Proposed merger (Details)		1 Months Ended
	Dec. 03, 2014 USD ($) $ / shares shares	Jan. 31, 2015 USD ($)	Dec. 31, 2014 complaint
Business Acquisition [Line Items]
Number of purported class action complaints filed | complaint			8
NextEra Energy, Inc Merger
Business Acquisition [Line Items]
Merger share conversion ratio | shares	0.2413
Minimum percentage of shares from which holders approval needed for merger	75.00%
Merger agreement contract extension	6 months
Merger contract termination fee	$ 90,000,000
Maximum expenses paid to party for cancellation of merger	$ 5,000,000
Subsequent event | NextEra Energy, Inc Merger
Business Acquisition [Line Items]
Minimum period that entity agrees not to submit applications for general base rate increase		4 years
Approximate amount of cumulative savings for customers due to forgone recoveries		$ 60,000,000
Hawaiian Electric Company, Inc. and Subsidiaries | NextEra Energy, Inc Merger
Business Acquisition [Line Items]
Special dividend | $ / shares	$ 0.50