Bank segment (HEI only) - Statements 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
Condensed Statement of Income Captions [Line Items]
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
Net unrealized losses on available-for sale investment securities:
Net unrealized losses on available-for sale investment securities arising during the period, net of tax benefits of $3,468, $2,886 and $3,763 for 2018, 2017 and 2016, respectively									(9,472)	(4,370)	(5,699)
Reclassification adjustment for net realized gains included in net income, net of taxes of nil, nil and $238 for 2018, 2017 and 2016, respectively									0	0	(360)
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $1,108, $812 and $566 for 2018, 2017 and 2016, respectively									21,015	15,737	14,518
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
American Savings Bank (ASB)
Condensed Statement of Income Captions [Line Items]
Net income for common stock									82,509	66,997	57,279
Net unrealized losses on available-for sale investment securities:
Net unrealized losses on available-for sale investment securities arising during the period, net of tax benefits of $3,468, $2,886 and $3,763 for 2018, 2017 and 2016, respectively									(9,472)	(4,370)	(5,699)
Reclassification adjustment for net realized gains included in net income, net of taxes of nil, nil and $238 for 2018, 2017 and 2016, respectively									0	0	(360)
Retirement benefit plans:
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $1,108, $812 and $566 for 2018, 2017 and 2016, respectively									2,353	1,231	857
Other comprehensive income (loss), net of taxes									(7,119)	(3,139)	(5,202)
Comprehensive income attributable to Hawaiian Electric Company, Inc.									$ 75,390	$ 63,858	$ 52,077