Electric utility segment - Unconsolidated variable interest entities (Details)	1 Months Ended	9 Months Ended
	Mar. 31, 2004 USD ($) security	Sep. 30, 2017 USD ($) agreement entity	Dec. 31, 2016 USD ($)
Hawaiian Electric Company
Power purchase agreement
Number of power purchase agreements (PPAs) (in agreements) | agreement		5
Number of entities currently required to be consolidated as VIEs (in entities) | entity		0
Number of IPPs | entity		3
Number of firm capacity producers declining to provide financial information to determine primary beneficiary status (in entities) | entity		2
Minimum potential number of IPP entities consolidated into company in the future (in entities) | entity		1
Variable Interest Entity, Not Primary Beneficiary
Unconsolidated variable interest entities
Investment in 2004 Debentures		$ 51,500,000	$ 51,500,000
Interest income		$ 2,500,000
Variable Interest Entity, Not Primary Beneficiary | Hawaiian Electric Company
Unconsolidated variable interest entities
Principal amount of 2004 Debentures	$ 31,500,000
Percent of ownership in Trust III (as a percent)		100.00%
Variable Interest Entity, Not Primary Beneficiary | Hawaiian Electric Company | 2004 Trust Preferred Securities
Unconsolidated variable interest entities
Number of 2004 Trust Preferred Securities issued (in securities) | security	2,000,000
Dividend rate on 2004 Trust Preferred Securities (as a percent)	6.50%
Aggregate Liquidation preference	$ 50,000,000
Balance of Trust Securities		$ 50,000,000	50,000,000
Dividend distributions on Trust Preferred Securities		2,400,000
Variable Interest Entity, Not Primary Beneficiary | Hawaiian Electric Company | Trust Common Securities
Unconsolidated variable interest entities
Aggregate Liquidation preference	1,500,000
Balance of Trust Securities		1,500,000	$ 1,500,000
Common dividend		$ 75,000
Variable Interest Entity, Not Primary Beneficiary | Hawaii Electric Light Company, Inc. (HELCO)
Unconsolidated variable interest entities
Principal amount of 2004 Debentures	10,000,000
Variable Interest Entity, Not Primary Beneficiary | Maui Electric
Unconsolidated variable interest entities
Principal amount of 2004 Debentures	$ 10,000,000