Electric utility segment (Details 6) (USD $) In Millions, unless otherwise specified		3 Months Ended	12 Months Ended		12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012 Hawaiian Electric Company, Inc. and Subsidiaries	Dec. 31, 2012 Hawaiian Electric Company, Inc. and Subsidiaries CIS project	Jan. 28, 2013 Hawaiian Electric Company, Inc. and Subsidiaries CIS project	Dec. 31, 2012 HECO CIS project	Dec. 31, 2012 HELCO CIS project	Dec. 31, 2012 MECO CIS project
Regulatory projects and legal obligations
Project costs to be written off, subject to approval by PUC				$ 40
After-tax charge to net income due to write-off of project costs		24.0	24.0		17.1	3.4	3.2
Remaining recoverable project costs included in rate base, in accordance with the settlement agreement	$ 52