Electric utility segment - Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Net income (loss)	$ 50,046	$ 66,371	$ 46,527	$ 40,720	$ 32,843	$ 60,544	$ 39,134	$ 34,666	$ 203,664	$ 167,187	$ 250,146
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation of property, plant and equipment									214,036	200,658	194,273
Other amortization									41,593	21,340	10,473
Deferred income taxes									(9,368)	37,835	47,118
Allowance for equity funds used during construction									(10,877)	(12,483)	(8,325)
Other									(4,219)	(3,324)	(12,422)
Changes in assets and liabilities
Decrease (increase) in fuel oil stock									7,054	(20,794)	4,786
Decrease (increase) in regulatory assets									9,252	(17,256)	(18,273)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									29,429	20,685	39,109
Increase in defined benefit pension and other postretirement benefit plans liability									20,871	882	1,587
Net cash provided by operating activities									499,312	420,441	495,658
Cash flows from investing activities
Capital expenditures									(537,369)	(495,187)	(330,043)
Contributions in aid of construction									30,599	64,733	30,100
Other, net									13,945	6,468	856
Net cash used in investing activities									(792,059)	(815,299)	(736,465)
Cash flows from financing activities
Common stock dividends									(134,987)	(134,873)	(117,274)
Net proceeds from issuance of common stock									0	0	13,220
Proceeds from issuance of long-term debt									250,000	532,325	115,000
Repayment of long-term debt and funds transferred for redemption of special purpose revenue bonds									(53,887)	(465,000)	(75,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									(18,999)	67,992	(103,063)
Proceeds from other bank borrowings									696,000	59,500	180,835
Other									(1,603)	(6,349)	2,197
Net cash used in financing activities									200,074	378,287	218,781
Net decrease in cash and equivalents									(92,673)	(16,571)	(22,026)
Hawaiian Electric
Cash flows from operating activities
Net income (loss)									144,733	121,031	143,397
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									(45,493)	(38,157)	(42,491)
Common stock dividends received from subsidiaries									27,408	36,867	47,843
Depreciation of property, plant and equipment									137,410	130,889	126,086
Other amortization									20,956	2,398	2,979
Deferred income taxes									(9,806)	26,342	54,721
Allowance for equity funds used during construction									(9,208)	(10,896)	(6,659)
Other									(1,033)	(1,154)	(2,517)
Changes in assets and liabilities
Decrease (increase) in accounts receivable									(51,656)	1,817	10,175
Increase in accrued unbilled revenues									(10,884)	(11,355)	(5,741)
Decrease (increase) in fuel oil stock									10,710	(17,733)	2,216
Decrease (increase) in materials and supplies									(1,966)	1,603	993
Decrease (increase) in regulatory assets									12,192	(8,395)	(16,161)
Increase (decrease) in accounts payable									14,748	23,519	(10,247)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									24,438	16,716	2,933
Increase in defined benefit pension and other postretirement benefit plans liability									17,178	709	599
Changes in other assets and liabilities									18,484	(16,213)	(11,682)
Net cash provided by operating activities									298,211	257,988	296,444
Cash flows from investing activities
Capital expenditures									(330,531)	(339,279)	(236,425)
Contributions in aid of construction									24,828	57,527	23,611
Advances from (to) affiliates									0	0	0
Other, net									3,226	(1,711)	1,932
Net cash used in investing activities									(302,477)	(283,463)	(210,882)
Cash flows from financing activities
Common stock dividends									(103,305)	(87,767)	(93,599)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(1,080)	(1,080)	(1,080)
Net proceeds from issuance of common stock									70,700	14,000	24,000
Proceeds from issuance of long-term debt									75,000	202,000	40,000
Repayment of long-term debt and funds transferred for redemption of special purpose revenue bonds									(30,000)	(162,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									(16,999)	3,499	(9,500)
Proceeds from other bank borrowings									25,000
Other									(377)	(2,506)	(276)
Net cash used in financing activities									18,939	(33,854)	(40,455)
Net decrease in cash and equivalents									14,673	(59,329)	45,107
Cash and cash equivalents, beginning of period				2,059				61,388	2,059	61,388	16,281
Cash and cash equivalents, end of period	16,732				2,059				16,732	2,059	61,388
Hawaii Electric Light Company, Inc. (HELCO)
Cash flows from operating activities
Net income (loss)									25,015	20,680	21,789
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									40,235	38,741	37,797
Other amortization									5,069	3,225	1,817
Deferred income taxes									(341)	3,954	7,027
Allowance for equity funds used during construction									(478)	(554)	(765)
Other									(213)	430	(750)
Changes in assets and liabilities
Decrease (increase) in accounts receivable									(4,867)	(359)	(718)
Increase in accrued unbilled revenues									(1,111)	(2,376)	(1,033)
Decrease (increase) in fuel oil stock									(2,329)	(469)	81
Decrease (increase) in materials and supplies									886	(661)	(515)
Decrease (increase) in regulatory assets									71	(4,007)	(1,243)
Increase (decrease) in accounts payable									6,104	(3,547)	768
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(2,118)	7,961	2,645
Increase in defined benefit pension and other postretirement benefit plans liability									(760)	52	53
Changes in other assets and liabilities									8,186	(433)	(78)
Net cash provided by operating activities									73,349	62,637	66,875
Cash flows from investing activities
Capital expenditures									(54,553)	(52,077)	(51,344)
Contributions in aid of construction									3,499	4,293	3,412
Advances from (to) affiliates									0	3,500	12,000
Other, net									1,182	649	175
Net cash used in investing activities									(49,872)	(43,635)	(35,757)
Cash flows from financing activities
Common stock dividends									(15,289)	(24,796)	(22,507)
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									15,000	28,000	0
Repayment of long-term debt and funds transferred for redemption of special purpose revenue bonds									(11,000)	(28,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									0	0	0
Proceeds from other bank borrowings									0
Other									(56)	(396)	(10)
Net cash used in financing activities									(11,879)	(25,726)	(23,051)
Net decrease in cash and equivalents									11,598	(6,724)	8,067
Cash and cash equivalents, beginning of period				4,025				10,749	4,025	10,749	2,682
Cash and cash equivalents, end of period	15,623				4,025				15,623	4,025	10,749
Maui Electric Company, Limited (MECO)
Cash flows from operating activities
Net income (loss)									21,293	18,292	21,517
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									25,981	23,154	23,178
Other amortization									577	2,875	2,139
Deferred income taxes									2,165	8,004	12,661
Allowance for equity funds used during construction									(1,191)	(1,033)	(901)
Other									(324)	(342)	(433)
Changes in assets and liabilities
Decrease (increase) in accounts receivable									(8,614)	45	1,776
Increase in accrued unbilled revenues									(2,689)	(1,630)	(410)
Decrease (increase) in fuel oil stock									(1,443)	(2,241)	2,489
Decrease (increase) in materials and supplies									273	(1,660)	272
Decrease (increase) in regulatory assets									(3,011)	(4,854)	(869)
Increase (decrease) in accounts payable									3,506	5,762	(1,135)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									3,047	5,362	(3,478)
Increase in defined benefit pension and other postretirement benefit plans liability									2,328	(157)	(168)
Changes in other assets and liabilities									7,794	166	(2,272)
Net cash provided by operating activities									49,692	51,743	54,366
Cash flows from investing activities
Capital expenditures									(60,779)	(50,242)	(32,668)
Contributions in aid of construction									2,272	2,913	3,077
Advances from (to) affiliates									12,000	(2,000)	(2,500)
Other, net									3,843	400	31
Net cash used in investing activities									(42,664)	(48,929)	(32,060)
Cash flows from financing activities
Common stock dividends									(12,019)	(11,946)	(25,261)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(381)	(381)	(381)
Net proceeds from issuance of common stock									1,500	4,800	0
Proceeds from issuance of long-term debt									10,000	85,000	0
Repayment of long-term debt and funds transferred for redemption of special purpose revenue bonds									(9,000)	(75,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									0	0	0
Proceeds from other bank borrowings									0
Other									(39)	(1,003)	(1)
Net cash used in financing activities									(9,939)	1,470	(25,643)
Net decrease in cash and equivalents									(2,911)	4,284	(3,337)
Cash and cash equivalents, beginning of period				6,332				2,048	6,332	2,048	5,385
Cash and cash equivalents, end of period	3,421				6,332				3,421	6,332	2,048
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
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 (increase) in accounts receivable									0	0	0
Increase in accrued unbilled revenues									0	0	0
Decrease (increase) in fuel oil stock									0	0	0
Decrease (increase) in materials and supplies									0	0	0
Decrease (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, net									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	0
Proceeds from issuance of long-term debt									0	0	0
Repayment of long-term debt and funds transferred for redemption of special purpose revenue bonds									0	0
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									0	0	0
Proceeds from other bank borrowings									0
Other									0	0	0
Net cash used in financing activities									0	0	0
Net 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)									(45,393)	(38,057)	(42,391)
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									45,393	38,057	42,391
Common stock dividends received from subsidiaries									(27,308)	(36,742)	(47,768)
Depreciation of property, plant and equipment									0	0	0
Other amortization									0	0	0
Deferred income taxes									0	(263)	(23)
Allowance for equity funds used during construction									0	0	0
Other									0	0	0
Changes in assets and liabilities
Decrease (increase) in accounts receivable									14,220	1,411	(2,682)
Increase in accrued unbilled revenues									0	0	0
Decrease (increase) in fuel oil stock									0	0	0
Decrease (increase) in materials and supplies									0	0	0
Decrease (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									(331)	(177)	23
Increase in defined benefit pension and other postretirement benefit plans liability									0	0	0
Changes in other assets and liabilities									(14,220)	(1,411)	2,682
Net cash provided by operating activities									(27,639)	(37,182)	(47,768)
Cash flows from investing activities
Capital expenditures									0	0	0
Contributions in aid of construction									0	0	0
Advances from (to) affiliates									(12,000)	(1,500)	(9,500)
Other, net									1,831	5,240	0
Net cash used in investing activities									(10,169)	3,740	(9,500)
Cash flows from financing activities
Common stock dividends									27,308	36,742	47,768
Preferred stock dividends of Hawaiian Electric and subsidiaries									0	0	0
Net proceeds from issuance of common stock									(1,500)	(4,800)	0
Proceeds from issuance of long-term debt									0	0	0
Repayment of long-term debt and funds transferred for redemption of special purpose revenue bonds									0	0
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									12,000	1,500	9,500
Proceeds from other bank borrowings									0
Other									0	0	0
Net cash used in financing activities									37,808	33,442	57,268
Net 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)	35,796	$ 50,210	$ 31,668	27,974	25,854	$ 47,985	$ 26,143	21,964	145,648	121,946	144,312
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									(100)	(100)	(100)
Common stock dividends received from subsidiaries									100	125	75
Depreciation of property, plant and equipment									203,626	192,784	187,061
Other amortization									26,602	8,498	6,935
Deferred income taxes									(7,982)	38,037	74,386
Allowance for equity funds used during construction									(10,877)	(12,483)	(8,325)
Other									(1,570)	(1,066)	(3,700)
Changes in assets and liabilities
Decrease (increase) in accounts receivable									(50,917)	2,914	8,551
Increase in accrued unbilled revenues									(14,684)	(15,361)	(7,184)
Decrease (increase) in fuel oil stock									6,938	(20,443)	4,786
Decrease (increase) in materials and supplies									(807)	(718)	750
Decrease (increase) in regulatory assets									9,252	(17,256)	(18,273)
Increase (decrease) in accounts payable									24,358	25,734	(10,614)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									25,036	29,862	2,123
Increase in defined benefit pension and other postretirement benefit plans liability									18,746	604	484
Changes in other assets and liabilities									20,244	(17,891)	(11,350)
Net cash provided by operating activities									393,613	335,186	369,917
Cash flows from investing activities
Capital expenditures									(445,863)	(441,598)	(320,437)
Contributions in aid of construction									30,599	64,733	30,100
Advances from (to) affiliates									0	0	0
Other, net									10,082	4,578	2,138
Net cash used in investing activities									(405,182)	(372,287)	(288,199)
Cash flows from financing activities
Common stock dividends									(103,305)	(87,767)	(93,599)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(1,995)	(1,995)	(1,995)
Net proceeds from issuance of common stock									70,700	14,000	24,000
Proceeds from issuance of long-term debt									100,000	315,000	40,000
Repayment of long-term debt and funds transferred for redemption of special purpose revenue bonds									(50,000)	(265,000)	0
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									(4,999)	4,999	0
Proceeds from other bank borrowings									25,000
Other									(472)	(3,905)	(287)
Net cash used in financing activities									34,929	(24,668)	(31,881)
Net decrease in cash and equivalents									23,360	(61,769)	49,837
Cash and cash equivalents, beginning of period				$ 12,517				$ 74,286	12,517	74,286	24,449
Cash and cash equivalents, end of period	$ 35,877				$ 12,517				$ 35,877	$ 12,517	$ 74,286