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Electric utility segment - Power purchase agreements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 161	$ 153	$ 301	$ 280
Hawaiian Electric (parent only) | Kalaeloa Partners, L.P. (Kalaeloa)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	52	48	92	88
Hawaiian Electric (parent only) | AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	32	35	69	64
Hawaiian Electric (parent only) | HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	17	16	32	33
Hawaiian Electric (parent only) | Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	4	10	15	18
Hawaiian Electric (parent only) | Hamakua Energy Partners, L.P. (HEP)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	15	10	22	17
Hawaiian Electric (parent only) | Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power	$ 41	$ 34	$ 71	$ 60

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Amount of operating expense for purchased power of regulated operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(b))
-URI http://asc.fasb.org/extlink&oid=115205541&loc=SL114868664-224227

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