Retirement benefits - (Details) - HECO (Hawaiian Electric Company, Inc. and Subsidiaries, USD $)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended				12 Months Ended
	Jun. 30, 2011 Pension benefits	Jun. 30, 2010 Pension benefits	Jun. 30, 2011 Pension benefits	Jun. 30, 2010 Pension benefits	Jun. 30, 2011 Other benefits	Jun. 30, 2010 Other benefits	Jun. 30, 2011 Other benefits	Jun. 30, 2010 Other benefits	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Retirement benefits
Contributions made to defined benefit plans									$ 37,000,000	$ 16,000,000	$ 31,000,000
Current estimate of contributions to defined benefit plans in current fiscal year									73,000,000
Percentage of target liability funded (as a percent)											96.00%
Percentage of increase in target liability funded in current and future years (as a percent)									100.00%
Benefits expected to be paid directly by the company in current fiscal year, comparable to prior year									1,000,000
Components of net periodic benefit cost
Service cost	8,474,000	6,772,000	17,039,000	13,382,000	1,129,000	1,131,000	2,352,000	2,219,000
Interest cost	14,803,000	14,658,000	29,652,000	29,237,000	2,340,000	2,571,000	4,724,000	5,167,000
Expected return on plan assets	(15,352,000)	(15,353,000)	(30,636,000)	(30,677,000)	(2,618,000)	(2,728,000)	(5,226,000)	(5,443,000)
Amortization of unrecognized transition obligations					(2,000)	(2,000)	(4,000)	(4,000)
Amortization of prior service gain	(187,000)	(187,000)	(374,000)	(374,000)	(312,000)	(56,000)	(539,000)	(111,000)
Recognized actuarial loss	4,016,000	1,767,000	8,136,000	3,452,000	37,000	1,000	55,000	4,000
Net periodic benefit cost	11,754,000	7,657,000	23,817,000	15,020,000	574,000	917,000	1,362,000	1,832,000
Impact of PUC DandOs	(556,000)	2,020,000	(2,100,000)	5,028,000	1,734,000	1,333,000	2,752,000	2,621,000
Net periodic benefit cost (adjusted for impact of PUC DandOs)	11,198,000	9,677,000	21,717,000	20,048,000	2,308,000	2,250,000	4,114,000	4,453,000
Retirement benefits expense									$ 19,000,000	$ 19,000,000