Electric utility segment - Condensed consolidating statement of cash flows (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net income	$ 42,985	$ 46,527	$ 89,146	$ 87,247
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment			114,863	106,063
Other amortization			22,439	20,603
Deferred income taxes			(6,662)	(9,672)
Allowance for equity funds used during construction	(3,175)	(2,983)	(6,085)	(6,277)
Other			(7,320)	(147)
Changes in assets and liabilities
Decrease (increase) in fuel oil stock			(40,557)	(19,867)
Decrease (increase) in regulatory assets			25,392	(19,600)
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(45,977)	(26,558)
Decrease in defined benefit pension and other postretirement benefit plans liability			(1,774)	(871)
Net cash provided by operating activities			133,406	108,271
Cash flows from investing activities
Capital expenditures			(229,282)	(246,325)
Other			6,143	13,657
Net cash used in investing activities			(275,130)	(391,420)
Cash flows from financing activities
Common stock dividends			(69,720)	(67,481)
Proceeds from issuance of long-term debt			56,150	100,000
Repayment of long-term debt			(52,489)	(878)
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			112,901	84,881
Net increase in other bank borrowings with original maturities of three months or less			1,445	38,446
Other			1,189	(230)
Net cash provided by financing activities			171,065	275,933
Net increase (decrease) in cash and cash equivalents			29,341	(7,216)
Cash and cash equivalents, beginning of period			169,208	261,881
Cash and cash equivalents, end of period	198,549	254,665	198,549	254,665
Consolidating adjustments
Cash flows from operating activities
Net income	(8,086)	(9,080)	(19,935)	(18,405)
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries			19,935	18,405
Common stock dividends received from subsidiaries			(12,624)	(13,654)
Depreciation of property, plant and equipment			0	0
Other amortization			0	0
Deferred income taxes			0	0
Allowance for equity funds used during construction	0	0	0	0
Other			0	0
Changes in assets and liabilities
Decrease (increase) in accounts receivable			(2,341)	(245)
Decrease (increase) in accrued unbilled revenues			0	0
Decrease (increase) in fuel oil stock			0	0
Decrease (increase) in materials and supplies			0	0
Decrease (increase) in regulatory assets			0	0
Increase (decrease) in accounts payable			0	0
Change in prepaid and accrued income taxes, tax credits and revenue taxes			0	(601)
Decrease in defined benefit pension and other postretirement benefit plans liability			0	0
Change in other assets and liabilities			2,341	245
Net cash provided by operating activities			(12,624)	(14,255)
Cash flows from investing activities
Capital expenditures			0	0
Advances to affiliates			30,300	(5,400)
Other			0	601
Net cash used in investing activities			30,300	(4,799)
Cash flows from financing activities
Common stock dividends			12,624	13,654
Preferred stock dividends of Hawaiian Electric and subsidiaries			0	0
Proceeds from issuance of long-term debt			0	0
Repayment of long-term debt			0
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			0	5,400
Net increase in other bank borrowings with original maturities of three months or less			(30,300)
Other			0	0
Net cash provided by financing activities			(17,676)	19,054
Net increase (decrease) in cash and cash equivalents			0	0
Cash and cash equivalents, beginning of period			0	0
Cash and cash equivalents, end of period	0	0	0	0
Hawaiian Electric (parent only) | Reportable Legal Entities
Cash flows from operating activities
Net income	32,844	31,439	65,240	59,184
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries			(19,972)	(18,455)
Common stock dividends received from subsidiaries			12,661	13,679
Depreciation of property, plant and equipment			71,735	68,830
Other amortization			11,444	9,200
Deferred income taxes			(5,354)	(6,708)
Allowance for equity funds used during construction	(2,614)	(2,588)	(5,061)	(5,475)
Other			(2,494)	1,469
Changes in assets and liabilities
Decrease (increase) in accounts receivable			19,969	(25,673)
Decrease (increase) in accrued unbilled revenues			1,769	(3,063)
Decrease (increase) in fuel oil stock			(46,641)	(9,513)
Decrease (increase) in materials and supplies			(3,583)	(2,752)
Decrease (increase) in regulatory assets			24,318	(14,728)
Increase (decrease) in accounts payable			5,804	13,093
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(34,328)	(15,343)
Decrease in defined benefit pension and other postretirement benefit plans liability			(1,205)	(1,117)
Change in other assets and liabilities			(9,875)	1,116
Net cash provided by operating activities			84,427	63,744
Cash flows from investing activities
Capital expenditures			(150,945)	(146,920)
Advances to affiliates			(25,300)	(5,600)
Other			2,821	2,241
Net cash used in investing activities			(173,424)	(150,279)
Cash flows from financing activities
Common stock dividends			(50,626)	(51,652)
Preferred stock dividends of Hawaiian Electric and subsidiaries			(540)	(540)
Proceeds from issuance of long-term debt			30,000	75,000
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			25,000	75,881
Net increase in other bank borrowings with original maturities of three months or less			116,901
Other			197	(291)
Net cash provided by financing activities			89,386	98,398
Net increase (decrease) in cash and cash equivalents			389	11,863
Cash and cash equivalents, beginning of period			16,732	2,059
Cash and cash equivalents, end of period	17,121	13,922	17,121	13,922
HELCO
Cash flows from financing activities
Repayment of long-term debt			(10,000)
HELCO | Reportable Legal Entities
Cash flows from operating activities
Net income	4,799	3,896	10,102	10,131
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries			0	0
Common stock dividends received from subsidiaries			0	0
Depreciation of property, plant and equipment			20,906	20,093
Other amortization			2,142	2,976
Deferred income taxes			(1,554)	(2,429)
Allowance for equity funds used during construction	(218)	(124)	(350)	(235)
Other			(292)	(322)
Changes in assets and liabilities
Decrease (increase) in accounts receivable			(6,446)	(2,387)
Decrease (increase) in accrued unbilled revenues			1,622	697
Decrease (increase) in fuel oil stock			(349)	(3,934)
Decrease (increase) in materials and supplies			(2,456)	(559)
Decrease (increase) in regulatory assets			2,288	(1,974)
Increase (decrease) in accounts payable			(3,454)	3,096
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(5,111)	(9,952)
Decrease in defined benefit pension and other postretirement benefit plans liability			(377)	(380)
Change in other assets and liabilities			(265)	3,173
Net cash provided by operating activities			16,406	17,994
Cash flows from investing activities
Capital expenditures			(18,083)	(24,424)
Advances to affiliates			(5,000)	(1,000)
Other			(280)	884
Net cash used in investing activities			(23,363)	(24,540)
Cash flows from financing activities
Common stock dividends			(5,090)	(7,644)
Preferred stock dividends of Hawaiian Electric and subsidiaries			(267)	(267)
Proceeds from issuance of long-term debt			10,000	15,000
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			0	0
Net increase in other bank borrowings with original maturities of three months or less			0
Other			43	(52)
Net cash provided by financing activities			(5,314)	7,037
Net increase (decrease) in cash and cash equivalents			(12,271)	491
Cash and cash equivalents, beginning of period			15,623	4,025
Cash and cash equivalents, end of period	3,352	4,516	3,352	4,516
Maui Electric
Cash flows from financing activities
Repayment of long-term debt			(10,000)
Maui Electric | Reportable Legal Entities
Cash flows from operating activities
Net income	3,516	5,413	10,291	8,732
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries			0	0
Common stock dividends received from subsidiaries			0	0
Depreciation of property, plant and equipment			15,219	11,904
Other amortization			75	845
Deferred income taxes			297	794
Allowance for equity funds used during construction	(343)	(271)	(674)	(567)
Other			(767)	(169)
Changes in assets and liabilities
Decrease (increase) in accounts receivable			(1,188)	(5,763)
Decrease (increase) in accrued unbilled revenues			(801)	(1,419)
Decrease (increase) in fuel oil stock			5,284	(6,696)
Decrease (increase) in materials and supplies			149	(233)
Decrease (increase) in regulatory assets			(1,214)	(2,898)
Increase (decrease) in accounts payable			(2,395)	2,095
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(6,346)	(5,165)
Decrease in defined benefit pension and other postretirement benefit plans liability			(317)	(464)
Change in other assets and liabilities			(5,006)	1,357
Net cash provided by operating activities			12,607	2,353
Cash flows from investing activities
Capital expenditures			(30,868)	(28,303)
Advances to affiliates			0	12,000
Other			(31)	575
Net cash used in investing activities			(30,899)	(15,728)
Cash flows from financing activities
Common stock dividends			(7,534)	(6,010)
Preferred stock dividends of Hawaiian Electric and subsidiaries			(191)	(191)
Proceeds from issuance of long-term debt			10,000	10,000
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			0	5,600
Net increase in other bank borrowings with original maturities of three months or less			25,300
Other			83	(35)
Net cash provided by financing activities			17,658	9,364
Net increase (decrease) in cash and cash equivalents			(634)	(4,011)
Cash and cash equivalents, beginning of period			3,421	6,332
Cash and cash equivalents, end of period	2,787	2,321	2,787	2,321
Other subsidiaries
Cash flows from financing activities
Repayment of long-term debt			0
Other subsidiaries | Reportable Legal Entities
Cash flows from operating activities
Net income	0	0	0	0
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries			0	0
Common stock dividends received from subsidiaries			0	0
Depreciation of property, plant and equipment			0	0
Other amortization			0	0
Deferred income taxes			0	0
Allowance for equity funds used during construction	0	0	0	0
Other			0	0
Changes in assets and liabilities
Decrease (increase) in accounts receivable			0	0
Decrease (increase) in accrued unbilled revenues			0	0
Decrease (increase) in fuel oil stock			0	0
Decrease (increase) in materials and supplies			0	0
Decrease (increase) in regulatory assets			0	0
Increase (decrease) in accounts payable			0	0
Change in prepaid and accrued income taxes, tax credits and revenue taxes			0	0
Decrease in defined benefit pension and other postretirement benefit plans liability			0	0
Change in other assets and liabilities			0	0
Net cash provided by operating activities			0	0
Cash flows from investing activities
Capital expenditures			0	0
Advances to affiliates			0	0
Other			0	0
Net cash used in investing activities			0	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 long-term debt			0	0
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			0	0
Net increase in other bank borrowings with original maturities of three months or less			0
Other			0	0
Net cash provided by financing activities			0	0
Net increase (decrease) in cash and cash equivalents			0	0
Cash and cash equivalents, beginning of period			101	101
Cash and cash equivalents, end of period	101	101	101	101
Hawaiian Electric Company, Inc. and Subsidiaries
Cash flows from operating activities
Net income	33,073	31,668	65,698	59,642
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries			(37)	(50)
Common stock dividends received from subsidiaries			37	25
Depreciation of property, plant and equipment			107,860	100,827
Other amortization			13,661	13,021
Deferred income taxes			(6,611)	(8,343)
Allowance for equity funds used during construction	(3,175)	(2,983)	(6,085)	(6,277)
Other			(3,553)	978
Changes in assets and liabilities
Decrease (increase) in accounts receivable			9,994	(34,068)
Decrease (increase) in accrued unbilled revenues			2,590	(3,785)
Decrease (increase) in fuel oil stock			(41,706)	(20,143)
Decrease (increase) in materials and supplies			(5,890)	(3,544)
Decrease (increase) in regulatory assets			25,392	(19,600)
Increase (decrease) in accounts payable			(45)	18,284
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(45,785)	(31,061)
Decrease in defined benefit pension and other postretirement benefit plans liability			(1,899)	(1,961)
Change in other assets and liabilities			(12,805)	5,891
Net cash provided by operating activities			100,816	69,836
Cash flows from investing activities
Capital expenditures			(199,896)	(199,647)
Advances to affiliates			0	0
Other			2,510	4,301
Net cash used in investing activities			(197,386)	(195,346)
Cash flows from financing activities
Common stock dividends			(50,626)	(51,652)
Preferred stock dividends of Hawaiian Electric and subsidiaries			(998)	(998)
Proceeds from issuance of long-term debt			50,000	100,000
Repayment of long-term debt			(51,546)	0
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			25,000	86,881
Net increase in other bank borrowings with original maturities of three months or less			111,901	86,881
Other			323	(378)
Net cash provided by financing activities			84,054	133,853
Net increase (decrease) in cash and cash equivalents			(12,516)	8,343
Cash and cash equivalents, beginning of period			35,877	12,517
Cash and cash equivalents, end of period	$ 23,361	$ 20,860	23,361	$ 20,860
Hawaiian Electric Company
Cash flows from financing activities
Repayment of long-term debt			$ (31,546)