Electric utility segment - Unconsolidated Variable Interest Entities (Details)	1 Months Ended	12 Months Ended
	Mar. 31, 2004 USD ($) security	Dec. 31, 2018 USD ($) agreement entity
Variable Interest Entity [Line Items]
Investment in 2004 Debentures		$ 51,500,000
Interest income		$ 3,400,000
Number of power purchase agreements (PPAs) | agreement		4
Hawaii Electric Light Company, Inc. (HELCO)
Variable Interest Entity [Line Items]
Principal amount of 2004 Debentures	$ 10,000,000
Hawaiian Electric Company, Inc (HECO)
Variable Interest Entity [Line Items]
Principal amount of 2004 Debentures	$ 31,500,000.0
Number of power purchase agreements (PPAs) | agreement		4
Number of entities owning wind farms not required to be consolidated as VIE's | entity		2
Minimum potential number of IPP entities consolidated into company in the future | entity		1
2004 Trust Preferred Securities | Hawaiian Electric
Variable Interest Entity [Line Items]
Balance of Trust Securities		$ 50,000,000
Dividend distributions on Trust Preferred Securities		3,300,000
2004 Trust Preferred Securities | Hawaiian Electric Company, Inc (HECO)
Variable Interest Entity [Line Items]
Number of 2004 Trust Preferred Securities issued | security	2,000,000
Dividend rate on 2004 Trust Preferred Securities	6.50%
Aggregate Liquidation preference	$ 50,000,000
Trust Common Securities | Hawaiian Electric
Variable Interest Entity [Line Items]
Balance of Trust Securities		1,500,000
Common dividend		$ 100,000
Trust Common Securities | Hawaiian Electric Company, Inc (HECO)
Variable Interest Entity [Line Items]
Aggregate Liquidation preference	$ 1,500,000.0