Bank segment (HEI only) - Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Statement of Income Captions [Line Items]
Net income for common stock	$ 32,370	$ 60,073	$ 38,661	$ 34,193	$ 44,634	$ 127,142	$ 44,128	$ 32,352	$ 165,297	$ 248,256	$ 159,877
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 $2,886, $3,763 and $1,541 for 2017, 2016 and 2015, respectively									(4,370)	(5,699)	(2,334)
Reclassification adjustment for net realized gains included in net income, net of taxes of nil, $238 and nil for 2017, 2016 and 2015, respectively									0	(360)	0
Retirement benefit plans:
Net gains arising during the period, net of taxes of nil, nil and $59 for 2017, 2016 and 2015, respectively									65,531	(43,510)	5,889
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $812, $566 and $1,011 for 2017, 2016 and 2015, respectively									15,737	14,518	22,465
Other comprehensive income (loss), net of taxes									(1,372)	(6,867)	1,116
Comprehensive income attributable to Hawaiian Electric Company, Inc.									163,925	241,389	160,993
American Savings Bank (ASB)
Condensed Statement of Income Captions [Line Items]
Net income for common stock									66,997	57,279	54,730
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 $2,886, $3,763 and $1,541 for 2017, 2016 and 2015, respectively									(4,370)	(5,699)	(2,334)
Reclassification adjustment for net realized gains included in net income, net of taxes of nil, $238 and nil for 2017, 2016 and 2015, respectively									0	(360)	0
Retirement benefit plans:
Net gains arising during the period, net of taxes of nil, nil and $59 for 2017, 2016 and 2015, respectively									0	0	90
Adjustment for amortization of prior service credit and net losses recognized during the period in net periodic benefit cost, net of tax benefits of $812, $566 and $1,011 for 2017, 2016 and 2015, respectively									1,231	857	1,531
Other comprehensive income (loss), net of taxes									(3,139)	(5,202)	(713)
Comprehensive income attributable to Hawaiian Electric Company, Inc.									$ 63,858	$ 52,077	$ 54,017