Retirement benefits - (Details) - HECO (USD $)	6 Months Ended				6 Months Ended			3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Apr. 02, 2011	Jun. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries	Dec. 31, 2011 Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2012 Pension benefits Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2011 Pension benefits Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2012 Pension benefits Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2011 Pension benefits Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2012 Other benefits Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2011 Other benefits Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2012 Other benefits Hawaiian Electric Company, Inc. and Subsidiaries	Jun. 30, 2011 Other benefits Hawaiian Electric Company, Inc. and Subsidiaries
Retirement benefits
Contributions made to defined benefit plans	$ 53,000,000	$ 38,000,000			$ 52,000,000	$ 37,000,000
Current estimate of contributions to defined benefit plans in current fiscal year	107,000,000		75,000,000		104,000,000		73,000,000
Benefits expected to be paid directly by the company in current fiscal year, comparable to prior year	2,000,000				800,000	1,300,000
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%
Components of net periodic benefit cost
Service cost								11,000,000	8,474,000	20,802,000	17,039,000	959,000	1,129,000	2,007,000	2,352,000
Interest cost								15,465,000	14,803,000	30,726,000	29,652,000	2,147,000	2,340,000	4,352,000	4,724,000
Expected return on plan assets								(15,942,000)	(15,352,000)	(32,002,000)	(30,636,000)	(2,519,000)	(2,618,000)	(5,098,000)	(5,226,000)
Amortization of net transition obligation												(2,000)	(2,000)	(4,000)	(4,000)
Amortization of net prior service gain								(172,000)	(187,000)	(344,000)	(374,000)	(451,000)	(312,000)	(902,000)	(539,000)
Amortization of net actuarial loss								5,845,000	4,016,000	11,714,000	8,136,000	288,000	37,000	728,000	55,000
Net periodic benefit cost								16,196,000	11,754,000	30,896,000	23,817,000	422,000	574,000	1,083,000	1,362,000
Impact of PUC D&Os								(4,977,000)	(556,000)	(8,834,000)	(2,100,000)	(416,000)	1,734,000	(1,096,000)	2,752,000
Net periodic benefit cost (adjusted for impact of PUC D&Os)								11,219,000	11,198,000	22,062,000	21,717,000	6,000	2,308,000	(13,000)	4,114,000
Retirement benefits expense					$ 15,000,000	$ 19,000,000