments and other	60,732	25,355
Regulatory assets	89,430	88,390
Total current assets	617,580	509,638
Other long-term assets
Regulatory assets	741,494	780,907
Other	116,534	91,529
Total other long-term assets	858,028	872,436
Total assets	5,882,127	5,630,613
Capitalization
Common stock equity	1,876,237	1,845,283	$ 1,829,075	$ 1,799,787
Cumulative preferred stock—not subject to mandatory redemption	34,293	34,293
Long-term debt, net	1,418,631	1,318,516
Total capitalization	3,329,161	3,198,092
Current liabilities
Current portion of long-term debt	49,993	49,963
Short-term borrowings from non-affiliates	85,913	4,999
Short-term borrowings from affiliate	0	0
Accounts payable	122,932	159,610
Interest and preferred dividends payable	28,258	22,575
Taxes accrued	195,776	199,101
Regulatory liabilities	10,159	3,401
Other	81,054	59,456
Total current liabilities	574,085	499,105
Deferred credits and other liabilities
Deferred income taxes	401,069	394,041
Regulatory liabilities	922,193	877,369
Unamortized tax credits	93,073	90,369
Defined benefit pension and other postretirement benefit plans liability	460,279	472,948
Other	102,267	98,689
Total deferred credits and other liabilities	1,978,881	1,933,416
Total liabilities and shareholders’ equity	$ 5,882,127	$ 5,630,613