XML 58 R43.htm IDEA: XBRL DOCUMENT
v3.25.2

FAIR VALUE - Recurring Fair Value Measures (Details) - USD ($) $ in Millions | Jun. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Liabilities |  |
Aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year | $ 1.1 |
Aggregate amount of available-for-sale corporate and governmental debt securities maturing after one year through three years | 2.9 |
Aggregate amount of available-for-sale corporate and governmental debt securities maturing after one year through three years after three years through five years | 0.9 |
Aggregate amount of available-for-sale corporate and governmental debt securities maturing after one year through three years after three years through five years after five years | 0.5 |
Recurring Fair Value Measures |  |
Investments |  |
Available-for-sale – Equity Securities | 5.0 | $ 8.6
Available-for-sale – Corporate and Governmental Debt Securities | 5.4 | 6.8
Cash Equivalents | 16.5 | 8.5
Total Fair Value of Assets | 26.9 | 23.9
Liabilities |  |
Deferred Compensation | 20.8 | 21.1
Total Fair Value of Liabilities | 20.8 | 21.1
Recurring Fair Value Measures | Level 1 |  |
Investments |  |
Available-for-sale – Equity Securities | 5.0 | 8.6
Available-for-sale – Corporate and Governmental Debt Securities | 0.0 | 0.0
Cash Equivalents | 16.5 | 8.5
Total Fair Value of Assets | 21.5 | 17.1
Liabilities |  |
Deferred Compensation | 0.0 | 0.0
Total Fair Value of Liabilities | 0.0 | 0.0
Recurring Fair Value Measures | Level 2 |  |
Investments |  |
Available-for-sale – Equity Securities | 0.0 | 0.0
Available-for-sale – Corporate and Governmental Debt Securities | 5.4 | 6.8
Cash Equivalents | 0.0 | 0.0
Total Fair Value of Assets | 5.4 | 6.8
Liabilities |  |
Deferred Compensation | 20.8 | 21.1
Total Fair Value of Liabilities | 20.8 | 21.1
Recurring Fair Value Measures | Level 3 |  |
Investments |  |
Available-for-sale – Equity Securities | 0.0 | 0.0
Available-for-sale – Corporate and Governmental Debt Securities | 0.0 | 0.0
Cash Equivalents | 0.0 | 0.0
Total Fair Value of Assets | 0.0 | 0.0
Liabilities |  |
Deferred Compensation | 0.0 | 0.0
Total Fair Value of Liabilities | $ 0.0 | $ 0.0

X
- Definition Amount of available-for-sale debt securities at fair value maturing in after the fifth fiscal year following the latest fiscal year (maturing in five years or more). + References No definition available. + Details
Name: | ale_AvailableForSaleSecuritiesDebtMaturitiesAfterFiveYearsFairValue
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of available-for-sale debt securities at fair value maturing after the first fiscal year through the third fiscal year following the latest fiscal year (maturing in more than one year to less than three years). + References No definition available. + Details
Name: | ale_AvailableForSaleSecuritiesDebtMaturitiesAfterOneYearThroughThreeYearsFairValue
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of available-for-sale debt securities at fair value maturing after the third fiscal year through the fifth fiscal year following the latest fiscal year (maturing in three years to less than five years). + References No definition available. + Details
Name: | ale_AvailableForSaleSecuritiesDebtMaturitiesAfterThreeYearsThroughFiveYearsFairValue
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This element represents the portion of the balance sheet assertion, Deferred Compensation, valued at fair value by the entity. + References No definition available. + Details
Name: | ale_DeferredCompensationFairValueDisclosure
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Fair value portion of asset recognized for present right to economic benefit. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 55 -Paragraph 100 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482078/820-10-55-100 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_AssetsFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Fair value of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481800/320-10-50-3 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 942 -SubTopic 320 -Name Accounting Standards Codification -Section 50 -Paragraph 3A -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477268/942-320-50-3A + Details
Name: | us-gaap_AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as noncurrent. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481830/320-10-45-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(12)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479130/326-30-45-1 + Details
Name: | us-gaap_AvailableForSaleSecuritiesDebtSecuritiesNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as noncurrent. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1A -Publisher FASB -URI https://asc.fasb.org/1943274/2147482736/825-10-45-1A + Details
Name: | us-gaap_EquitySecuritiesFVNINoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_InvestmentsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 820 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147482106/820-10-50-2 + Details
Name: | us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_LiabilitiesFairValueDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of noncurrent assets that are pledged or subject to withdrawal restrictions, classified as other. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 954 -SubTopic 210 -Name Accounting Standards Codification -Section 45 -Paragraph 4 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477220/954-210-45-4 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 954 -SubTopic 210 -Name Accounting Standards Codification -Section 50 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org/1943274/2147478600/954-210-50-2 + Details
Name: | us-gaap_OtherRestrictedAssetsNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |