XML 82 R67.htm IDEA: XBRL DOCUMENT
v3.22.4

Actual Investment Allocations (Detail) | Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
--- | --- | --- | --- | ---
Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 100.00% | 100.00% | 100.00%
Pension Plans | Equity Funds |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 53.00% | 57.00% | 58.00%
Pension Plans | Fixed Income Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 38.00% | 38.00% | 37.00%
Pension Plans | Other |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation | [1] |  | 2.00% | 1.00% | 1.00%
Other Postretirement Benefit Plans, Defined Benefit |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 100.00% | 100.00% | 100.00%
Other Postretirement Benefit Plans, Defined Benefit | Equity Funds |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 55.00% | 56.00% | 55.00%
Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 45.00% | 44.00% | 45.00%
Real Estate Funds | Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Actual Allocation |  |  | 7.00% | 4.00% | 4.00%
Scenario Forecast | Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 56.00% |  |  |
Scenario Forecast | Pension Plans | Equity Funds |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 56.00% |  |  |
Scenario Forecast | Pension Plans | Fixed Income Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 39.00% |  |  |
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Equity Funds |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 55.00% |  |  |
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 45.00% |  |  |
Scenario Forecast | Real Estate Funds | Pension Plans |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |
Target Allocation |  | 5.00% |  |  |
[1] | Represents investments being held in cash equivalents as of December 31, 2022, December 31, 2021 and December 31, 2020 pending payment of benefits.

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_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI https://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_EquityFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_FixedIncomeSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=utl_OtherFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_InvestmentTypeAxis=us-gaap_RealEstateFundsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |