Electric utility segment Related-Party Transactions (Details) - Hawaiian Electric Industries, Inc. - HECO - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Related Party Transaction [Line Items]
Amount charged to subsidiaries for general management and administrative services	$ 7.0	$ 6.2	$ 6.1
Effective interest rate basis term	30 days
Line of credit facility basis point spread (as a percent)	0.15%