Electric utility segment - Condensed consolidating statement of cash flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Cash flows from operating activities
Net cash provided by operating activities	$ 312,268	$ 341,428
Cash flows from investing activities
Capital expenditures	(296,172)	(332,273)
Other	4,899	3,495
Net cash used in investing activities	(1,144,633)	(373,434)
Cash flows from financing activities
Common stock dividends	(108,066)	(104,591)
Proceeds from issuance of short-term debt	(112,710)	64,844
Proceeds from issuance of long-term debt	365,146	208,970
Repayment of short-term debt	(100,000)	0
Repayment of long-term debt and funds transferred for repayment of long-term debt	(178,291)	(204,278)
Net increase in other bank borrowings with original maturities of three months or less	6,765	19,150
Other	(7,275)	(4,266)
Net cash provided by financing activities	819,687	39,786
Net increase (decrease) in cash, cash equivalents and restricted cash	(12,678)	7,780
Cash, cash equivalents and restricted cash, beginning of period	227,685	169,208
Cash, cash equivalents and restricted cash, end of period	215,007	176,988
Less: Restricted cash	(21,881)	0	$ (30,872)
Cash and cash equivalents, end of period	193,126	176,988	196,813
Consolidating adjustments
Cash flows from operating activities
Net cash provided by operating activities	(22,624)	(18,935)
Cash flows from investing activities
Capital expenditures	0	0
Advances from (to) affiliates	(7,200)	37,200
Other	(404)	0
Net cash used in investing activities	(7,604)	37,200
Cash flows from financing activities
Common stock dividends	23,028	18,936
Preferred stock dividends of Hawaiian Electric and subsidiaries	0	0
Proceeds from issuance of short-term debt	0	0
Proceeds from issuance of long-term debt	0	0
Repayment of short-term debt	0
Repayment of long-term debt and funds transferred for repayment of long-term debt	0	0
Net increase in other bank borrowings with original maturities of three months or less	7,200	(37,200)
Other	0	(1)
Net cash provided by financing activities	30,228	(18,265)
Net increase (decrease) in cash, cash equivalents and restricted cash	0	0
Cash, cash equivalents and restricted cash, beginning of period	0	0
Cash, cash equivalents and restricted cash, end of period	0	0
Less: Restricted cash	0		0
Cash and cash equivalents, end of period	0		0
Hawaiian Electric (parent only) | Reportable Legal Entities
Cash flows from operating activities
Net cash provided by operating activities	205,645	223,733
Cash flows from investing activities
Capital expenditures	(180,088)	(223,803)
Advances from (to) affiliates	(800)	(22,200)
Other	5,636	2,975
Net cash used in investing activities	(175,252)	(243,028)
Cash flows from financing activities
Common stock dividends	(80,352)	(75,939)
Preferred stock dividends of Hawaiian Electric and subsidiaries	(810)	(810)
Proceeds from issuance of short-term debt	100,000	25,000
Proceeds from issuance of long-term debt	205,000	120,000
Repayment of short-term debt	(100,000)
Repayment of long-term debt and funds transferred for repayment of long-term debt	(95,000)	(121,546)
Net increase in other bank borrowings with original maturities of three months or less	(46,987)	77,353
Other	(1,249)	578
Net cash provided by financing activities	(19,398)	24,636
Net increase (decrease) in cash, cash equivalents and restricted cash	10,995	5,341
Cash, cash equivalents and restricted cash, beginning of period	32,988	16,732
Cash, cash equivalents and restricted cash, end of period	43,983	22,073
Less: Restricted cash	(20,458)		(30,749)
Cash and cash equivalents, end of period	23,525		2,239
HELCO
Cash flows from financing activities
Repayment of long-term debt and funds transferred for repayment of long-term debt	(14,000)
HELCO | Reportable Legal Entities
Cash flows from operating activities
Net cash provided by operating activities	27,256	41,694
Cash flows from investing activities
Capital expenditures	(48,750)	(29,119)
Advances from (to) affiliates	8,000	(15,000)
Other	1,056	(283)
Net cash used in investing activities	(39,694)	(44,402)
Cash flows from financing activities
Common stock dividends	(12,240)	(7,635)
Preferred stock dividends of Hawaiian Electric and subsidiaries	(400)	(400)
Proceeds from issuance of short-term debt	0	0
Proceeds from issuance of long-term debt	10,000	70,000
Repayment of short-term debt	0
Repayment of long-term debt and funds transferred for repayment of long-term debt		(70,000)
Net increase in other bank borrowings with original maturities of three months or less	26,500	0
Other	(67)	123
Net cash provided by financing activities	9,793	(7,912)
Net increase (decrease) in cash, cash equivalents and restricted cash	(2,645)	(10,620)
Cash, cash equivalents and restricted cash, beginning of period	7,008	15,623
Cash, cash equivalents and restricted cash, end of period	4,363	5,003
Less: Restricted cash	0		(123)
Cash and cash equivalents, end of period	4,363		6,885
Maui Electric
Cash flows from financing activities
Repayment of long-term debt and funds transferred for repayment of long-term debt	0
Maui Electric | Reportable Legal Entities
Cash flows from operating activities
Net cash provided by operating activities	34,678	36,126
Cash flows from investing activities
Capital expenditures	(38,644)	(44,885)
Advances from (to) affiliates	0	0
Other	1,031	(30)
Net cash used in investing activities	(37,613)	(44,915)
Cash flows from financing activities
Common stock dividends	(10,788)	(11,301)
Preferred stock dividends of Hawaiian Electric and subsidiaries	(286)	(286)
Proceeds from issuance of short-term debt	0	0
Proceeds from issuance of long-term debt	40,000	10,000
Repayment of short-term debt	0
Repayment of long-term debt and funds transferred for repayment of long-term debt		(10,000)
Net increase in other bank borrowings with original maturities of three months or less	(25,700)	22,200
Other	(253)	85
Net cash provided by financing activities	2,973	10,698
Net increase (decrease) in cash, cash equivalents and restricted cash	38	1,909
Cash, cash equivalents and restricted cash, beginning of period	1,797	3,421
Cash, cash equivalents and restricted cash, end of period	1,835	5,330
Less: Restricted cash	0		0
Cash and cash equivalents, end of period	1,835		1,797
Other subsidiaries
Cash flows from financing activities
Repayment of long-term debt and funds transferred for repayment of long-term debt	0
Other subsidiaries | Reportable Legal Entities
Cash flows from operating activities
Net cash provided by operating activities	0	0
Cash flows from investing activities
Capital expenditures	0	0
Advances from (to) affiliates	0	0
Other	(24)	0
Net cash used in investing activities	(24)	0
Cash flows from financing activities
Common stock dividends	0	0
Preferred stock dividends of Hawaiian Electric and subsidiaries	0	0
Proceeds from issuance of short-term debt	0	0
Proceeds from issuance of long-term debt	0	0
Repayment of short-term debt	0
Repayment of long-term debt and funds transferred for repayment of long-term debt		0
Net increase in other bank borrowings with original maturities of three months or less	0	0
Other	0	0
Net cash provided by financing activities	0	0
Net increase (decrease) in cash, cash equivalents and restricted cash	(24)	0
Cash, cash equivalents and restricted cash, beginning of period	101	101
Cash, cash equivalents and restricted cash, end of period	77	101
Less: Restricted cash	0		0
Cash and cash equivalents, end of period	77		101
Hawaiian Electric Company, Inc. and Subsidiaries
Cash flows from operating activities
Net cash provided by operating activities	244,955	282,618
Cash flows from investing activities
Capital expenditures	(267,482)	(297,807)
Advances from (to) affiliates	0	0
Other	7,295	2,662
Net cash used in investing activities	(260,187)	(295,145)
Cash flows from financing activities
Common stock dividends	(80,352)	(75,939)
Preferred stock dividends of Hawaiian Electric and subsidiaries	(1,496)	(1,496)
Proceeds from issuance of short-term debt	100,000	25,000
Proceeds from issuance of long-term debt	255,000	200,000
Repayment of short-term debt	(100,000)	0
Repayment of long-term debt and funds transferred for repayment of long-term debt	(109,000)	(201,546)
Net increase in other bank borrowings with original maturities of three months or less	(38,987)	62,353
Other	(1,569)	785
Net cash provided by financing activities	23,596	9,157
Net increase (decrease) in cash, cash equivalents and restricted cash	8,364	(3,370)
Cash, cash equivalents and restricted cash, beginning of period	41,894	35,877
Cash, cash equivalents and restricted cash, end of period	50,258	32,507
Less: Restricted cash	(20,458)	0	(30,872)
Cash and cash equivalents, end of period	$ 29,800	$ 32,507	$ 11,022