Electric utility segment 2014 Agreement (Details) $ in Millions	1 Months Ended	12 Months Ended
	Apr. 30, 2014 order	Dec. 31, 2012 USD ($)	Jan. 28, 2013 USD ($)
Regulatory projects and legal obligations
Remaining recoverable project costs included in rate base, in accordance with the settlement agreement		$ 52.0
Number of orders from regulatory agency | order	4
Hawaiian Electric Company, Inc. and Subsidiaries
Regulatory projects and legal obligations
Period to file required plan	120 days
Reliability standards, regulatory filing period	120 days
Period to file implementation plan	60 days
Period for full implementation of plan	180 days
Period to file action plan	30 days
Period to file implementation proposal	120 days
Regulatory response filing period	90 days
Hawaiian Electric Company, Inc. and Subsidiaries | CIS project
Regulatory projects and legal obligations
Project costs to be written off, subject to approval by PUC			$ 40.0
After-tax charge to net income due to write-off of project costs		24.0
HECO | CIS project
Regulatory projects and legal obligations
After-tax charge to net income due to write-off of project costs		17.1
HELCO | CIS project
Regulatory projects and legal obligations
After-tax charge to net income due to write-off of project costs		3.4
MECO
Regulatory projects and legal obligations
Program and system information protocol, filing period	120 days
MECO | CIS project
Regulatory projects and legal obligations
After-tax charge to net income due to write-off of project costs		$ 3.2