Electric utility segment - Consolidating Statement of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net income for common stock	$ 49,573	$ 65,900	$ 46,054	$ 40,247	$ 32,370	$ 60,073	$ 38,661	$ 34,193	$ 201,774	$ 165,297	$ 248,256
Other comprehensive income (loss), net of taxes:
Effective portion of foreign currency hedge net unrealized gains net of taxes									0	0	(281)
Reclassification adjustment to net income, net of (taxes) benefit									0	454	(119)
Net gains (losses) arising during the period, net of (taxes) benefits of $9,810, $(41,129) and $27,703 for 2018, 2017 and 2016, respectively									(28,101)	65,531	(43,510)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $7,317, $10,041 and $9,267 for 2018, 2017 and 2016, respectively									21,015	15,737	14,518
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits of $(2,887), $49,523 and $(18,206) for 2018, 2017 and 2016, respectively									8,325	(78,724)	28,584
Other comprehensive income (loss), net of taxes									(8,669)	(1,372)	(6,867)
Comprehensive income attributable to Hawaiian Electric Company, Inc.									193,105	163,925	241,389
Hawaiian Electric
Net income for common stock									143,653	119,951	142,317
Other comprehensive income (loss), net of taxes:
Effective portion of foreign currency hedge net unrealized gains net of taxes											(281)
Reclassification adjustment to net income, net of (taxes) benefit										454	(173)
Net gains (losses) arising during the period, net of (taxes) benefits of $9,810, $(41,129) and $27,703 for 2018, 2017 and 2016, respectively									(26,019)	63,105	(42,631)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $7,317, $10,041 and $9,267 for 2018, 2017 and 2016, respectively									19,012	14,477	13,254
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits of $(2,887), $49,523 and $(18,206) for 2018, 2017 and 2016, respectively									8,325	(78,724)	28,584
Other comprehensive income (loss), net of taxes									1,318	(688)	(1,247)
Comprehensive income attributable to Hawaiian Electric Company, Inc.									144,971	119,263	141,070
Hawaii Electric Light Company, Inc. (HELCO)
Net income for common stock									24,481	20,146	21,255
Other comprehensive income (loss), net of taxes:
Effective portion of foreign currency hedge net unrealized gains net of taxes											0
Reclassification adjustment to net income, net of (taxes) benefit										0	0
Net gains (losses) arising during the period, net of (taxes) benefits of $9,810, $(41,129) and $27,703 for 2018, 2017 and 2016, respectively									(6,090)	3,093	(5,141)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $7,317, $10,041 and $9,267 for 2018, 2017 and 2016, respectively									2,819	1,903	1,718
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits of $(2,887), $49,523 and $(18,206) for 2018, 2017 and 2016, respectively									3,305	(4,994)	3,269
Other comprehensive income (loss), net of taxes									34	2	(154)
Comprehensive income attributable to Hawaiian Electric Company, Inc.									24,515	20,148	21,101
Maui Electric Company, Limited (MECO)
Net income for common stock									20,912	17,911	21,136
Other comprehensive income (loss), net of taxes:
Effective portion of foreign currency hedge net unrealized gains net of taxes											0
Reclassification adjustment to net income, net of (taxes) benefit										0	0
Net gains (losses) arising during the period, net of (taxes) benefits of $9,810, $(41,129) and $27,703 for 2018, 2017 and 2016, respectively									(5,004)	7,329	(5,447)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $7,317, $10,041 and $9,267 for 2018, 2017 and 2016, respectively									2,423	1,619	1,549
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits of $(2,887), $49,523 and $(18,206) for 2018, 2017 and 2016, respectively									2,788	(9,003)	3,852
Other comprehensive income (loss), net of taxes									207	(55)	(46)
Comprehensive income attributable to Hawaiian Electric Company, Inc.									21,119	17,856	21,090
Other subsidiaries
Net income for common stock									0	0	0
Other comprehensive income (loss), net of taxes:
Effective portion of foreign currency hedge net unrealized gains net of taxes											0
Reclassification adjustment to net income, net of (taxes) benefit										0	0
Net gains (losses) arising during the period, net of (taxes) benefits of $9,810, $(41,129) and $27,703 for 2018, 2017 and 2016, respectively									0	0	0
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $7,317, $10,041 and $9,267 for 2018, 2017 and 2016, respectively									0	0	0
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits of $(2,887), $49,523 and $(18,206) for 2018, 2017 and 2016, respectively									0	0	0
Other comprehensive income (loss), net of taxes									0	0	0
Comprehensive income attributable to Hawaiian Electric Company, Inc.									0	0	0
Consolidating adjustments
Net income for common stock									(45,393)	(38,057)	(42,391)
Other comprehensive income (loss), net of taxes:
Effective portion of foreign currency hedge net unrealized gains net of taxes											0
Reclassification adjustment to net income, net of (taxes) benefit										0	0
Net gains (losses) arising during the period, net of (taxes) benefits of $9,810, $(41,129) and $27,703 for 2018, 2017 and 2016, respectively									11,094	(10,422)	10,588
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $7,317, $10,041 and $9,267 for 2018, 2017 and 2016, respectively									(5,242)	(3,522)	(3,267)
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits of $(2,887), $49,523 and $(18,206) for 2018, 2017 and 2016, respectively									(6,093)	13,997	(7,121)
Other comprehensive income (loss), net of taxes									(241)	53	200
Comprehensive income attributable to Hawaiian Electric Company, Inc.									(45,634)	(38,004)	(42,191)
HECO Consolidated
Net income for common stock	$ 35,297	$ 49,712	$ 31,169	$ 27,475	$ 25,355	$ 47,487	$ 25,644	$ 21,465	143,653	119,951	142,317
Other comprehensive income (loss), net of taxes:
Effective portion of foreign currency hedge net unrealized gains net of taxes									0	0	(281)
Reclassification adjustment to net income, net of (taxes) benefit									0	454	(173)
Net gains (losses) arising during the period, net of (taxes) benefits of $9,810, $(41,129) and $27,703 for 2018, 2017 and 2016, respectively									(26,019)	63,105	(42,631)
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $7,317, $10,041 and $9,267 for 2018, 2017 and 2016, respectively									19,012	14,477	13,254
Reclassification adjustment for impact of D&Os of the PUC included in regulatory assets, net of (taxes) benefits of $(2,887), $49,523 and $(18,206) for 2018, 2017 and 2016, respectively									8,325	(78,724)	28,584
Other comprehensive income (loss), net of taxes									1,318	(688)	(1,247)
Comprehensive income attributable to Hawaiian Electric Company, Inc.									$ 144,971	$ 119,263	$ 141,070