Electric utility segment - Condensed consolidating statement of cash flows (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net income	$ 66,371	$ 60,544	$ 153,618	$ 134,344
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property, plant and equipment			159,646	150,123
Other amortization			31,473	15,362
Deferred income taxes			10,823	21,397
Allowance for equity funds used during construction	(1,962)	(3,482)	(8,239)	(8,908)
Other			(4,524)	(1,350)
Changes in assets and liabilities
Decrease (increase) in fuel oil stock			(5,060)	6,177
Increase in regulatory assets			(6,474)	3,922
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(32,006)	2,828
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability			7,517	670
Net cash provided by operating activities			257,679	320,114
Cash flows from investing activities
Capital expenditures			(404,984)	(343,375)
Contributions in aid of construction			24,361	40,603
Other			13,669	1,345
Net cash used in investing activities			(541,761)	(469,330)
Cash flows from financing activities
Common stock dividends			(101,235)	(101,149)
Proceeds from issuance of long-term debt			100,000	265,000
Funds transferred for redemption of special purpose revenue bonds			(1,867)	(265,000)
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			85,369	24,498
Other			(5,668)	(9,531)
Net cash provided by financing activities			194,255	72,937
Net decrease in cash and cash equivalents			(89,827)	(76,279)
Cash and cash equivalents, beginning of period			261,881	278,452
Cash and cash equivalents, end of period	172,054	202,173	172,054	202,173
Consolidating adjustments
Cash flows from operating activities
Net income	(16,636)	(12,767)	(35,041)	(29,306)
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries			35,041	29,306
Common stock dividends received from subsidiaries			(20,481)	(20,581)
Depreciation of property, plant and equipment			0	0
Other amortization			0	0
Deferred income taxes			0	4,641
Allowance for equity funds used during construction	0	0	0	0
Other			0	0
Changes in assets and liabilities
Increase in accounts receivable			1,664	1,066
Decrease (increase) in accrued unbilled revenues			0	0
Decrease (increase) in fuel oil stock			0	0
Decrease (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			(331)	(5,081)
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability			0	0
Change in other assets and liabilities			(1,664)	(1,066)
Net cash provided by operating activities			(20,812)	(21,021)
Cash flows from investing activities
Capital expenditures			0	0
Contributions in aid of construction			0	0
Other			331	440
Advances (to) from affiliates			(10,000)	(2,900)
Net cash used in investing activities			(9,669)	(2,460)
Cash flows from financing activities
Common stock dividends			20,481	20,581
Preferred stock dividends of Hawaiian Electric and subsidiaries			0	0
Proceeds from issuance of long-term debt			0
Proceeds from issuance of special purpose revenue bonds
Funds transferred for redemption of special purpose revenue bonds				0
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			10,000	2,900
Other			0	0
Net cash provided by financing activities			30,481	23,481
Net 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	49,982	47,757	109,166	95,406
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries			(35,116)	(29,381)
Common stock dividends received from subsidiaries			20,531	20,656
Depreciation of property, plant and equipment			103,112	98,167
Other amortization			15,159	2,168
Deferred income taxes			7,182	12,166
Allowance for equity funds used during construction	(1,648)	(3,108)	(7,123)	(7,823)
Other			(1,227)	216
Changes in assets and liabilities
Increase in accounts receivable			(41,566)	(6,114)
Decrease (increase) in accrued unbilled revenues			(17,780)	(14,823)
Decrease (increase) in fuel oil stock			3,862	6,779
Decrease (increase) in materials and supplies			(4,082)	1,063
Increase in regulatory assets			(1,704)	9,471
Increase (decrease) in accounts payable			(10,541)	7,010
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(20,949)	10,920
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability			6,018	532
Change in other assets and liabilities			34,934	(2,709)
Net cash provided by operating activities			159,876	203,704
Cash flows from investing activities
Capital expenditures			(245,393)	(236,727)
Contributions in aid of construction			19,486	34,787
Other			4,518	6,089
Advances (to) from affiliates			(2,000)	0
Net cash used in investing activities			(223,389)	(195,851)
Cash flows from financing activities
Common stock dividends			(77,479)	(65,825)
Preferred stock dividends of Hawaiian Electric and subsidiaries			(810)	(810)
Proceeds from issuance of long-term debt			75,000
Proceeds from issuance of special purpose revenue bonds				162,000
Funds transferred for redemption of special purpose revenue bonds				(162,000)
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			68,914	3,100
Other			(304)	(2,252)
Net cash provided by financing activities			65,321	(65,787)
Net decrease in cash and cash equivalents			1,808	(57,934)
Cash and cash equivalents, beginning of period			2,059	61,388
Cash and cash equivalents, end of period	3,867	3,454	3,867	3,454
HELCO | Reportable Legal Entities
Cash flows from operating activities
Net income	9,308	6,567	19,439	15,050
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			30,165	29,056
Other amortization			3,992	1,718
Deferred income taxes			1,195	5,237
Allowance for equity funds used during construction	(39)	(167)	(274)	(416)
Other			(315)	566
Changes in assets and liabilities
Increase in accounts receivable			(6,738)	(1,127)
Decrease (increase) in accrued unbilled revenues			130	(1,581)
Decrease (increase) in fuel oil stock			(2,785)	195
Decrease (increase) in materials and supplies			201	(1,580)
Increase in regulatory assets			(2,245)	(2,935)
Increase (decrease) in accounts payable			234	(2,660)
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(9,828)	(758)
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability			(570)	39
Change in other assets and liabilities			2,602	1,059
Net cash provided by operating activities			35,203	41,863
Cash flows from investing activities
Capital expenditures			(43,417)	(36,700)
Contributions in aid of construction			2,960	3,460
Other			1,177	871
Advances (to) from affiliates			0	(3,100)
Net cash used in investing activities			(39,280)	(35,469)
Cash flows from financing activities
Common stock dividends			(11,467)	(11,622)
Preferred stock dividends of Hawaiian Electric and subsidiaries			(400)	(400)
Proceeds from issuance of long-term debt			15,000
Proceeds from issuance of special purpose revenue bonds				28,000
Funds transferred for redemption of special purpose revenue bonds				(28,000)
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			0	0
Other			(54)	(407)
Net cash provided by financing activities			3,079	(12,429)
Net decrease in cash and cash equivalents			(998)	(6,035)
Cash and cash equivalents, beginning of period			4,025	10,749
Cash and cash equivalents, end of period	3,027	4,714	3,027	4,714
Maui Electric | Reportable Legal Entities
Cash flows from operating activities
Net income	7,556	6,428	16,288	14,942
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			18,533	17,355
Other amortization			672	2,232
Deferred income taxes			4,458	7,493
Allowance for equity funds used during construction	(275)	(207)	(842)	(669)
Other			(410)	(256)
Changes in assets and liabilities
Increase in accounts receivable			(6,499)	(1,912)
Decrease (increase) in accrued unbilled revenues			(2,998)	(1,610)
Decrease (increase) in fuel oil stock			(6,026)	(797)
Decrease (increase) in materials and supplies			(229)	(1,763)
Increase in regulatory assets			(2,525)	(2,614)
Increase (decrease) in accounts payable			1,595	1,780
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(6,029)	210
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability			440	(118)
Change in other assets and liabilities			3,027	54
Net cash provided by operating activities			19,455	34,327
Cash flows from investing activities
Capital expenditures			(45,920)	(33,548)
Contributions in aid of construction			1,915	2,356
Other			3,785	714
Advances (to) from affiliates			12,000	6,000
Net cash used in investing activities			(28,220)	(24,478)
Cash flows from financing activities
Common stock dividends			(9,014)	(8,959)
Preferred stock dividends of Hawaiian Electric and subsidiaries			(286)	(286)
Proceeds from issuance of long-term debt			10,000
Proceeds from issuance of special purpose revenue bonds				75,000
Funds transferred for redemption of special purpose revenue bonds				(75,000)
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			2,000	0
Other			(38)	(934)
Net cash provided by financing activities			2,662	(10,179)
Net decrease in cash and cash equivalents			(6,103)	(330)
Cash and cash equivalents, beginning of period			6,332	2,048
Cash and cash equivalents, end of period	229	1,718	229	1,718
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
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
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 (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
Contributions in aid of construction			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
Proceeds from issuance of long-term debt			0
Proceeds from issuance of special purpose revenue bonds				0
Funds transferred for redemption of special purpose revenue bonds				0
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			0	0
Other			0	0
Net cash provided by financing activities			0	0
Net 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	50,210	47,985	109,852	96,092
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of subsidiaries			(75)	(75)
Common stock dividends received from subsidiaries			50	75
Depreciation of property, plant and equipment			151,810	144,578
Other amortization			19,823	6,118
Deferred income taxes			12,835	29,537
Allowance for equity funds used during construction	(1,962)	(3,482)	(8,239)	(8,908)
Other			(1,952)	526
Changes in assets and liabilities
Increase in accounts receivable			(53,139)	(8,087)
Decrease (increase) in accrued unbilled revenues			(20,648)	(18,014)
Decrease (increase) in fuel oil stock			(4,949)	6,177
Decrease (increase) in materials and supplies			(4,110)	(2,280)
Increase in regulatory assets			(6,474)	3,922
Increase (decrease) in accounts payable			(8,712)	6,130
Change in prepaid and accrued income taxes, tax credits and revenue taxes			(37,137)	5,291
Increase (decrease) in defined benefit pension and other postretirement benefit plans liability			5,888	453
Change in other assets and liabilities			38,899	(2,662)
Net cash provided by operating activities			193,722	258,873
Cash flows from investing activities
Capital expenditures			(334,730)	(306,975)
Contributions in aid of construction			24,361	40,603
Other			9,811	8,114
Advances (to) from affiliates			0	0
Net cash used in investing activities			(300,558)	(258,258)
Cash flows from financing activities
Common stock dividends			(77,479)	(65,825)
Preferred stock dividends of Hawaiian Electric and subsidiaries			(1,496)	(1,496)
Proceeds from issuance of long-term debt			100,000	265,000
Proceeds from issuance of special purpose revenue bonds				265,000
Funds transferred for redemption of special purpose revenue bonds			0	(265,000)
Net increase in short-term borrowings from non-affiliates and affiliate with original maturities of three months or less			80,914	6,000
Other			(396)	(3,593)
Net cash provided by financing activities			101,543	(64,914)
Net decrease in cash and cash equivalents			(5,293)	(64,299)
Cash and cash equivalents, beginning of period			12,517	74,286
Cash and cash equivalents, end of period	$ 7,224	$ 9,987	$ 7,224	$ 9,987