Major customers (Details) - HECO (Operating revenues, Customer concentration, Various federal government agencies, USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Major customers
Operating revenues percentage	11.00%	11.00%	10.00%
Operating revenues amount	$ 349	$ 316	$ 242
Hawaiian Electric Company, Inc. and Subsidiaries
Major customers
Operating revenues percentage	11.00%	11.00%	10.00%
Operating revenues amount	$ 349	$ 316	$ 242

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

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-Section 50

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-Subparagraph (a)

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

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-Section 50

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

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-URI http://asc.fasb.org/extlink&oid=7491637&loc=d3e13531-108611

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