Retirement benefits (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Apr. 02, 2011
Defined benefit plans
Contributions made to defined benefit plans	$ 27,000,000	$ 31,000,000	$ 75,000,000
Current estimate of contributions to defined benefit plans in current fiscal year	107,000,000
Benefits expected to be paid directly by the company in current fiscal year	2,000,000
Amount available as single sum distribution option under accelerated distribution options				50,000
Funded status of retirement plan (as a percent)				80.00%
Percentage of participant's total benefit that may be elected while partial restrictions are in effect				50.00%
Defined contribution plan, expenses recognized	900,000	900,000
Cash contributions by the employer to defined contribution plan	2,200,000	2,400,000
Hawaiian Electric Industries, Inc.
Defined benefit plans
Contributions made to defined benefit plans	1,000,000		2,000,000
Current estimate of contributions to defined benefit plans in current fiscal year	2,000,000
Benefits expected to be paid directly by the company in current fiscal year	1,000,000
Retirement benefits expense	8,000,000	10,000,000
Electric utility
Defined benefit plans
Contributions made to defined benefit plans	26,000,000	31,000,000	73,000,000
Current estimate of contributions to defined benefit plans in current fiscal year	105,000,000
Benefits expected to be paid directly by the company in current fiscal year	800,000
Pension benefits | Hawaiian Electric Industries, Inc.
Defined benefit plans
Service cost	10,191,000	8,917,000
Interest cost	16,771,000	16,309,000
Expected return on plan assets	(17,856,000)	(17,101,000)
Amortization of net transition obligation		1,000
Amortization of prior service gain	(81,000)	(97,000)
Amortization of net actuarial loss	6,423,000	4,405,000
Net periodic benefit cost	15,448,000	12,434,000
Impact of PUC D and Os	(3,857,000)	(1,544,000)
Net periodic benefit cost (adjusted for impact of PUC D and Os)	11,591,000	10,890,000
Other benefits | Hawaiian Electric Industries, Inc.
Defined benefit plans
Service cost	1,096,000	1,267,000
Interest cost	2,281,000	2,461,000
Expected return on plan assets	(2,621,000)	(2,648,000)
Amortization of prior service gain	(448,000)	(224,000)
Amortization of net actuarial loss	453,000	15,000
Net periodic benefit cost	761,000	871,000
Impact of PUC D and Os	(680,000)	1,018,000
Net periodic benefit cost (adjusted for impact of PUC D and Os)	$ 81,000	$ 1,889,000