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Retirement benefits - (Details) - HECO (Hawaiian Electric Company, Inc. and Subsidiaries, USD $)	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended				12 Months Ended
	Sep. 30, 2011 Pension benefits	Sep. 30, 2010 Pension benefits	Sep. 30, 2011 Pension benefits	Sep. 30, 2010 Pension benefits	Sep. 30, 2011 Other benefits	Sep. 30, 2010 Other benefits	Sep. 30, 2011 Other benefits	Sep. 30, 2010 Other benefits	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Retirement benefits
Contributions made to defined benefit plans									$ 55,000,000	$ 24,000,000
Current estimate of contributions to defined benefit plans in current fiscal year									73,000,000		31,000,000
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	8,182,000	7,097,000	25,221,000	20,479,000	827,000	1,206,000	3,179,000	3,425,000
Interest cost	14,656,000	14,816,000	44,308,000	44,053,000	2,197,000	2,500,000	6,921,000	7,667,000
Expected return on plan assets	(15,574,000)	(15,408,000)	(46,210,000)	(46,085,000)	(2,655,000)	(2,759,000)	(7,881,000)	(8,202,000)
Amortization of unrecognized transition obligations					(2,000)	(2,000)	(6,000)	(6,000)
Amortization of prior service gain	(187,000)	(186,000)	(561,000)	(560,000)	(590,000)	(86,000)	(1,129,000)	(197,000)
Recognized actuarial loss	3,679,000	1,925,000	11,815,000	5,377,000	104,000	(2,000)	159,000	2,000
Net periodic benefit cost	10,756,000	8,244,000	34,573,000	23,264,000	(119,000)	857,000	1,243,000	2,689,000
Impact of PUC DandOs	(713,000)	2,574,000	(2,813,000)	7,602,000	327,000	1,512,000	3,079,000	4,133,000
Net periodic benefit cost (adjusted for impact of PUC DandOs)	10,043,000	10,818,000	31,760,000	30,866,000	208,000	2,369,000	4,322,000	6,822,000
Retirement benefits expense									$ 27,000,000	$ 29,000,000