Electric utility segment - Consolidating Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net income (loss)	$ 50,958	$ 65,503	$ 49,360	$ 33,893	$ 66,736	$ 63,890	$ 42,985	$ 46,161	$ 199,714	$ 219,772	$ 203,664
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation of property, plant and equipment									238,114	229,858	214,036
Other amortization									52,664	48,255	41,593
Deferred income taxes									(1,706)	(15,085)	(9,368)
Bad debt expense									2,115	2,150	2,205
Allowance for equity funds used during construction									(8,768)	(11,987)	(10,877)
Other									1,366	18,568	(521)
Changes in assets and liabilities
Decrease in fuel oil stock									34,202	(11,493)	7,054
Decrease in regulatory assets									1,007	71,262	9,252
Increase (decrease) in regulatory liabilities									(16,562)	1,953	37,358
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(35,610)	(27,538)	29,429
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(2,029)	(4,482)	20,871
Net cash provided by operating activities									429,407	512,470	499,312
Cash flows from investing activities
Capital expenditures									(383,895)	(457,520)	(537,369)
Other, net									3,412	13,291	14,061
Net cash used in investing activities									(1,413,648)	(541,709)	(792,059)
Cash flows from financing activities
Common stock dividends									(144,096)	(139,463)	(134,987)
Proceeds from issuance of long-term debt									415,997	289,349	250,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									(178,969)	(287,285)	(53,887)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									(71,219)	86,718	(18,999)
Net increase (decrease) in other bank borrowings with original maturities of three months or less									(25,440)	5,070	71,556
Proceeds from issuance of short-term debt									165,000	75,000	25,000
Repayment of short-term debt									(150,000)	(50,000)	(50,000)
Other									(3,203)	(1,836)	(1,603)
Net cash used in financing activities									1,115,535	87,716	200,074
Net decrease in cash and equivalents									131,294	58,477	(92,673)
Cash, cash equivalents and restricted cash, January 1				227,685				169,208	227,685	169,208	261,881
Cash, cash equivalents and restricted cash, December 31	358,979				227,685				358,979	227,685	169,208
Less: Restricted cash	(17,558)				(30,872)				(17,558)	(30,872)	0
Cash and cash equivalents	341,421				196,813				341,421	196,813	169,208
Hawaiian Electric (parent only)
Cash flows from operating activities
Net income (loss)									197,824	217,882	201,774
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation of property, plant and equipment									485	570	597
Changes in assets and liabilities
Net cash provided by operating activities									134,363	131,120	135,470
Cash flows from investing activities
Capital expenditures									(20)	(47)	(143)
Other, net									2,435	(1,001)	140
Net cash used in investing activities									(17,530)	(41,170)	(92,569)
Cash flows from financing activities
Common stock dividends									(144,096)	(139,463)	(134,987)
Proceeds from issuance of long-term debt									50,000	0	150,000
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									(32,232)	47,731	(14,000)
Proceeds from issuance of short-term debt									65,000	0	0
Repayment of short-term debt									(50,000)	0	(50,000)
Other									(459)	(10)	(848)
Net cash used in financing activities									(117,487)	(92,739)	(50,861)
Net decrease in cash and equivalents									(654)	(2,789)	(7,960)
Cash, cash equivalents and restricted cash, January 1				953				3,742	953	3,742	11,702
Cash, cash equivalents and restricted cash, December 31	299				953				299	953	3,742
Hawaiian Electric Company, Inc. and Subsidiaries
Cash flows from operating activities
Net income (loss)	43,540	$ 60,563	$ 42,828	24,404	45,860	$ 47,277	$ 33,073	32,625	171,335	158,835	145,648
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings of subsidiaries									0	(37)	(100)
Common stock dividends received from subsidiaries									0	35	100
Depreciation of property, plant and equipment									222,733	215,731	203,626
Other amortization									33,746	29,631	26,602
Deferred income taxes									3,151	(16,284)	(7,982)
State refundable credit									(9,961)	(8,369)	(6,239)
Bad debt expense									2,115	2,150	2,205
Allowance for equity funds used during construction									(8,768)	(11,987)	(10,877)
Accrued environmental reserve									6,556	406	273
Other									2,610	27,459	4,669
Changes in assets and liabilities
Decrease (increase) in accounts receivable									(7,286)	18,822	(53,086)
Decrease (increase) in accrued unbilled revenues									15,285	4,495	(14,720)
Decrease in fuel oil stock									33,699	(12,002)	6,938
Increase in materials and supplies									(6,642)	(5,498)	(807)
Decrease in regulatory assets									1,007	71,262	9,252
Increase (decrease) in regulatory liabilities									(16,562)	1,953	37,358
Increase (decrease) in accounts payable									(33,129)	(2,051)	24,358
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(37,180)	(28,523)	25,036
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(4,306)	(4,448)	18,746
Changes in other assets and liabilities									(31,852)	(17,624)	(17,387)
Net cash provided by operating activities									336,551	423,956	393,613
Cash flows from investing activities
Capital expenditures									(350,864)	(419,898)	(415,264)
Advances from (to) affiliates									0	0	0
Other, net									6,070	11,374	10,082
Net cash used in investing activities									(344,794)	(408,524)	(405,182)
Cash flows from financing activities
Common stock dividends									(107,134)	(101,252)	(103,305)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(1,995)	(1,995)	(1,995)
Proceeds from issuance of common stock									34,000	35,500	70,700
Proceeds from issuance of long-term debt									255,000	280,000	100,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									(109,000)	(283,546)	(50,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									(38,987)	38,987	(4,999)
Net increase (decrease) in other bank borrowings with original maturities of three months or less										38,987
Proceeds from issuance of short-term debt									100,000	75,000	25,000
Repayment of short-term debt									(100,000)	(50,000)	0
Other									(2,209)	(2,109)	(472)
Net cash used in financing activities									29,675	(9,415)	34,929
Net decrease in cash and equivalents									21,432	6,017	23,360
Cash, cash equivalents and restricted cash, January 1				41,894				35,877	41,894	35,877	12,517
Cash, cash equivalents and restricted cash, December 31	63,326				41,894				63,326	41,894	35,877
Less: Restricted cash	(15,966)				(30,872)				(15,966)	(30,872)	0
Cash and cash equivalents	47,360				11,022				47,360	11,022	35,877
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Hawaiian Electric (parent only)
Cash flows from operating activities
Net income (loss)									170,420	157,920	144,733
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings of subsidiaries									(47,504)	(43,204)	(45,493)
Common stock dividends received from subsidiaries									30,704	32,783	27,408
Depreciation of property, plant and equipment									151,387	143,470	137,410
Other amortization									24,511	23,351	20,956
Deferred income taxes									2,130	(13,547)	(9,806)
State refundable credit									(6,668)	(6,245)	(4,941)
Bad debt expense									1,042	1,236	1,388
Allowance for equity funds used during construction									(7,335)	(9,955)	(9,208)
Accrued environmental reserve									6,556	406	273
Other									1,201	27,575	3,908
Changes in assets and liabilities
Decrease (increase) in accounts receivable									(8,093)	24,150	(53,020)
Decrease (increase) in accrued unbilled revenues									8,832	4,902	(10,908)
Decrease in fuel oil stock									30,226	(14,741)	10,710
Increase in materials and supplies									(3,910)	(4,585)	(1,966)
Decrease in regulatory assets									8,526	55,494	12,192
Increase (decrease) in regulatory liabilities									(5,490)	102	26,540
Increase (decrease) in accounts payable									(26,093)	4,687	14,748
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(25,757)	(24,900)	24,438
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(3,092)	(3,033)	17,178
Changes in other assets and liabilities									(21,124)	(15,747)	(8,329)
Net cash provided by operating activities									280,469	340,119	298,211
Cash flows from investing activities
Capital expenditures									(229,127)	(311,538)	(305,703)
Advances from (to) affiliates									1,000	(27,700)	0
Other, net									(14,340)	5,241	3,226
Net cash used in investing activities									(242,467)	(333,997)	(302,477)
Cash flows from financing activities
Common stock dividends									(107,134)	(101,252)	(103,305)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(1,080)	(1,080)	(1,080)
Proceeds from issuance of common stock									34,000	35,500	70,700
Proceeds from issuance of long-term debt									205,000	190,000	75,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									(95,000)	(183,546)	(30,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									(46,987)		(16,999)
Net increase (decrease) in other bank borrowings with original maturities of three months or less										46,987
Proceeds from issuance of short-term debt									100,000	75,000	25,000
Repayment of short-term debt									(100,000)	(50,000)
Other									(1,618)	(1,475)	(377)
Net cash used in financing activities									(12,819)	10,134	18,939
Net decrease in cash and equivalents									25,183	16,256	14,673
Cash, cash equivalents and restricted cash, January 1				32,988				16,732	32,988	16,732	2,059
Cash, cash equivalents and restricted cash, December 31	58,171				32,988				58,171	32,988	16,732
Less: Restricted cash	(15,966)				(30,749)				(15,966)	(30,749)
Cash and cash equivalents	42,205				2,239				42,205	2,239
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | HELCO
Cash flows from operating activities
Net income (loss)									28,027	21,351	25,015
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings of subsidiaries									0	0	0
Common stock dividends received from subsidiaries									0	0	0
Depreciation of property, plant and equipment									39,041	41,812	40,235
Other amortization									5,090	4,810	5,069
Deferred income taxes									(463)	(2,383)	(341)
State refundable credit									(1,593)	(559)	(547)
Bad debt expense									620	470	600
Allowance for equity funds used during construction									(543)	(816)	(478)
Accrued environmental reserve									0	0	0
Other									1,322	(61)	334
Changes in assets and liabilities
Decrease (increase) in accounts receivable									(3,349)	2,858	(5,457)
Decrease (increase) in accrued unbilled revenues									3,327	(22)	(1,121)
Decrease in fuel oil stock									430	2,126	(2,329)
Increase in materials and supplies									(1,583)	(1,158)	886
Decrease in regulatory assets									(2,908)	9,218	71
Increase (decrease) in regulatory liabilities									(4,489)	(1,558)	5,380
Increase (decrease) in accounts payable									(1,819)	(3,160)	6,104
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(5,483)	(893)	(2,118)
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(643)	(762)	(760)
Changes in other assets and liabilities									(8,864)	(6,152)	2,806
Net cash provided by operating activities									46,120	65,121	73,349
Cash flows from investing activities
Capital expenditures									(64,346)	(49,811)	(51,054)
Advances from (to) affiliates									8,000	(8,000)	0
Other, net									1,032	297	1,182
Net cash used in investing activities									(55,314)	(57,514)	(49,872)
Cash flows from financing activities
Common stock dividends									(16,320)	(17,680)	(15,289)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(534)	(534)	(534)
Proceeds from issuance of common stock									7,500	0	0
Proceeds from issuance of long-term debt									10,000	72,500	15,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									(14,000)	(70,000)	(11,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									18,800		0
Net increase (decrease) in other bank borrowings with original maturities of three months or less										0
Proceeds from issuance of short-term debt									0	0	0
Repayment of short-term debt									0	0
Other									(214)	(508)	(56)
Net cash used in financing activities									5,232	(16,222)	(11,879)
Net decrease in cash and equivalents									(3,962)	(8,615)	11,598
Cash, cash equivalents and restricted cash, January 1				7,008				15,623	7,008	15,623	4,025
Cash, cash equivalents and restricted cash, December 31	3,046				7,008				3,046	7,008	15,623
Less: Restricted cash	0				(123)				0	(123)
Cash and cash equivalents	3,046				6,885				3,046	6,885
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Maui Electric
Cash flows from operating activities
Net income (loss)									20,392	22,731	21,293
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings of subsidiaries									0	0	0
Common stock dividends received from subsidiaries									0	0	0
Depreciation of property, plant and equipment									32,305	30,449	25,981
Other amortization									4,145	1,470	577
Deferred income taxes									1,484	(354)	2,165
State refundable credit									(1,700)	(1,565)	(751)
Bad debt expense									453	444	217
Allowance for equity funds used during construction									(890)	(1,216)	(1,191)
Accrued environmental reserve									0	0	0
Other									87	(55)	427
Changes in assets and liabilities
Decrease (increase) in accounts receivable									(1,343)	3,029	(8,829)
Decrease (increase) in accrued unbilled revenues									3,126	(385)	(2,691)
Decrease in fuel oil stock									3,043	613	(1,443)
Increase in materials and supplies									(1,149)	245	273
Decrease in regulatory assets									(4,611)	6,550	(3,011)
Increase (decrease) in regulatory liabilities									(6,583)	3,409	5,438
Increase (decrease) in accounts payable									(5,217)	(3,578)	3,506
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(5,998)	(3,097)	3,047
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(571)	(653)	2,328
Changes in other assets and liabilities									3,635	(6,940)	2,356
Net cash provided by operating activities									40,608	51,097	49,692
Cash flows from investing activities
Capital expenditures									(57,391)	(58,549)	(58,507)
Advances from (to) affiliates									0	0	12,000
Other, net									960	1,303	3,843
Net cash used in investing activities									(56,431)	(57,246)	(42,664)
Cash flows from financing activities
Common stock dividends									(14,384)	(15,068)	(12,019)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(381)	(381)	(381)
Proceeds from issuance of common stock									11,000	4,900	1,500
Proceeds from issuance of long-term debt									40,000	17,500	10,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									0	(30,000)	(9,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									(19,800)		0
Net increase (decrease) in other bank borrowings with original maturities of three months or less										27,700
Proceeds from issuance of short-term debt									0	0	0
Repayment of short-term debt									0	0
Other									(377)	(126)	(39)
Net cash used in financing activities									16,058	4,525	(9,939)
Net decrease in cash and equivalents									235	(1,624)	(2,911)
Cash, cash equivalents and restricted cash, January 1				1,797				3,421	1,797	3,421	6,332
Cash, cash equivalents and restricted cash, December 31	2,032				1,797				2,032	1,797	3,421
Less: Restricted cash	0				0				0	0
Cash and cash equivalents	2,032				1,797				2,032	1,797
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | 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 of subsidiaries									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
State refundable credit									0	0	0
Bad debt expense									0	0	0
Allowance for equity funds used during construction									0	0	0
Accrued environmental reserve									0	0	0
Other									0	0	0
Changes in assets and liabilities
Decrease (increase) in accounts receivable									0	0	0
Decrease (increase) in accrued unbilled revenues									0	0	0
Decrease in fuel oil stock									0	0	0
Increase in materials and supplies									0	0	0
Decrease in regulatory assets									0	0	0
Increase (decrease) in regulatory liabilities											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 (decrease) 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
Advances from (to) affiliates									0	0	0
Other, net									(24)	0	0
Net cash used in investing activities									(24)	0	0
Cash flows from financing activities
Common stock dividends									0	0	0
Preferred stock dividends of Hawaiian Electric and subsidiaries									0	0	0
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 repayment of long-term debt									0	0	0
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									0		0
Net increase (decrease) in other bank borrowings with original maturities of three months or less										0
Proceeds from issuance of short-term debt									0	0	0
Repayment of short-term debt									0	0
Other									0	0	0
Net cash used in financing activities									0	0	0
Net decrease in cash and equivalents									(24)	0	0
Cash, cash equivalents and restricted cash, January 1				101				101	101	101	101
Cash, cash equivalents and restricted cash, December 31	77				101				77	101	101
Less: Restricted cash	0				0				0	0
Cash and cash equivalents	77				101				77	101
Hawaiian Electric Company, Inc. and Subsidiaries | Consolidating Adjustments
Cash flows from operating activities
Net income (loss)									(47,504)	(43,167)	(45,393)
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings of subsidiaries									47,504	43,167	45,393
Common stock dividends received from subsidiaries									(30,704)	(32,748)	(27,308)
Depreciation of property, plant and equipment									0	0	0
Other amortization									0	0	0
Deferred income taxes									0	0	0
State refundable credit									0	0	0
Bad debt expense									0	0	0
Allowance for equity funds used during construction									0	0	0
Accrued environmental reserve									0	0	0
Other									0	0	0
Changes in assets and liabilities
Decrease (increase) in accounts receivable									5,499	(11,215)	14,220
Decrease (increase) in accrued unbilled revenues									0	0	0
Decrease in fuel oil stock									0	0	0
Increase in materials and supplies									0	0	0
Decrease in regulatory assets									0	0	0
Increase (decrease) in regulatory liabilities											0
Increase (decrease) in accounts payable									0	0	0
Change in prepaid and accrued income taxes, tax credits and revenue taxes									58	367	(331)
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									0	0	0
Changes in other assets and liabilities									(5,499)	11,215	(14,220)
Net cash provided by operating activities									(30,646)	(32,381)	(27,639)
Cash flows from investing activities
Capital expenditures									0	0	0
Advances from (to) affiliates									(9,000)	35,700	(12,000)
Other, net									18,442	4,533	1,831
Net cash used in investing activities									9,442	40,233	(10,169)
Cash flows from financing activities
Common stock dividends									30,704	32,748	27,308
Preferred stock dividends of Hawaiian Electric and subsidiaries									0	0	0
Proceeds from issuance of common stock									(18,500)	(4,900)	(1,500)
Proceeds from issuance of long-term debt									0	0	0
Repayment of long-term debt and funds transferred for repayment of long-term debt									0	0	0
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									9,000		12,000
Net increase (decrease) in other bank borrowings with original maturities of three months or less										(35,700)
Proceeds from issuance of short-term debt									0	0	0
Repayment of short-term debt									0	0
Other									0	0	0
Net cash used in financing activities									21,204	(7,852)	37,808
Net decrease in cash and equivalents									0	0	0
Cash, cash equivalents and restricted cash, January 1				$ 0				$ 0	0	0	0
Cash, cash equivalents and restricted cash, December 31	0				0				0	0	$ 0
Less: Restricted cash	0				0				0	0
Cash and cash equivalents	$ 0				$ 0				$ 0	$ 0