Electric utility segment - Unconsolidated variable interest entities (Details) - Hawaiian Electric Company	9 Months Ended
	Sep. 30, 2018 agreement entity
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)	0
Number of IPPs	3
Number of firm capacity producers declining to provide financial information to determine primary beneficiary status (in entities)	2
Minimum potential number of IPP entities consolidated into company in the future (in entities)	1