Electric utility segment - Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income (loss)	$ 32,843	$ 60,544	$ 39,134	$ 34,666	$ 45,107	$ 127,613	$ 44,601	$ 32,825	$ 167,187	$ 250,146	$ 161,767
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation of property, plant and equipment									200,658	194,273	183,966
Other amortization									21,340	10,473	11,619
Impairment of assets									0	0	6,021
Deferred income taxes									37,835	47,118	41,432
Allowance for equity funds used during construction									(12,483)	(8,325)	(6,928)
Other									(3,324)	(12,422)	1,672
Changes in assets and liabilities
Increase in fuel oil stock									(20,794)	4,786	34,830
Increase in regulatory assets									(17,256)	(18,273)	(24,182)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									20,685	39,109	(42,596)
Increase in defined benefit pension and other postretirement benefit plans liability									882	1,587	852
Net cash provided by operating activities									420,441	495,658	356,858
Cash flows from investing activities
Capital expenditures									(495,187)	(330,043)	(363,804)
Contributions in aid of construction									64,733	30,100	40,239
Other									6,468	856	7,940
Net cash used in investing activities									(815,299)	(736,465)	(705,724)
Cash flows from financing activities
Common stock dividends									(134,873)	(117,274)	(131,765)
Net proceeds from issuance of common stock									0	13,220	104,435
Proceeds from issuance of long-term debt									532,325	115,000	80,000
Funds transferred for redemption of special purpose revenue bonds									(465,000)	(75,000)	0
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									67,992	(103,063)	(15,909)
Other									(6,349)	2,197	2,427
Net cash used in financing activities									378,287	218,781	473,802
Net increase (decrease) in cash and equivalents									(16,571)	(22,026)	124,936
Hawaiian Electric Company, Inc (HECO)
Cash flows from operating activities
Net income (loss)									121,031	143,397	136,794
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									(38,157)	(42,491)	(43,020)
Common stock dividends received from subsidiaries									36,867	47,843	25,296
Depreciation of property, plant and equipment									130,889	126,086	117,682
Other amortization									2,398	2,979	4,678
Impairment of assets											4,573
Deferred income taxes									26,342	54,721	53,338
Allowance for equity funds used during construction									(10,896)	(6,659)	(5,641)
Other									(1,154)	(2,517)	8,687
Changes in assets and liabilities
Decrease in accounts receivable									1,817	10,175	15,652
Decrease (increase) in accrued unbilled revenues									(11,355)	(5,741)	29,733
Increase in fuel oil stock									(17,733)	2,216	25,060
Decrease (increase) in materials and supplies									1,603	993	2,233
Increase in regulatory assets									(8,395)	(16,161)	(20,356)
Increase (decrease) in accounts payable									23,519	(10,247)	(42,751)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									16,716	2,933	(50,382)
Increase in defined benefit pension and other postretirement benefit plans liability									709	599	870
Changes in other assets and liabilities									(16,213)	(11,682)	(24,197)
Net cash provided by operating activities									257,988	296,444	238,249
Cash flows from investing activities
Capital expenditures									(339,279)	(236,425)	(267,621)
Contributions in aid of construction									57,527	23,611	35,955
Advances from (to) affiliates									0	0	16,100
Other									(1,711)	1,932	924
Net cash used in investing activities									(283,463)	(210,882)	(214,642)
Cash flows from financing activities
Common stock dividends									(87,767)	(93,599)	(90,405)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(1,080)	(1,080)	(1,080)
Net proceeds from issuance of common stock									14,000	24,000
Proceeds from issuance of long-term debt									202,000	40,000	50,000
Funds transferred for redemption of special purpose revenue bonds									(162,000)
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									3,499	(9,500)	23,000
Other									(2,506)	(276)	(1,257)
Net cash used in financing activities									(33,854)	(40,455)	(19,742)
Net increase (decrease) in cash and equivalents									(59,329)	45,107	3,865
Cash and cash equivalents, beginning of period				61,388				16,281	61,388	16,281	12,416
Cash and cash equivalents, end of period	2,059				61,388				2,059	61,388	16,281
Hawaii Electric Light Company, Inc. (HELCO)
Cash flows from operating activities
Net income (loss)									20,680	21,789	21,289
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									0	0	0
Common stock dividends received from subsidiaries									0	0	0
Depreciation of property, plant and equipment									38,741	37,797	37,250
Other amortization									3,225	1,817	2,124
Impairment of assets											724
Deferred income taxes									3,954	7,027	8,295
Allowance for equity funds used during construction									(554)	(765)	(604)
Other									430	(750)	(1,949)
Changes in assets and liabilities
Decrease in accounts receivable									(359)	(718)	3,420
Decrease (increase) in accrued unbilled revenues									(2,376)	(1,033)	4,593
Increase in fuel oil stock									(469)	81	5,490
Decrease (increase) in materials and supplies									(661)	(515)	(201)
Increase in regulatory assets									(4,007)	(1,243)	(3,930)
Increase (decrease) in accounts payable									(3,547)	768	(6,425)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									7,961	2,645	(6,166)
Increase in defined benefit pension and other postretirement benefit plans liability									52	53	(161)
Changes in other assets and liabilities									(433)	(78)	(3,545)
Net cash provided by operating activities									62,637	66,875	60,204
Cash flows from investing activities
Capital expenditures									(52,077)	(51,344)	(48,645)
Contributions in aid of construction									4,293	3,412	2,160
Advances from (to) affiliates									3,500	12,000	(15,500)
Other									649	175	132
Net cash used in investing activities									(43,635)	(35,757)	(61,853)
Cash flows from financing activities
Common stock dividends									(24,796)	(22,507)	(10,021)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(534)	(534)	(534)
Net proceeds from issuance of common stock									0	0
Proceeds from issuance of long-term debt									28,000	0	25,000
Funds transferred for redemption of special purpose revenue bonds									(28,000)
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									0	0	(10,500)
Other									(396)	(10)	(226)
Net cash used in financing activities									(25,726)	(23,051)	3,719
Net increase (decrease) in cash and equivalents									(6,724)	8,067	2,070
Cash and cash equivalents, beginning of period				10,749				2,682	10,749	2,682	612
Cash and cash equivalents, end of period	4,025				10,749				4,025	10,749	2,682
Maui Electric Company, Limited (MECO)
Cash flows from operating activities
Net income (loss)									18,292	21,517	22,546
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									0	0	0
Common stock dividends received from subsidiaries									0	0	0
Depreciation of property, plant and equipment									23,154	23,178	22,448
Other amortization									2,875	2,139	2,137
Impairment of assets											724
Deferred income taxes									8,004	12,661	13,707
Allowance for equity funds used during construction									(1,033)	(901)	(683)
Other									(342)	(433)	(222)
Changes in assets and liabilities
Decrease in accounts receivable									45	1,776	4,617
Decrease (increase) in accrued unbilled revenues									(1,630)	(410)	5,767
Increase in fuel oil stock									(2,241)	2,489	4,280
Decrease (increase) in materials and supplies									(1,660)	272	789
Increase in regulatory assets									(4,854)	(869)	104
Increase (decrease) in accounts payable									5,762	(1,135)	(5,379)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									5,362	(3,478)	(6,548)
Increase in defined benefit pension and other postretirement benefit plans liability									(157)	(168)	416
Changes in other assets and liabilities									166	(2,272)	(4,554)
Net cash provided by operating activities									51,743	54,366	60,149
Cash flows from investing activities
Capital expenditures									(50,242)	(32,668)	(33,895)
Contributions in aid of construction									2,913	3,077	2,124
Advances from (to) affiliates									(2,000)	(2,500)	(7,500)
Other									400	31	84
Net cash used in investing activities									(48,929)	(32,060)	(39,187)
Cash flows from financing activities
Common stock dividends									(11,946)	(25,261)	(15,175)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(381)	(381)	(381)
Net proceeds from issuance of common stock									4,800	0
Proceeds from issuance of long-term debt									85,000	0	5,000
Funds transferred for redemption of special purpose revenue bonds									(75,000)
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									0	0	(5,600)
Other									(1,003)	(1)	(54)
Net cash used in financing activities									1,470	(25,643)	(16,210)
Net increase (decrease) in cash and equivalents									4,284	(3,337)	4,752
Cash and cash equivalents, beginning of period				2,048				5,385	2,048	5,385	633
Cash and cash equivalents, end of period	6,332				2,048				6,332	2,048	5,385
Other subsidiaries
Cash flows from operating activities
Net income (loss)									0	0	0
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									0	0	0
Common stock dividends received from subsidiaries									0	0	0
Depreciation of property, plant and equipment									0	0	0
Other amortization									0	0	0
Impairment of assets											0
Deferred income taxes									0	0	0
Allowance for equity funds used during construction									0	0	0
Other									0	0	0
Changes in assets and liabilities
Decrease in accounts receivable									0	0	0
Decrease (increase) in accrued unbilled revenues									0	0	0
Increase in fuel oil stock									0	0	0
Decrease (increase) in materials and supplies									0	0	0
Increase in regulatory assets									0	0	0
Increase (decrease) in accounts payable									0	0	0
Change in prepaid and accrued income taxes, tax credits and revenue taxes									0	0	0
Increase in defined benefit pension and other postretirement benefit plans liability									0	0	0
Changes in other assets and liabilities									0	0	0
Net cash provided by operating activities									0	0	0
Cash flows from investing activities
Capital expenditures									0	0	0
Contributions in aid of construction									0	0	0
Advances from (to) affiliates									0	0	0
Other									0	0	0
Net cash used in investing activities									0	0	0
Cash flows from financing activities
Common stock dividends									0	0	0
Preferred stock dividends of Hawaiian Electric and subsidiaries									0	0	0
Net proceeds from issuance of common stock									0	0
Proceeds from issuance of long-term debt									0	0	0
Funds transferred for redemption of special purpose revenue bonds									0
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									0	0	0
Other									0	0	0
Net cash used in financing activities									0	0	0
Net increase (decrease) in cash and equivalents									0	0	0
Cash and cash equivalents, beginning of period				101				101	101	101	101
Cash and cash equivalents, end of period	101				101				101	101	101
Consolidating adjustments
Cash flows from operating activities
Net income (loss)									(38,057)	(42,391)	(42,920)
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									38,057	42,391	42,920
Common stock dividends received from subsidiaries									(36,742)	(47,768)	(25,196)
Depreciation of property, plant and equipment									0	0	0
Other amortization									0	0	0
Impairment of assets											0
Deferred income taxes									(263)	(23)	286
Allowance for equity funds used during construction									0	0	0
Other									0	0	0
Changes in assets and liabilities
Decrease in accounts receivable									1,411	(2,682)	38
Decrease (increase) in accrued unbilled revenues									0	0	0
Increase in fuel oil stock									0	0	0
Decrease (increase) in materials and supplies									0	0	0
Increase in regulatory assets									0	0	0
Increase (decrease) in accounts payable									0	0	0
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(177)	23	0
Increase in defined benefit pension and other postretirement benefit plans liability									0	0	0
Changes in other assets and liabilities									(1,411)	2,682	(324)
Net cash provided by operating activities									(37,182)	(47,768)	(25,196)
Cash flows from investing activities
Capital expenditures									0	0	0
Contributions in aid of construction									0	0	0
Advances from (to) affiliates									(1,500)	(9,500)	6,900
Other									5,240	0	0
Net cash used in investing activities									3,740	(9,500)	6,900
Cash flows from financing activities
Common stock dividends									36,742	47,768	25,196
Preferred stock dividends of Hawaiian Electric and subsidiaries									0	0	0
Net proceeds from issuance of common stock									(4,800)	0
Proceeds from issuance of long-term debt									0	0	0
Funds transferred for redemption of special purpose revenue bonds									0
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									1,500	9,500	(6,900)
Other									0	0	0
Net cash used in financing activities									33,442	57,268	18,296
Net increase (decrease) in cash and equivalents									0	0	0
Cash and cash equivalents, beginning of period				0				0	0	0	0
Cash and cash equivalents, end of period	0				0				0	0	0
HECO Consolidated
Cash flows from operating activities
Net income (loss)	25,854	$ 47,985	$ 26,143	21,964	34,618	$ 47,472	$ 36,356	25,866	121,946	144,312	137,709
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									(100)	(100)	(100)
Common stock dividends received from subsidiaries									125	75	100
Depreciation of property, plant and equipment									192,784	187,061	177,380
Other amortization									8,498	6,935	8,939
Impairment of assets									0	0	6,021
Deferred income taxes									38,037	74,386	75,626
Allowance for equity funds used during construction									(12,483)	(8,325)	(6,928)
Other									(1,066)	(3,700)	6,516
Changes in assets and liabilities
Decrease in accounts receivable									2,914	8,551	23,727
Decrease (increase) in accrued unbilled revenues									(15,361)	(7,184)	40,093
Increase in fuel oil stock									(20,443)	4,786	34,830
Decrease (increase) in materials and supplies									(718)	750	2,821
Increase in regulatory assets									(17,256)	(18,273)	(24,182)
Increase (decrease) in accounts payable									25,734	(10,614)	(54,555)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									29,862	2,123	(63,096)
Increase in defined benefit pension and other postretirement benefit plans liability									604	484	1,125
Changes in other assets and liabilities									(17,891)	(11,350)	(32,620)
Net cash provided by operating activities									335,186	369,917	333,406
Cash flows from investing activities
Capital expenditures									(441,598)	(320,437)	(350,161)
Contributions in aid of construction									64,733	30,100	40,239
Advances from (to) affiliates									0	0	0
Other									4,578	2,138	1,140
Net cash used in investing activities									(372,287)	(288,199)	(308,782)
Cash flows from financing activities
Common stock dividends									(87,767)	(93,599)	(90,405)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(1,995)	(1,995)	(1,995)
Net proceeds from issuance of common stock									14,000	24,000	0
Proceeds from issuance of long-term debt									315,000	40,000	80,000
Funds transferred for redemption of special purpose revenue bonds									(265,000)	0	0
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									4,999	0	0
Other									(3,905)	(287)	(1,537)
Net cash used in financing activities									(24,668)	(31,881)	(13,937)
Net increase (decrease) in cash and equivalents									(61,769)	49,837	10,687
Cash and cash equivalents, beginning of period				$ 74,286				$ 24,449	74,286	24,449	13,762
Cash and cash equivalents, end of period	$ 12,517				$ 74,286				$ 12,517	$ 74,286	$ 24,449