Long-term debt (Details) (USD $)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Long-term debt	$ 1,340,070,000	$ 1,364,942,000
Aggregate principal payments
2012	65,000,000
2013	50,000,000
2014	111,000,000
2016	75,000,000
6.50% Junior Subordinated Deferrable Interest Debentures, Series 2004, due 2034
Long-term debt
Debt instrument, stated interest rate (as a percent)	6.50%
Unsecured debt	51,546,000	51,546,000
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Obligations to the State of Hawaii	51,546,000	51,546,000
Special purpose revenue bonds issued on behalf of electric utility subsidiaries
Long-term debt
Unsecured debt	1,007,900,000	1,007,900,000
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Obligations to the State of Hawaii	1,007,900,000	1,007,900,000
Less unamortized discount	(1,376,000)	(1,504,000)
Long-term debt	1,006,524,000	1,006,396,000
4.75-4.95%, due 2012-2025
Long-term debt
Debt instrument, stated interest rate, minimum (as a percent)	4.75%
Debt instrument, stated interest rate, maximum (as a percent)	4.95%
Unsecured debt	118,500,000	118,500,000
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Obligations to the State of Hawaii	118,500,000	118,500,000
5.00-5.50%, due 2014-2032
Long-term debt
Debt instrument, stated interest rate, minimum (as a percent)	5.00%
Debt instrument, stated interest rate, maximum (as a percent)	5.50%
Unsecured debt	203,400,000	203,400,000
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Obligations to the State of Hawaii	203,400,000	203,400,000
5.65-5.75%, due 2018-2027
Long-term debt
Debt instrument, stated interest rate, minimum (as a percent)	5.65%
Debt instrument, stated interest rate, maximum (as a percent)	5.75%
Unsecured debt	216,000,000	216,000,000
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Obligations to the State of Hawaii	216,000,000	216,000,000
6.15-6.20%, due 2020-2029
Long-term debt
Debt instrument, stated interest rate, minimum (as a percent)	6.15%
Debt instrument, stated interest rate, maximum (as a percent)	6.20%
Unsecured debt	55,000,000	55,000,000
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Obligations to the State of Hawaii	55,000,000	55,000,000
4.60-4.65%, due 2026-2037
Long-term debt
Debt instrument, stated interest rate, minimum (as a percent)	4.60%
Debt instrument, stated interest rate, maximum (as a percent)	4.65%
Unsecured debt	265,000,000	265,000,000
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Obligations to the State of Hawaii	265,000,000	265,000,000
6.50%, due 2039
Long-term debt
Debt instrument, stated interest rate (as a percent)	6.50%
Unsecured debt	150,000,000	150,000,000
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Obligations to the State of Hawaii	150,000,000	150,000,000
HEI medium-term notes 4.23-6.141%, due 2011
Long-term debt
Debt instrument, stated interest rate, minimum (as a percent)	4.23%
Debt instrument, stated interest rate, maximum (as a percent)	6.141%
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Long-term debt		150,000,000
HEI medium-term note 7.13%, due 2012
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Long-term debt	7,000,000	7,000,000
HEI medium-term note 5.25%, due 2013
Long-term debt
Debt instrument, stated interest rate (as a percent)	5.25%
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Long-term debt	50,000,000	50,000,000
HEI medium-term note 6.51%, due 2014
Long-term debt
Debt instrument, stated interest rate (as a percent)	6.51%
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Long-term debt	100,000,000	100,000,000
HEI senior note 4.41%, due 2016
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Long-term debt	75,000,000
HEI senior note 5.67%, due 2021
Obligations to the State of Hawaii for the repayment of special purpose revenue bonds issued on behalf of electric utility subsidiaries
Long-term debt	$ 50,000,000

Interest rate stated in the contractual debt agreement.

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