Electric utility segment - Condensed consolidating statement of cash flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net income	$ 46,161	$ 40,720
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment	57,435	53,091
Other amortization	9,792	8,745
Deferred income taxes	(3,171)	(2,889)
Allowance for equity funds used during construction	(2,910)	(3,294)
Other	(3,482)	2,150
Changes in assets and liabilities
Decrease (increase) in fuel oil stock	(37,574)	(1,704)
Increase in regulatory assets	(5,040)	(16,900)
Change in prepaid and accrued income taxes, tax credits and revenue taxes	(33,136)	(29,842)
Increase in defined benefit pension and other postretirement benefit plans liability	3,220	(390)
Net cash provided by operating activities	77,169	34,677
Cash flows from investing activities
Capital expenditures	(120,424)	(129,022)
Advances (to) from affiliates	3,530	2,593
Net cash used in investing activities	(82,978)	(231,051)
Cash flows from financing activities
Common stock dividends	(34,860)	(33,741)
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less	11,407	120,485
Proceeds from other bank borrowings	644,000	60,000
Other	(4,257)	(4,043)
Net cash provided by financing activities	23,008	179,278
Net increase (decrease) in cash and cash equivalents	17,199	(17,096)
Cash and cash equivalents, beginning of period	169,208	261,881
Cash and cash equivalents, end of period	186,407	244,785
Consolidating adjustments
Cash flows from operating activities
Net income	(11,849)	(9,325)
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries	11,849	9,325
Common stock dividends received from subsidiaries	(6,311)	(6,827)
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
Other	0	0
Changes in assets and liabilities
Decrease in accounts receivable	(15,083)	1,662
Decrease in accrued unbilled revenues	0	0
Decrease (increase) in fuel oil stock	0	0
Increase in materials and supplies	0	0
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	440
Increase in defined benefit pension and other postretirement benefit plans liability	0	0
Change in other assets and liabilities	15,083	(1,662)
Net cash provided by operating activities	(6,311)	(6,387)
Cash flows from investing activities
Capital expenditures	0	0
Other	18,700	(9,000)
Advances (to) from affiliates	0	(440)
Net cash used in investing activities	18,700	(9,440)
Cash flows from financing activities
Common stock dividends	6,311	6,827
Preferred stock dividends of Hawaiian Electric and subsidiaries	0	0
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less	(18,700)	9,000
Proceeds from other bank borrowings	0
Other	0	0
Net cash provided by financing activities	(12,389)	15,827
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
Hawaiian Electric (parent only) | Reportable Legal Entities
Cash flows from operating activities
Net income	32,396	27,745
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries	(11,874)	(9,350)
Common stock dividends received from subsidiaries	6,311	6,827
Depreciation of property, plant and equipment	35,867	34,439
Other amortization	5,740	3,237
Deferred income taxes	(2,757)	(271)
Allowance for equity funds used during construction	(2,447)	(2,887)
Other	(1,288)	2,868
Changes in assets and liabilities
Decrease in accounts receivable	42,419	(13,255)
Decrease in accrued unbilled revenues	18,745	6,558
Decrease (increase) in fuel oil stock	(36,828)	(1,322)
Increase in materials and supplies	(475)	(1,095)
Increase in regulatory assets	(1,114)	(13,256)
Increase (decrease) in accounts payable	6,251	(2,028)
Change in prepaid and accrued income taxes, tax credits and revenue taxes	(25,874)	(25,892)
Increase in defined benefit pension and other postretirement benefit plans liability	2,322	(592)
Change in other assets and liabilities	(9,249)	2,976
Net cash provided by operating activities	58,145	14,702
Cash flows from investing activities
Capital expenditures	(78,220)	(80,899)
Other	(9,500)	(3,000)
Advances (to) from affiliates	1,221	269
Net cash used in investing activities	(86,499)	(83,630)
Cash flows from financing activities
Common stock dividends	(25,313)	(25,826)
Preferred stock dividends of Hawaiian Electric and subsidiaries	(270)	(270)
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less	15,199	104,984
Proceeds from other bank borrowings	25,000
Other	0	(31)
Net cash provided by financing activities	14,616	78,857
Net increase (decrease) in cash and cash equivalents	(13,738)	9,929
Cash and cash equivalents, beginning of period	16,732	2,059
Cash and cash equivalents, end of period	2,994	11,988
HELCO | Reportable Legal Entities
Cash flows from operating activities
Net income	5,303	6,235
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	10,453	10,055
Other amortization	1,072	1,554
Deferred income taxes	(987)	(1,806)
Allowance for equity funds used during construction	(132)	(111)
Other	(145)	(103)
Changes in assets and liabilities
Decrease in accounts receivable	4,194	(2,048)
Decrease in accrued unbilled revenues	3,653	758
Decrease (increase) in fuel oil stock	230	(803)
Increase in materials and supplies	(883)	(550)
Increase in regulatory assets	(212)	(1,773)
Increase (decrease) in accounts payable	(4,253)	4,050
Change in prepaid and accrued income taxes, tax credits and revenue taxes	(4,078)	(1,882)
Increase in defined benefit pension and other postretirement benefit plans liability	313	(198)
Change in other assets and liabilities	(5,783)	2,875
Net cash provided by operating activities	8,745	16,253
Cash flows from investing activities
Capital expenditures	(8,371)	(14,505)
Other	(9,200)	0
Advances (to) from affiliates	(293)	264
Net cash used in investing activities	(17,864)	(14,241)
Cash flows from financing activities
Common stock dividends	(2,544)	(3,821)
Preferred stock dividends of Hawaiian Electric and subsidiaries	(134)	(134)
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less	0	3,000
Proceeds from other bank borrowings	0
Other	(1)	(2)
Net cash provided by financing activities	(2,679)	(957)
Net increase (decrease) in cash and cash equivalents	(11,798)	1,055
Cash and cash equivalents, beginning of period	15,623	4,025
Cash and cash equivalents, end of period	3,825	5,080
Maui Electric | Reportable Legal Entities
Cash flows from operating activities
Net income	6,775	3,319
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	7,627	5,972
Other amortization	(98)	553
Deferred income taxes	617	497
Allowance for equity funds used during construction	(331)	(296)
Other	(384)	(84)
Changes in assets and liabilities
Decrease in accounts receivable	5,633	(1,396)
Decrease in accrued unbilled revenues	3,435	103
Decrease (increase) in fuel oil stock	34	275
Increase in materials and supplies	(23)	350
Increase in regulatory assets	(3,714)	(1,871)
Increase (decrease) in accounts payable	(2,925)	3,121
Change in prepaid and accrued income taxes, tax credits and revenue taxes	(4,716)	(5,532)
Increase in defined benefit pension and other postretirement benefit plans liability	356	(148)
Change in other assets and liabilities	(3,449)	349
Net cash provided by operating activities	8,837	5,212
Cash flows from investing activities
Capital expenditures	(16,300)	(14,723)
Other	0	12,000
Advances (to) from affiliates	(134)	510
Net cash used in investing activities	(16,434)	(2,213)
Cash flows from financing activities
Common stock dividends	(3,767)	(3,006)
Preferred stock dividends of Hawaiian Electric and subsidiaries	(95)	(95)
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less	9,500	0
Proceeds from other bank borrowings	0
Other	(1)	0
Net cash provided by financing activities	5,637	(3,101)
Net increase (decrease) in cash and cash equivalents	(1,960)	(102)
Cash and cash equivalents, beginning of period	3,421	6,332
Cash and cash equivalents, end of period	1,461	6,230
Other subsidiaries | Reportable Legal Entities
Cash flows from operating activities
Net income	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
Other	0	0
Changes in assets and liabilities
Decrease in accounts receivable	0	0
Decrease in accrued unbilled revenues	0	0
Decrease (increase) in fuel oil stock	0	0
Increase in materials and supplies	0	0
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
Increase 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
Other	0	0
Advances (to) from affiliates	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
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less	0	0
Proceeds from other bank borrowings	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
Hawaiian Electric Company, Inc. and Subsidiaries
Cash flows from operating activities
Net income	32,625	27,974
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries	(25)	(25)
Common stock dividends received from subsidiaries	0	0
Depreciation of property, plant and equipment	53,947	50,466
Other amortization	6,714	5,344
Deferred income taxes	(3,127)	(1,580)
Allowance for equity funds used during construction	(2,910)	(3,294)
Other	(1,817)	2,681
Changes in assets and liabilities
Decrease in accounts receivable	37,163	(15,037)
Decrease in accrued unbilled revenues	25,833	7,419
Decrease (increase) in fuel oil stock	(36,564)	(1,850)
Increase in materials and supplies	(1,381)	(1,295)
Increase in regulatory assets	(5,040)	(16,900)
Increase (decrease) in accounts payable	(927)	5,143
Change in prepaid and accrued income taxes, tax credits and revenue taxes	(34,668)	(32,866)
Increase in defined benefit pension and other postretirement benefit plans liability	2,991	(938)
Change in other assets and liabilities	(3,398)	4,538
Net cash provided by operating activities	69,416	29,780
Cash flows from investing activities
Capital expenditures	(102,891)	(110,127)
Other	0	0
Advances (to) from affiliates	794	603
Net cash used in investing activities	(102,097)	(109,524)
Cash flows from financing activities
Common stock dividends	(25,313)	(25,826)
Preferred stock dividends of Hawaiian Electric and subsidiaries	(499)	(499)
Increase (decrease) in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less	5,999	116,984
Proceeds from other bank borrowings	25,000	0
Other	(2)	(33)
Net cash provided by financing activities	5,185	90,626
Net increase (decrease) in cash and cash equivalents	(27,496)	10,882
Cash and cash equivalents, beginning of period	35,877	12,517
Cash and cash equivalents, end of period	$ 8,381	$ 23,399