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Other related-party transactions (Details) - Affiliated Entity - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Hawaii Medical Service Association (HMSA) | Gross costs
Related Party Transaction [Line Items]
Expenses from related party transactions	$ 28	$ 28	$ 30
Hawaii Medical Service Association (HMSA) | Gross costs | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from related party transactions	23	22	23
Hawaii Medical Service Association (HMSA) | Net expense
Related Party Transaction [Line Items]
Expenses from related party transactions	19	20	21
Hawaii Medical Service Association (HMSA) | Net expense | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from related party transactions	14	14	14
Hawaii Dental Service (HDS) | Gross costs
Related Party Transaction [Line Items]
Expenses from related party transactions	3	3	3
Hawaii Dental Service (HDS) | Gross costs | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from related party transactions	2	2	2
Hawaii Dental Service (HDS) | Net expense
Related Party Transaction [Line Items]
Expenses from related party transactions	2	2	2
Hawaii Dental Service (HDS) | Net expense | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from related party transactions	$ 1	$ 1	$ 1

X

- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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