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Electric utility segment - Power purchase agreements (Details) $ in Millions	1 Months Ended				3 Months Ended		12 Months Ended
	Jul. 31, 2018 MW	Jun. 30, 2015 MW	May 31, 2012 MW	Mar. 31, 1988 MW	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 1988 MW
Hu Honua Bioenergy, LLC
Regulatory Projects and Legal Obligations [Line Items]
Minimum power volume required (in megawatts) | MW			21.5
Molokai New Energy Partners
Regulatory Projects and Legal Obligations [Line Items]
Total contracted PV capacity (in megawatts) | MW	4.88
Total contracted battery energy storage system capacity | MW	3
Maximum power volume to be delivered (in megawatts) | MW	2.64
AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchase commitment, period (in years)				30 years
Minimum power volume required (in megawatts) | MW				180
Additional capacity requirement (in megawatts) | MW		9
Hawaiian Electric (parent only)
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					$ 142	$ 140
Hawaiian Electric (parent only) | Kalaeloa
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					37	38
Increased power purchase commitment capacity (in megawatts) | MW							208
Hawaiian Electric (parent only) | AES Hawaii
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					30	31
Hawaiian Electric (parent only) | HPOWER
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					17	17
Hawaiian Electric (parent only) | Hamakua Energy
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					11	13
Hawaiian Electric (parent only) | Puna Geothermal Venture
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					4	0
Hawaiian Electric (parent only) | Wind IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					29	28
Hawaiian Electric (parent only) | Solar IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					12	11
Hawaiian Electric (parent only) | Other IPPs
Regulatory Projects and Legal Obligations [Line Items]
Purchased power					$ 2	$ 2

X

- Definition

Aggregate of Power Purchase Capacity Increases from Initial Capacity

+ References

No definition available.

+ Details

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- Definition

Long-term Contract For Purchase Of Electric Power, Maximum Power Volume Delivered

+ References

No definition available.

+ Details

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X

- Definition

Long-term Contract For Purchase Of Electric Power, Total Contracted Battery Energy Storage System Capacity

+ References

No definition available.

+ Details

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- Definition

Long-term Contract For Purchase Of Electric Power, Total Contracted PV Capacity

+ References

No definition available.

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- Definition

Long Term Purchase Commitment, Arbitration, Additional Capacity Requirement

+ References

No definition available.

+ Details

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- Definition

Long-term Purchase Commitment, Minimum Power Volume Required

+ References

No definition available.

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- Definition

Period covered by the long-term purchase commitment, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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X

- Definition

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=120395209&loc=SL114868664-224227

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