Retirement benefits - (Details) - HECO (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Apr. 02, 2011
Retirement benefits
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, comparable to prior 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%
Hawaiian Electric Company, Inc. and Subsidiaries
Retirement benefits
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, comparable to prior year	800,000		1,300,000
Components of net periodic benefit cost
Retirement benefits expense	8,000,000	9,000,000
Pension benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Components of net periodic benefit cost
Service cost	9,802,000	8,565,000
Interest cost	15,261,000	14,849,000
Expected return on plan assets	(16,060,000)	(15,284,000)
Amortization of net prior service gain	(172,000)	(187,000)
Amortization of net actuarial loss	5,869,000	4,120,000
Net periodic benefit cost	14,700,000	12,063,000
Impact of PUC D and Os	(3,857,000)	(1,544,000)
Net periodic benefit cost (adjusted for impact of PUC D and Os)	10,843,000	10,519,000
Other benefits | Hawaiian Electric Company, Inc. and Subsidiaries
Components of net periodic benefit cost
Service cost	1,048,000	1,223,000
Interest cost	2,205,000	2,384,000
Expected return on plan assets	(2,579,000)	(2,608,000)
Amortization of net transition obligation	(2,000)	(2,000)
Amortization of net prior service gain	(451,000)	(227,000)
Amortization of net actuarial loss	440,000	18,000
Net periodic benefit cost	661,000	788,000
Impact of PUC D and Os	(680,000)	1,018,000
Net periodic benefit cost (adjusted for impact of PUC D and Os)	$ (19,000)	$ 1,806,000