Cash flows (Details) - HECO (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011
Supplemental disclosures of cash flow information
Income taxes paid/(refunded)	$ 6	$ (21)
Hawaiian Electric Company, Inc. and Subsidiaries
Supplemental disclosures of cash flow information
Interest paid	29	29
Income taxes paid/(refunded)	3	(27)
Supplemental disclosures of noncash activities
Additions to electric utility property, plant and equipment - Unpaid invoices and other	$ 12	$ 10