Retirement benefits - (Details) - HECO (USD $)	9 Months Ended				9 Months Ended			3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011	Sep. 30, 2012 Maximum	Sep. 30, 2012 Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2011 Hawaiian Electric Company, Inc. and Subsidiaries	Dec. 31, 2011 Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2012 Pension benefits Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2011 Pension benefits Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2012 Pension benefits Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2011 Pension benefits Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2012 Other benefits Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2011 Other benefits Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2012 Other benefits Hawaiian Electric Company, Inc. and Subsidiaries	Sep. 30, 2011 Other benefits Hawaiian Electric Company, Inc. and Subsidiaries
Retirement benefits
Contributions made to defined benefit plans	$ 64,000,000				$ 62,000,000	$ 55,000,000
Current estimate of contributions to defined benefit plans in current fiscal year	78,000,000		75,000,000		63,000,000		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
Funded status of retirement plan (as a percent)				80.00%
Components of net periodic benefit cost
Service cost								10,400,000	8,182,000	31,202,000	25,221,000	1,003,000	827,000	3,010,000	3,179,000
Interest cost								15,364,000	14,656,000	46,090,000	44,308,000	2,175,000	2,197,000	6,527,000	6,921,000
Expected return on plan assets								(16,001,000)	(15,574,000)	(48,003,000)	(46,210,000)	(2,548,000)	(2,655,000)	(7,646,000)	(7,881,000)
Amortization of net transition obligation												(2,000)	(2,000)	(6,000)	(6,000)
Amortization of net prior service gain								(173,000)	(187,000)	(517,000)	(561,000)	(450,000)	(590,000)	(1,352,000)	(1,129,000)
Amortization of net actuarial loss								5,857,000	3,679,000	17,571,000	11,815,000	363,000	104,000	1,091,000	159,000
Net periodic benefit cost								15,447,000	10,756,000	46,343,000	34,573,000	541,000	(119,000)	1,624,000	1,243,000
Impact of PUC D&Os								(3,460,000)	(713,000)	(12,294,000)	(2,813,000)	(552,000)	327,000	(1,648,000)	3,079,000
Net periodic benefit cost (adjusted for impact of PUC D&Os)								11,987,000	10,043,000	34,049,000	31,760,000	(11,000)	208,000	(24,000)	4,322,000
Retirement benefits expense					24,000,000	27,000,000
Utilities' expense for the defined contribution pension plan	$ 2,700,000	$ 2,600,000			$ 200,000