XML 86 R65.htm IDEA: XBRL DOCUMENT
v3.22.0.1

Short-Term and Long-Term Debt - Long-Term Debt (Details) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jan. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) Years | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
Debt Instrument [Line Items] |  |  |  |
Long-Term Debt |  | $ 1,763.2 | $ 1,593.2 |
Long-Term Debt - Unamortized Debt Issuance Costs |  | 8.8 |  |
Debt Instrument [Abstract] |  |  |  |
Long-Term Debt Maturing in 2022 |  | 214.5 |  |
Long-Term Debt Maturing in 2023 |  | 89.7 |  |
Long-Term Debt Maturing in 2024 |  | 74.4 |  |
Long-Term Debt Maturing in 2025 |  | 386.7 |  |
Long-Term Debt Maturing in 2026 |  | 77.2 |  |
Long-Term Debt Maturing Thereafter |  | 1,143.9 |  |
Proceeds from Non-Controlling Interest - Net of Issuance Costs |  | 90.9 | $ 414.5 | $ 103.8
Camp Ripley Financing [Member] |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Annual Financing Payment |  | $ 1.4 |  |
Financing Renewal Term (Years) | Years |  | 2 |  |
Purchase Option |  | $ 4.0 |  |
First Mortgage Bonds - 2.50% Due August 2030 [Member] |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Interest Rate |  | 4.08% |  |
First Mortgage Bonds - 4.47% Series Due 2049 [Member] |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Interest Rate |  | 4.47% |  |
First Mortgage Bonds - 4.07% Series Due 2048 [Member] |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Interest Rate |  | 4.07% |  |
ALLETE Senior Unsecured Notes 3.11% Due 2027 [Member] |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Interest Rate |  | 3.11% |  |
First Mortgage Bonds - 2.50% Series Due 2030 |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Interest Rate |  | 2.50% |  |
First Mortgage Bonds - 3.30% Series Due 2050 |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Interest Rate |  | 3.30% |  |
Unsecured Term Loan Due In 2022 |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Unsecured Term Loan, Amount |  | $ 150.0 |  |
Debt Instrument, Description of Variable Rate Basis |  | LIBOR |  |
Debt Instrument, Basis Spread on Variable Rate |  | 0.75% |  |
Debt Drawn Through Accordion Feature |  | $ 35.0 |  |
Unsecured Debt, Total Drawn on Loan |  | 185.0 |  |
ALLETE Bonds 2.79% Series Due 2031 |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Proceeds from Issuance of First Mortgage Bond |  | $ 100.0 |  |
Interest Rate |  | 2.79% |  |
Subsequent Event [Member] | Caddo [Member] |  |  |  |
Debt Instrument [Abstract] |  |  |  |
Proceeds from Non-Controlling Interest - Net of Issuance Costs | $ 183.0 |  |  |

X
- Definition Debt Drawn Through Accordion Feature + References No definition available. + Details
Name: | ale_DebtDrawnThroughAccordionFeature
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Renewal term for a debt instrument disclosing for what period of time after maturity the instrument may be extended. + References No definition available. + Details
Name: | ale_DebtInstrumentRenewalTerm
Namespace Prefix: | ale_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Purchase option to acquire an asset. + References No definition available. + Details
Name: | ale_PurchaseOptionAsset
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Unsecured Debt, Total Drawn on Loan + References No definition available. + Details
Name: | ale_UnsecuredDebtTotalDrawnOnLoan
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Unsecured Term Loan, Amount + References No definition available. + Details
Name: | ale_UnsecuredTermLoanAmount
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage points added to the reference rate to compute the variable rate on the debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Description of reference rate used for variable rate of debt instrument. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1B -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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

X
- Definition Amount of the required periodic payments including both interest and principal payments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=123599511&loc=d3e64711-112823 + Details
Name: | us-gaap_DebtInstrumentPeriodicPayment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=124435984&loc=d3e28555-108399 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_DeferredFinanceCostsNoncurrentNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing after fifth 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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=123465755&loc=d3e1835-112601 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1E -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalAfterYearFive
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and 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 -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1E -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=123465755&loc=d3e1835-112601 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextTwelveMonths
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in fifth 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 -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1E -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=123465755&loc=d3e1835-112601 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in fourth 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 -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1E -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=123465755&loc=d3e1835-112601 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in third 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 -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1E -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=123465755&loc=d3e1835-112601 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of long-term debt payable, sinking fund requirement, and other securities issued that are redeemable by holder at fixed or determinable price and date, maturing in second 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 -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 1E -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04(a)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e24072-122690 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=123465755&loc=d3e1835-112601 + Details
Name: | us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_LongTermDebtNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The cash inflow from amounts received from a long-term debt instrument secured by a first mortgage deed of trust, containing a pledge of real property. The lender has the highest claim on the property in case of default. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585 + Details
Name: | us-gaap_ProceedsFromIssuanceOfFirstMortgageBond
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of cash inflow from a noncontrolling interest. Includes, but is not limited to, purchase of additional shares or other increase in noncontrolling interest ownership. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=123570139&loc=d3e3255-108585 + Details
Name: | us-gaap_ProceedsFromMinorityShareholders
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_DebtInstrumentAxis=ale_CampRipleyFinancingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=ale_ALLETEBonds4.08DueMarch2029Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=ale_ALLETEBonds4.47DueMarch2049Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=ale_ALLETEBonds4.07DueApril2048Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=ale_ALLETESeniorUnsecuredNotes3.11Due2027Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=ale_ALLETEBonds250DueAugust2030Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=ale_ALLETEBonds330DueAugust2050Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=ale_UnsecuredTermLoanDueIn2022Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=ale_ALLETEBonds279SeriesDueSeptember2031Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_CreditFacilityAxis=ale_CaddoMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |