XML 86 R52.htm IDEA: XBRL DOCUMENT v3.8.0.1

Summary of significant accounting policies - Depreciation (Details) - MW		12 Months Ended
	Nov. 24, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Depreciation
Composite annual depreciation rate		3.20%	3.20%	3.20%
Minimum
Depreciation
Estimated useful life under production plant (in years)		20 years
Estimated useful life under transmission and distribution plant (in years)		25 years
Estimated useful life under general plant (in years)		5 years
Maximum
Depreciation
Estimated useful life under production plant (in years)		88 years
Estimated useful life under transmission and distribution plant (in years)		65 years
Estimated useful life under general plant (in years)		65 years
Hamakua Energy Partners, L.P. (HEP)
Depreciation
Power produced by power plants (in megawatts)	60	60

X

- Definition

Public Utilities, Power Produced By Power Plant

+ References

No definition available.

+ Details

Name:	he_PublicUtilitiesPowerProducedByPowerPlant
Namespace Prefix:	he_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Useful life of assets common to business units owned by public utility, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesPropertyPlantAndEquipmentCommonUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Composite depreciation rate for public utility plants in service.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesPropertyPlantAndEquipmentDisclosureOfCompositeDepreciationRateForPlantsInService
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Useful life of utility generation assets owned by public utility, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesPropertyPlantAndEquipmentGenerationUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Useful life of utility transmission and distribution equipment owned by public utility, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesPropertyPlantAndEquipmentTransmissionAndDistributionUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- 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.

+ Details

Name:	us-gaap_PublicUtilityPropertyPlantAndEquipmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	dei_LegalEntityAxis=he_HamakuaEnergyPartnersLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: