Cash flows (Details) - HECO (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Supplemental disclosures of cash flow information
Income taxes paid/(refunded)		$ (19)
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid	40	43
Income taxes paid/(refunded)	2	(27)
Supplemental disclosures of noncash activities
Additions to electric utility property, plant and equipment - Unpaid invoices and other	$ 27	$ 21