Electric utility segment - Consolidating Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Utility property, plant and equipment
Total property, plant and equipment, net	$ 4,603,465	$ 4,377,658
Other long-term assets
Total assets	12,425,506	11,782,018	$ 11,177,143
Capitalization
Common stock equity	2,066,753	1,927,640	1,790,573	$ 1,726,406
Cumulative preferred stock – not subject to mandatory redemption	0	0
Liabilities
Interest and dividends payable	25,225	26,042
Deferred credits and other liabilities
Deferred income taxes	728,806	680,877
Contributions in aid of construction	543,525	506,087
Total capitalization and liabilities	12,425,506	11,782,018
HECO
Utility property, plant and equipment
Land	43,956	43,557
Plant and equipment	4,241,060	4,026,079
Less accumulated depreciation	(1,382,972)	(1,316,467)
Construction in progress	180,194	147,979
Utility property, plant and equipment, net	3,082,238	2,901,148
Nonutility property, plant and equipment, less accumulated depreciation	5,760	5,659
Total property, plant and equipment, net	3,087,998	2,906,807
Investment in wholly-owned subsidiaries, at equity	550,946	556,528
Assets, Current [Abstract]
Cash and cash equivalents	61,388	16,281	12,416	61,245
Advances to affiliates	0	0
Customer accounts receivable, net	86,373	93,515
Accrued unbilled revenues, net	65,821	60,080
Other accounts receivable, net	7,652	16,421
Fuel oil stock, at average cost	47,239	49,455
Materials and supplies, at average cost	29,928	30,921
Prepayments and other	16,502	25,505
Regulatory assets	60,185	63,615
Total current assets	375,088	355,793
Other long-term assets
Regulatory assets	662,232	608,957
Unamortized debt expense	151	359
Other	43,743	47,731
Total other long-term assets	706,126	657,047
Total assets	4,720,158	4,476,175
Capitalization
Common stock equity	1,799,787	1,728,325	1,682,144	1,593,564
Cumulative preferred stock – not subject to mandatory redemption	22,293	22,293
Long-term debt, net	915,437	875,163
Total capitalization	2,737,517	2,625,781
Liabilities
Short-term borrowings-affiliate	13,500	23,000
Accounts payable	86,369	84,631
Interest and dividends payable	15,761	15,747
Taxes accrued	120,176	131,668
Regulatory liabilities	0	0
Other	41,352	41,083
Total current liabilities	277,158	296,129
Deferred credits and other liabilities
Deferred income taxes	524,433	466,133
Regulatory liabilities	281,112	254,033
Unamortized tax credits	57,844	54,078
Defined benefit pension and other postretirement benefit plans liability	444,458	409,021
Other	49,191	51,273
Total deferred credits and other liabilities	1,357,038	1,234,538
Contributions in aid of construction	348,445	319,727
Total capitalization and liabilities	4,720,158	4,476,175
Hawaii Electric Light Company, Inc. (HELCO)
Utility property, plant and equipment
Land	6,181	6,219
Plant and equipment	1,255,185	1,212,195
Less accumulated depreciation	(507,666)	(486,028)
Construction in progress	12,510	11,455
Utility property, plant and equipment, net	766,210	743,841
Nonutility property, plant and equipment, less accumulated depreciation	115	82
Total property, plant and equipment, net	766,325	743,923
Assets, Current [Abstract]
Cash and cash equivalents	10,749	2,682	612	1,326
Advances to affiliates	3,500	15,500
Customer accounts receivable, net	20,055	20,508
Accrued unbilled revenues, net	13,564	12,531
Other accounts receivable, net	2,445	1,275
Fuel oil stock, at average cost	8,229	8,310
Materials and supplies, at average cost	7,380	6,865
Prepayments and other	5,352	9,091
Regulatory assets	3,483	4,501
Total current assets	74,757	81,263
Other long-term assets
Regulatory assets	120,863	114,562
Unamortized debt expense	23	74
Other	13,573	14,693
Total other long-term assets	134,459	129,329
Total assets	975,541	954,515
Capitalization
Common stock equity	291,291	292,702	281,846	274,802
Cumulative preferred stock – not subject to mandatory redemption	7,000	7,000
Long-term debt, net	213,703	213,580
Total capitalization	511,994	513,282
Liabilities
Short-term borrowings-affiliate	0	0
Accounts payable	18,126	17,702
Interest and dividends payable	4,206	4,255
Taxes accrued	28,100	30,342
Regulatory liabilities	2,219	1,030
Other	7,637	8,760
Total current liabilities	60,288	62,089
Deferred credits and other liabilities
Deferred income taxes	108,052	100,681
Regulatory liabilities	93,974	84,623
Unamortized tax credits	15,994	15,406
Defined benefit pension and other postretirement benefit plans liability	75,005	69,893
Other	13,024	13,243
Total deferred credits and other liabilities	306,049	283,846
Contributions in aid of construction	97,210	95,298
Total capitalization and liabilities	975,541	954,515
MECO
Utility property, plant and equipment
Land	3,016	3,016
Plant and equipment	1,109,487	1,077,424
Less accumulated depreciation	(478,644)	(463,509)
Construction in progress	19,038	15,875
Utility property, plant and equipment, net	652,897	632,806
Nonutility property, plant and equipment, less accumulated depreciation	1,532	1,531
Total property, plant and equipment, net	654,429	634,337
Assets, Current [Abstract]
Cash and cash equivalents	2,048	5,385	633	153
Advances to affiliates	10,000	7,500
Customer accounts receivable, net	17,260	18,755
Accrued unbilled revenues, net	12,308	11,898
Other accounts receivable, net	1,416	1,674
Fuel oil stock, at average cost	10,962	13,451
Materials and supplies, at average cost	16,371	16,643
Prepayments and other	2,179	2,295
Regulatory assets	2,364	4,115
Total current assets	74,908	81,716
Other long-term assets
Regulatory assets	108,324	100,981
Unamortized debt expense	34	64
Other	13,592	13,062
Total other long-term assets	121,950	114,107
Total assets	851,287	830,160
Capitalization
Common stock equity	259,554	263,725	256,692	248,771
Cumulative preferred stock – not subject to mandatory redemption	5,000	5,000
Long-term debt, net	190,120	189,959
Total capitalization	454,674	458,684
Liabilities
Short-term borrowings-affiliate	0	0
Accounts payable	13,319	12,513
Interest and dividends payable	2,882	3,113
Taxes accrued	25,387	29,325
Regulatory liabilities	1,543	1,174
Other	12,501	13,194
Total current liabilities	55,632	59,319
Deferred credits and other liabilities
Deferred income taxes	100,911	87,706
Regulatory liabilities	31,845	30,683
Unamortized tax credits	15,123	14,730
Defined benefit pension and other postretirement benefit plans liability	80,263	74,060
Other	14,969	13,916
Total deferred credits and other liabilities	243,111	221,095
Contributions in aid of construction	97,870	91,062
Total capitalization and liabilities	851,287	830,160
Other subsidiaries
Assets, Current [Abstract]
Cash and cash equivalents	101	101	101	101
Total current assets	101	101
Other long-term assets
Total assets	101	101
Capitalization
Common stock equity	101	101	101	101
Total capitalization	101	101
Liabilities
Other		0
Total current liabilities		0
Deferred credits and other liabilities
Total capitalization and liabilities	101	101
Consolidating adjustments
Utility property, plant and equipment
Nonutility property, plant and equipment, less accumulated depreciation	0
Investment in wholly-owned subsidiaries, at equity	(550,946)	(556,528)
Assets, Current [Abstract]
Advances to affiliates	(13,500)	(23,000)
Other accounts receivable, net	(6,280)	(8,962)
Prepayments and other	(933)	(251)
Total current assets	(20,713)	(32,213)
Other long-term assets
Regulatory assets	0	0
Total other long-term assets	0	0
Total assets	(571,659)	(588,741)
Capitalization
Common stock equity	(550,946)	(556,528)	(538,639)	(523,674)
Total capitalization	(550,946)	(556,528)
Liabilities
Short-term borrowings-affiliate	(13,500)	(23,000)
Interest and dividends payable	(11)	(4)
Taxes accrued	(933)	(251)
Regulatory liabilities		0
Other	(6,269)	(8,958)
Total current liabilities	(20,713)	(32,213)
Deferred credits and other liabilities
Deferred income taxes	263	286
Regulatory liabilities	0	0
Defined benefit pension and other postretirement benefit plans liability	0
Other	(263)	(286)
Total deferred credits and other liabilities	0	0
Total capitalization and liabilities	(571,659)	(588,741)
HECO Consolidated
Utility property, plant and equipment
Land	53,153	52,792
Plant and equipment	6,605,732	6,315,698
Less accumulated depreciation	(2,369,282)	(2,266,004)
Construction in progress	211,742	175,309
Utility property, plant and equipment, net	4,501,345	4,277,795
Nonutility property, plant and equipment, less accumulated depreciation	7,407	7,272
Total property, plant and equipment, net	4,508,752	4,285,067
Investment in wholly-owned subsidiaries, at equity	0
Assets, Current [Abstract]
Cash and cash equivalents	74,286	24,449	13,762	62,825
Customer accounts receivable, net	123,688	132,778
Accrued unbilled revenues, net	91,693	84,509
Other accounts receivable, net	5,233	10,408
Fuel oil stock, at average cost	66,430	71,216
Materials and supplies, at average cost	53,679	54,429
Prepayments and other	23,100	36,640
Regulatory assets	66,032	72,231
Total current assets	504,141	486,660
Other long-term assets
Regulatory assets	891,419	824,500
Unamortized debt expense	208	497
Other	70,908	75,486
Total other long-term assets	962,535	900,483
Total assets	5,975,428	5,672,210
Capitalization
Common stock equity	1,799,787	1,728,325	$ 1,682,144	$ 1,593,564
Cumulative preferred stock – not subject to mandatory redemption	34,293	34,293
Long-term debt, net	1,319,260	1,278,702
Total capitalization	3,153,340	3,041,320
Liabilities
Accounts payable	117,814	114,846
Interest and dividends payable	22,838	23,111
Taxes accrued	172,730	191,084
Regulatory liabilities	3,762	2,204
Other	55,221	54,079
Total current liabilities	372,365	385,324
Deferred credits and other liabilities
Deferred income taxes	733,659	654,806
Regulatory liabilities	406,931	369,339
Unamortized tax credits	88,961	84,214
Defined benefit pension and other postretirement benefit plans liability	599,726	552,974
Other	76,921	78,146
Total deferred credits and other liabilities	1,906,198	1,739,479
Contributions in aid of construction	543,525	506,087
Total capitalization and liabilities	$ 5,975,428	$ 5,672,210