Electric utility segment - Consolidating Statement of Cash Flows (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities
Net income (loss)	$ 66,736,000	$ 63,890,000	$ 42,985,000	$ 46,161,000	$ 50,046,000	$ 66,371,000	$ 46,527,000	$ 40,720,000	$ 219,772,000	$ 203,664,000	$ 167,187,000
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation of property, plant and equipment									229,858,000	214,036,000	200,658,000
Other amortization									48,255,000	41,593,000	21,340,000
Deferred income taxes									(15,085,000)	(9,368,000)	37,835,000
Allowance for equity funds used during construction									(11,987,000)	(10,877,000)	(12,483,000)
Other									10,822,000	(4,219,000)	(3,324,000)
Changes in assets and liabilities
Decrease (increase) in fuel oil stock									(11,493,000)	7,054,000	(20,794,000)
Decrease (increase) in regulatory assets									71,262,000	9,252,000	(17,256,000)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(27,538,000)	29,429,000	20,685,000
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(4,482,000)	20,871,000	882,000
Net cash provided by operating activities									512,470,000	499,312,000	420,441,000
Cash flows from investing activities
Capital expenditures									(457,520,000)	(537,369,000)	(495,187,000)
Other, net									13,292,000	14,534,000	7,487,000
Net cash used in investing activities									(541,709,000)	(792,059,000)	(815,299,000)
Cash flows from financing activities
Common stock dividends									(139,463,000)	(134,987,000)	(134,873,000)
Proceeds from issuance of long-term debt									289,349,000	250,000,000	532,325,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									(287,285,000)	(53,887,000)	(465,000,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									86,718,000	(18,999,000)	67,992,000
Proceeds from issuance of short-term debt									75,000,000	25,000,000	125,000,000
Net increase in other bank borrowings with original maturities of three months or less									5,070,000	71,556,000	61,776,000
Repayment of short-term debt									(50,000,000)	(50,000,000)	(75,000,000)
Other									(1,836,000)	(1,603,000)	(6,349,000)
Net cash used in financing activities									87,716,000	200,074,000	378,287,000
Net decrease in cash and equivalents									58,477,000	(92,673,000)	(16,571,000)
Cash, cash equivalents and restricted cash, January 1				169,208,000				261,881,000	169,208,000	261,881,000	278,452,000
Cash, cash equivalents and restricted cash, December 31	227,685,000				169,208,000				227,685,000	169,208,000	261,881,000
Less: Restricted cash	(30,872,000)				0				(30,872,000)	0	0
Cash and cash equivalents	196,813,000				169,208,000				196,813,000	169,208,000	261,881,000
Parent Company
Cash flows from operating activities
Net income (loss)									217,882,000	201,774,000	165,297,000
Adjustments to reconcile net income to net cash provided by operating activities
Depreciation of property, plant and equipment									570,000	597,000	548,000
Changes in assets and liabilities
Net cash provided by operating activities									131,120,000	135,470,000	99,600,000
Cash flows from investing activities
Capital expenditures									(47,000)	(143,000)	(317,000)
Other, net									(1,001,000)	140,000	(177,000)
Net cash used in investing activities									(41,170,000)	(92,569,000)	(26,456,000)
Cash flows from financing activities
Common stock dividends									(139,463,000)	(134,987,000)	(134,873,000)
Proceeds from issuance of long-term debt									0	150,000,000	150,000,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									0	0	(200,000,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									47,731,000	(14,000,000)	62,993,000
Proceeds from issuance of short-term debt									0	0	125,000,000
Repayment of short-term debt									0	(50,000,000)	(75,000,000)
Other									(10,000)	(848,000)	(756,000)
Net cash used in financing activities									(92,739,000)	(50,861,000)	(76,366,000)
Net decrease in cash and equivalents									(2,789,000)	(7,960,000)	(3,222,000)
Cash, cash equivalents and restricted cash, January 1				3,742,000				11,702,000	3,742,000	11,702,000	14,924,000
Cash, cash equivalents and restricted cash, December 31	953,000				3,742,000				953,000	3,742,000	11,702,000
Hawaiian Electric Company, Inc. and Subsidiaries
Cash flows from operating activities
Net income (loss)	45,860,000	$ 47,277,000	$ 33,073,000	32,625,000	35,796,000	$ 50,210,000	$ 31,668,000	27,974,000	158,835,000	145,648,000	121,946,000
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									(37,000)	(100,000)	(100,000)
Common stock dividends received from subsidiaries									35,000	100,000	125,000
Depreciation of property, plant and equipment									215,731,000	203,626,000	192,784,000
Other amortization									29,631,000	26,602,000	8,498,000
Deferred income taxes									(16,284,000)	(7,982,000)	38,037,000
Income tax credits, net									27,259,000	(99,000)	(52,000)
State refundable credit									(8,369,000)	(6,239,000)	(2,251,000)
Allowance for equity funds used during construction									(11,987,000)	(10,877,000)	(12,483,000)
Other									200,000	4,768,000	1,237,000
Changes in assets and liabilities
Decrease (increase) in accounts receivable									20,956,000	(50,917,000)	2,914,000
Decrease (increase) in accrued unbilled revenues									4,511,000	(14,684,000)	(15,361,000)
Decrease (increase) in fuel oil stock									(12,002,000)	6,938,000	(20,443,000)
Decrease (increase) in materials and supplies									(5,498,000)	(807,000)	(718,000)
Decrease (increase) in regulatory assets									71,262,000	9,252,000	(17,256,000)
Increase in regulatory liabilities									1,953,000	37,358,000	3,602,000
Increase (decrease) in accounts payable									(2,051,000)	24,358,000	25,734,000
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(28,523,000)	25,036,000	29,862,000
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(4,448,000)	18,746,000	604,000
Changes in other assets and liabilities									(17,218,000)	(17,114,000)	(21,493,000)
Net cash provided by operating activities									423,956,000	393,613,000	335,186,000
Cash flows from investing activities
Capital expenditures									(419,898,000)	(415,264,000)	(376,865,000)
Advances from (to) affiliates									0	0	0
Other, net									11,374,000	10,082,000	4,578,000
Net cash used in investing activities									(408,524,000)	(405,182,000)	(372,287,000)
Cash flows from financing activities
Common stock dividends									(101,252,000)	(103,305,000)	(87,767,000)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(1,995,000)	(1,995,000)	(1,995,000)
Net proceeds from issuance of common stock									35,500,000	70,700,000	14,000,000
Proceeds from issuance of long-term debt									280,000,000	100,000,000	315,000,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									(283,546,000)	(50,000,000)	(265,000,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									38,987,000	(4,999,000)	4,999,000
Proceeds from issuance of short-term debt										25,000,000
Net increase in other bank borrowings with original maturities of three months or less									75,000,000
Repayment of short-term debt									(50,000,000)	0	0
Other									(2,109,000)	(472,000)	(3,905,000)
Net cash used in financing activities									(9,415,000)	34,929,000	(24,668,000)
Net decrease in cash and equivalents									6,017,000	23,360,000	(61,769,000)
Cash, cash equivalents and restricted cash, January 1				35,877,000				12,517,000	35,877,000	12,517,000	74,286,000
Cash, cash equivalents and restricted cash, December 31	41,894,000				35,877,000				41,894,000	35,877,000	12,517,000
Less: Restricted cash	(30,872,000)				0				(30,872,000)	0	0
Cash and cash equivalents	11,022,000				35,877,000				11,022,000	35,877,000	12,517,000
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Parent Company
Cash flows from operating activities
Net income (loss)									157,920,000	144,733,000	121,031,000
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									(43,204,000)	(45,493,000)	(38,157,000)
Common stock dividends received from subsidiaries									32,783,000	27,408,000	36,867,000
Depreciation of property, plant and equipment									143,470,000	137,410,000	130,889,000
Other amortization									23,351,000	20,956,000	2,398,000
Deferred income taxes									(13,547,000)	(9,806,000)	26,342,000
Income tax credits, net									27,277,000	(83,000)	(35,000)
State refundable credit									(6,245,000)	(4,941,000)	(1,382,000)
Allowance for equity funds used during construction									(9,955,000)	(9,208,000)	(10,896,000)
Other									298,000	3,991,000	263,000
Changes in assets and liabilities
Decrease (increase) in accounts receivable									25,376,000	(51,656,000)	1,817,000
Decrease (increase) in accrued unbilled revenues									4,912,000	(10,884,000)	(11,355,000)
Decrease (increase) in fuel oil stock									(14,741,000)	10,710,000	(17,733,000)
Decrease (increase) in materials and supplies									(4,585,000)	(1,966,000)	1,603,000
Decrease (increase) in regulatory assets									55,494,000	12,192,000	(8,395,000)
Increase in regulatory liabilities									102,000	26,540,000	2,552,000
Increase (decrease) in accounts payable									4,687,000	14,748,000	23,519,000
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(24,900,000)	24,438,000	16,716,000
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(3,033,000)	17,178,000	709,000
Changes in other assets and liabilities									(15,341,000)	(8,056,000)	(18,765,000)
Net cash provided by operating activities									340,119,000	298,211,000	257,988,000
Cash flows from investing activities
Capital expenditures									(311,538,000)	(305,703,000)	(281,752,000)
Advances from (to) affiliates									(27,700,000)	0	0
Other, net									5,241,000	3,226,000	(1,711,000)
Net cash used in investing activities									(333,997,000)	(302,477,000)	(283,463,000)
Cash flows from financing activities
Common stock dividends									(101,252,000)	(103,305,000)	(87,767,000)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(1,080,000)	(1,080,000)	(1,080,000)
Net proceeds from issuance of common stock									35,500,000	70,700,000	14,000,000
Proceeds from issuance of long-term debt									190,000,000	75,000,000	202,000,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									(183,546,000)	(30,000,000)	(162,000,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									46,987,000	(16,999,000)	3,499,000
Proceeds from issuance of short-term debt										25,000,000
Net increase in other bank borrowings with original maturities of three months or less									75,000,000
Repayment of short-term debt									(50,000,000)
Other									(1,475,000)	(377,000)	(2,506,000)
Net cash used in financing activities									10,134,000	18,939,000	(33,854,000)
Net decrease in cash and equivalents									16,256,000	14,673,000	(59,329,000)
Cash, cash equivalents and restricted cash, January 1				16,732,000				2,059,000	16,732,000	2,059,000	61,388,000
Cash, cash equivalents and restricted cash, December 31	32,988,000				16,732,000				32,988,000	16,732,000	2,059,000
Less: Restricted cash	(30,749,000)								(30,749,000)
Cash and cash equivalents	2,239,000				16,732,000				2,239,000	16,732,000
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Hawaii Electric Light
Cash flows from operating activities
Net income (loss)									21,351,000	25,015,000	20,680,000
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									41,812,000	40,235,000	38,741,000
Other amortization									4,810,000	5,069,000	3,225,000
Deferred income taxes									(2,383,000)	(341,000)	3,954,000
Income tax credits, net									(13,000)	(14,000)	(16,000)
State refundable credit									(559,000)	(547,000)	(528,000)
Allowance for equity funds used during construction									(816,000)	(478,000)	(554,000)
Other									(48,000)	348,000	974,000
Changes in assets and liabilities
Decrease (increase) in accounts receivable									3,326,000	(4,867,000)	(359,000)
Decrease (increase) in accrued unbilled revenues									(20,000)	(1,111,000)	(2,376,000)
Decrease (increase) in fuel oil stock									2,126,000	(2,329,000)	(469,000)
Decrease (increase) in materials and supplies									(1,158,000)	886,000	(661,000)
Decrease (increase) in regulatory assets									9,218,000	71,000	(4,007,000)
Increase in regulatory liabilities									(1,558,000)	5,380,000	315,000
Increase (decrease) in accounts payable									(3,160,000)	6,104,000	(3,547,000)
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(893,000)	(2,118,000)	7,961,000
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(762,000)	(760,000)	52,000
Changes in other assets and liabilities									(6,152,000)	2,806,000	(748,000)
Net cash provided by operating activities									65,121,000	73,349,000	62,637,000
Cash flows from investing activities
Capital expenditures									(49,811,000)	(51,054,000)	(47,784,000)
Advances from (to) affiliates									(8,000,000)	0	3,500,000
Other, net									297,000	1,182,000	649,000
Net cash used in investing activities									(57,514,000)	(49,872,000)	(43,635,000)
Cash flows from financing activities
Common stock dividends									(17,680,000)	(15,289,000)	(24,796,000)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(534,000)	(534,000)	(534,000)
Net proceeds from issuance of common stock									0	0
Proceeds from issuance of long-term debt									72,500,000	15,000,000	28,000,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									(70,000,000)	(11,000,000)	(28,000,000)
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 issuance of short-term debt										0
Net increase in other bank borrowings with original maturities of three months or less									0
Repayment of short-term debt									0
Other									(508,000)	(56,000)	(396,000)
Net cash used in financing activities									(16,222,000)	(11,879,000)	(25,726,000)
Net decrease in cash and equivalents									(8,615,000)	11,598,000	(6,724,000)
Cash, cash equivalents and restricted cash, January 1				15,623,000				4,025,000	15,623,000	4,025,000	10,749,000
Cash, cash equivalents and restricted cash, December 31	7,008,000				15,623,000				7,008,000	15,623,000	4,025,000
Less: Restricted cash	(123,000)								(123,000)
Cash and cash equivalents	6,885,000				15,623,000				6,885,000	15,623,000
Hawaiian Electric Company, Inc. and Subsidiaries | Reportable Legal Entities | Maui Electric
Cash flows from operating activities
Net income (loss)									22,731,000	21,293,000	18,292,000
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									30,449,000	25,981,000	23,154,000
Other amortization									1,470,000	577,000	2,875,000
Deferred income taxes									(354,000)	2,165,000	8,004,000
Income tax credits, net									(5,000)	(2,000)	(1,000)
State refundable credit									(1,565,000)	(751,000)	(341,000)
Allowance for equity funds used during construction									(1,216,000)	(1,191,000)	(1,033,000)
Other									(50,000)	429,000	0
Changes in assets and liabilities
Decrease (increase) in accounts receivable									3,469,000	(8,614,000)	45,000
Decrease (increase) in accrued unbilled revenues									(381,000)	(2,689,000)	(1,630,000)
Decrease (increase) in fuel oil stock									613,000	(1,443,000)	(2,241,000)
Decrease (increase) in materials and supplies									245,000	273,000	(1,660,000)
Decrease (increase) in regulatory assets									6,550,000	(3,011,000)	(4,854,000)
Increase in regulatory liabilities									3,409,000	5,438,000	735,000
Increase (decrease) in accounts payable									(3,578,000)	3,506,000	5,762,000
Change in prepaid and accrued income taxes, tax credits and revenue taxes									(3,097,000)	3,047,000	5,362,000
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									(653,000)	2,328,000	(157,000)
Changes in other assets and liabilities									(6,940,000)	2,356,000	(569,000)
Net cash provided by operating activities									51,097,000	49,692,000	51,743,000
Cash flows from investing activities
Capital expenditures									(58,549,000)	(58,507,000)	(47,329,000)
Advances from (to) affiliates									0	12,000,000	(2,000,000)
Other, net									1,303,000	3,843,000	400,000
Net cash used in investing activities									(57,246,000)	(42,664,000)	(48,929,000)
Cash flows from financing activities
Common stock dividends									(15,068,000)	(12,019,000)	(11,946,000)
Preferred stock dividends of Hawaiian Electric and subsidiaries									(381,000)	(381,000)	(381,000)
Net proceeds from issuance of common stock									4,900,000	1,500,000	4,800,000
Proceeds from issuance of long-term debt									17,500,000	10,000,000	85,000,000
Repayment of long-term debt and funds transferred for repayment of long-term debt									(30,000,000)	(9,000,000)	(75,000,000)
Net increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less									27,700,000	0	0
Proceeds from issuance of short-term debt										0
Net increase in other bank borrowings with original maturities of three months or less									0
Repayment of short-term debt									0
Other									(126,000)	(39,000)	(1,003,000)
Net cash used in financing activities									4,525,000	(9,939,000)	1,470,000
Net decrease in cash and equivalents									(1,624,000)	(2,911,000)	4,284,000
Cash, cash equivalents and restricted cash, January 1				3,421,000				6,332,000	3,421,000	6,332,000	2,048,000
Cash, cash equivalents and restricted cash, December 31	1,797,000				3,421,000				1,797,000	3,421,000	6,332,000
Less: Restricted cash	0								0
Cash and cash equivalents	1,797,000				3,421,000				1,797,000	3,421,000
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									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
Income tax credits, net									0	0	0
State refundable credit									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
Decrease (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 in regulatory liabilities										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 (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									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 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	0
Proceeds from issuance of short-term debt										0
Net increase in other bank borrowings with original maturities of three months or less									0
Repayment of short-term debt									0
Other									0	0	0
Net cash used in financing activities									0	0	0
Net decrease in cash and equivalents									0	0	0
Cash, cash equivalents and restricted cash, January 1				101,000				101,000	101,000	101,000	101,000
Cash, cash equivalents and restricted cash, December 31	101,000				101,000				101,000	101,000	101,000
Less: Restricted cash	0								0
Cash and cash equivalents	101,000				101,000				101,000	101,000
Hawaiian Electric Company, Inc. and Subsidiaries | Consolidating Adjustments
Cash flows from operating activities
Net income (loss)									(43,167,000)	(45,393,000)	(38,057,000)
Adjustments to reconcile net income to net cash provided by operating activities
Equity in earnings									43,167,000	45,393,000	38,057,000
Common stock dividends received from subsidiaries									(32,748,000)	(27,308,000)	(36,742,000)
Depreciation of property, plant and equipment									0	0	0
Other amortization									0	0	0
Deferred income taxes									0	0	(263,000)
Income tax credits, net									0	0	0
State refundable credit									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									(11,215,000)	14,220,000	1,411,000
Decrease (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 in regulatory liabilities										0	0
Increase (decrease) in accounts payable									0	0	0
Change in prepaid and accrued income taxes, tax credits and revenue taxes									367,000	(331,000)	(177,000)
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability									0	0	0
Changes in other assets and liabilities									11,215,000	(14,220,000)	(1,411,000)
Net cash provided by operating activities									(32,381,000)	(27,639,000)	(37,182,000)
Cash flows from investing activities
Capital expenditures									0	0	0
Advances from (to) affiliates									35,700,000	(12,000,000)	(1,500,000)
Other, net									4,533,000	1,831,000	5,240,000
Net cash used in investing activities									40,233,000	(10,169,000)	3,740,000
Cash flows from financing activities
Common stock dividends									32,748,000	27,308,000	36,742,000
Preferred stock dividends of Hawaiian Electric and subsidiaries									0	0	0
Net proceeds from issuance of common stock									(4,900,000)	(1,500,000)	(4,800,000)
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									(35,700,000)	12,000,000	1,500,000
Proceeds from issuance of short-term debt										0
Net increase in other bank borrowings with original maturities of three months or less									0
Repayment of short-term debt									0
Other									0	0	0
Net cash used in financing activities									(7,852,000)	37,808,000	33,442,000
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
Cash and cash equivalents	$ 0				$ 0				$ 0	$ 0