Retirement benefits (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Defined contribution plan
Defined contribution plan, expenses recognized	$ 3,000,000	$ 4,000,000	$ 3,000,000
Cash contributions by the employer to defined contribution plan	4,000,000	4,000,000	4,000,000
Hawaiian Electric Company, Inc. and Subsidiaries
Defined contribution plan
Employer's additional matching contribution on the first 6 percent of employee deferrals (as a percent)	50.00%
Maximum percentage of participant deferrals eligible for Employer contribution match, towards defined contribution plan (as a percent)	6.00%
Hawaiian Electric Industries, Inc. | Hawaiian Electric Company, Inc. and Subsidiaries
Defined contribution plan
Employer's additional matching contribution on the first 6 percent of employee deferrals (as a percent)	50.00%
Maximum percentage of participant deferrals eligible for Employer contribution match, towards defined contribution plan (as a percent)	6.00%
Pension benefits
Defined benefit plans
Service cost	35,016,000	28,801,000	25,688,000
Interest cost	64,966,000	64,527,000	61,988,000
Expected return on plan assets	(68,901,000)	(68,959,000)	(57,244,000)
Amortization of net transition obligations	2,000	2,000	2,000
Amortization of net prior service (gain)	(389,000)	(388,000)	(387,000)
Amortization of net actuarial loss (gain)	16,987,000	7,392,000	15,847,000
Net periodic benefit cost	47,681,000	31,375,000	45,894,000
Impact of PUC DandOs	(3,516,000)	10,207,000	(10,570,000)
Net periodic benefit cost (adjusted for impact of PUC DandOs)	44,165,000	41,582,000	35,324,000
Amounts amortized from AOCI or regulatory assets into net periodic pension benefit cost during 2012
Prior service credit	(300,000)
Net actuarial loss	25,700,000
Pension expense	32,000,000	32,000,000	27,000,000
Other benefits
Defined benefit plans
Service cost	4,409,000	4,739,000	4,846,000
Interest cost	9,534,000	10,378,000	10,981,000
Expected return on plan assets	(10,650,000)	(11,101,000)	(8,902,000)
Amortization of net transition obligations			1,831,000
Amortization of net prior service (gain)	(1,494,000)	(396,000)	(79,000)
Amortization of net actuarial loss (gain)	234,000	(14,000)	401,000
Net periodic benefit cost	2,033,000	3,606,000	9,078,000
Impact of PUC DandOs	2,674,000	5,400,000	(132,000)
Net periodic benefit cost (adjusted for impact of PUC DandOs)	4,707,000	9,006,000	8,946,000
Amounts amortized from AOCI or regulatory assets into net periodic pension benefit cost during 2012
Prior service credit	(1,800,000)
Net actuarial loss	1,800,000
Postretirement benefits other than pension expense	4,000,000	7,000,000	7,000,000
Effect of one-percentage-point increase in assumed health care cost trend rates that would have increased total service and interest cost	200,000
Effect of one-percentage-point increase in assumed health care cost trend rates that would have increased the accumulated postretirement benefit obligation (APBO)	4,000,000
Effect of one-percentage-point decrease that would have reduced total service and interest cost	200,000
Effect of one-percentage-point decrease that would have reduced APBO	$ 5,000,000