Unconsolidated variable interest entities (Details) (USD $)	12 Months Ended												3 Months Ended	12 Months Ended
	Dec. 31, 2011 entity	Dec. 31, 2011 Electric utility mW agreement kW	Dec. 31, 2010 Electric utility	Dec. 31, 2009 Electric utility	Dec. 31, 2011 Electric utility AES Hawaii, Inc. (AES Hawaii)	Dec. 31, 2011 Electric utility Kalaeloa Partners, L.P. (Kalaeloa) mW Y	Dec. 31, 2011 Electric utility Hamakua Energy Partners, L.P. (HEP)	Dec. 31, 2011 Electric utility HPOWER	Dec. 31, 2011 Hawaiian Electric Company, Inc. (HECO) entity	Dec. 31, 2011 Hawaii Electric Light Company, Inc. (HELCO) and Maui Electric Company, Limited (MECO) entity	Dec. 31, 2011 HECO Capital Trust III	Mar. 31, 2004 HECO Capital Trust III Electric utility	Mar. 31, 2004 HECO Capital Trust III Electric utility 2004 Trust Preferred Securities security	Dec. 31, 2011 HECO Capital Trust III Electric utility 2004 Trust Preferred Securities	Dec. 31, 2011 HECO Capital Trust III Electric utility Trust Common Securities	Mar. 31, 2004 HECO Capital Trust III Electric utility Trust Common Securities	Mar. 31, 2004 HECO Capital Trust III Hawaii Electric Light Company, Inc. (HELCO)	Mar. 31, 2004 HECO Capital Trust III Maui Electric Company, Limited (MECO)
Unconsolidated variable interest entities
Number of 2004 Trust Preferred Securities issued													2,000,000
Dividend rate on 2004 Trust Preferred Securities (as a percent)													6.50%
Aggregate Liquidation preference													$ 50,000,000			$ 1,500,000
Principal amount of 2004 Debentures												31,500,000					10,000,000	10,000,000
Investment in 2004 Debentures											51,500,000
Balance of Trust Securities														50,000,000	1,500,000
Interest income											3,400,000
Dividend distributions on Trust Preferred Securities											3,300,000
Common dividend														100,000
Power purchase agreement
Number of power purchase agreements (PPAs)		6
Power purchase capacity excluding agreements with smaller IPPs (in megawatts)		548
Maximum capacity of small power production facilities (in kilowatts)		100
Percentage of power purchase from AES Hawaii, Inc. (AES Hawaii), Kalaeloa Partners, L.P. (Kalaeloa), Hamakua Energy Partners, L.P. (HEP) and HPOWER		90.00%
Purchases from IPPs	$ 690,000,000	$ 689,652,000	$ 548,800,000	$ 499,804,000	$ 133,000,000	$ 310,000,000	$ 59,000,000	$ 62,000,000
Number of largest IPP's declining to provide financial information to determine primary beneficiary status	3
Number of entities owning wind farms not required to be consolidated as VIE's										2
Minimum potential number of IPP entities consolidated into company in the future									1
Power purchase capacity (in megawatts)						180
Number of years entity entered under power purchase agreement						25
Power purchase capacity that Increases from initial capacity (in megawatts)						208