XML 45 R32.htm IDEA: XBRL DOCUMENT
v3.22.2.2

Operations and Significant Accounting Policies (Details) - USD ($) $ in Millions | Sep. 30, 2022 | Dec. 31, 2021 | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | --- | --- | ---
Cash, Cash Equivalents and Restricted Cash [Abstract] |  |  |  |  |
Cash and Cash Equivalents |  | $ 42.1 | $ 45.1 | $ 59.0 | $ 44.3
Restricted Cash included in Prepayments and Other |  | 4.2 | 0.3 | 4.1 | 0.8
Restricted Cash included in Other Non-Current Assets |  | 2.3 | 2.3 | 2.3 | 20.1
Cash, Cash Equivalents and Restricted Cash on the Consolidated Statement of Cash Flows |  | 48.6 | 47.7 | 65.4 | 65.2
Inventories – Net [Abstract] |  |  |  |  |
Fuel | [1] | 36.2 | 18.7 |  |
Materials and Supplies |  | 70.6 | 56.1 |  |
Renewable Energy Facilities Under Development | [2] | 365.4 | 22.9 |  |
Total Inventories – Net |  | 472.2 | 97.7 |  |
Other Non-Current Assets [Abstract] |  |  |  |  |
Contract Assets | [3] | 21.5 | 23.3 |  |
Operating Lease, Right-of-Use Asset |  | 13.9 | 16.4 |  |
ALLETE Properties |  | 17.6 | 19.4 |  |
Restricted Cash, Non-Current |  | 2.3 | 2.3 | $ 2.3 | $ 20.1
Other Postretirement Benefit Plans |  | 66.5 | 64.8 |  |
Other |  | 79.8 | 86.7 |  |
Total Other Non-Current Assets |  | 201.6 | 212.9 |  |
Other Current Liabilites [Abstract] |  |  |  |  |
Customer Deposits | [4] | 111.7 | 27.2 |  |
PSAs |  | 6.1 | 12.6 |  |
Manufactured Gas Plant - Current | [5] | 17.8 | 12.8 |  |
Fuel Adjustment Clause |  | 0.0 | 5.0 |  |
Operating Lease Liabilities |  | 3.7 | 4.8 |  |
Redeemable Non-Controlling Interest | [6] | 0.0 | 30.6 |  |
Other |  | 49.2 | 40.0 |  |
Total Other Current Liabilities |  | 188.5 | 133.0 |  |
Other Non-Current Liabilities [Abstract] |  |  |  |  |
Asset Retirement Obligation | [7] | 197.2 | 184.5 |  |
PSAs |  | 28.4 | 39.5 |  |
Manufactured Gas Plant - Non-Current | [8] | 0.2 | 5.2 |  |
Operating Lease Liabilities |  | 10.0 | 11.6 |  |
Other |  | 33.0 | 40.0 |  |
Total Other Non-Current Liabilities |  | 268.8 | 280.8 |  |
BNI Energy |  |  |  |  |
Business Segments [Line Items] |  |  |  |  |
Other Receivables |  | $ 28.5 | $ 28.5 |  |
[1] | Fuel consists primarily of coal inventory at Minnesota Power.
[2] | Renewable Energy Facilities Under Development consists primarily of project costs related to ALLETE Clean Energy’s Northern Wind, Rock Aetna, and Red Barn wind projects which are expected to be sold in late 2022 and early 2023, respectively. (See Other Current Liabilities.)
[3] | Contract Assets consist of payments made to customers as an incentive to execute or extend service agreements. The contract payments are being amortized over the term of the respective agreements as a reduction to revenue.
[4] | Primarily related to deposits received by ALLETE Clean Energy for the Northern Wind, Rock Aetna and Red Barn wind projects which are expected to be sold in late 2022 and early 2023, respectively. (See Inventories – Net.)
[5] | The manufactured gas plant represents the current liability for remediation of a former manufactured gas plant site located in Superior, Wisconsin, and formerly operated by SWL&P.
[6] | Amount reclassified from Non-Controlling Interest in Subsidiaries resulting from the exercise of an option to buy out a non-controlling interest, which was paid in the first quarter of 2022.
[7] | The asset retirement obligation is primarily related to our Regulated Operations and is funded through customer rates over the life of the related assets. Additionally, BNI Energy funds its obligation through its cost-plus coal supply agreements for which BNI Energy has recorded a receivable of $28.5 million in Other Non-Current Assets on the Consolidated Balance Sheet as of September 30, 2022, ($28.5 million as of December 31, 2021).
[8] | The manufactured gas plant represents the non-current liability for remediation of a former manufactured gas plant site located in Superior, Wisconsin, and formerly operated by SWL&P.

X
- Definition Manufactured Gas Plant - Current + References No definition available. + Details
Name: | ale_ManufacturedGasPlantCurrent
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Manufactured Gas Plant - Non-Current + References No definition available. + Details
Name: | ale_ManufacturedGasPlantNonCurrent
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Other Postretirement Benefit Plans + References No definition available. + Details
Name: | ale_OtherPostretirementBenefitPlans
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The fair value adjustment for the price of power per MW at market rates compared to those at contract rate at the time of acquisition through the end of the contract term present valued to acquisition date resulting in a current liability. + References No definition available. + Details
Name: | ale_PowerPurchaseAgreementCurrentLiability
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The fair value adjustment for the price of power per MW at market rates compared to those at contract rate at the time of acquisition through the end of the contract term present valued to acquisition date resulting in a noncurrent liability. + References No definition available. + Details
Name: | ale_PowerPurchaseAgreementNoncurrentLiability
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Public Utilities, Fuel Adjustment Clause + References No definition available. + Details
Name: | ale_PublicUtilitiesFuelAdjustmentClause
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Redeemable Non-Controlling Interest + References No definition available. + Details
Name: | ale_RedeemableNonControllingInterest
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI https://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
Name: | us-gaap_AssetRetirementObligationsNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3044-108585 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(1)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_CashAndCashEquivalentsAtCarryingValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of cash and cash equivalents, and cash and cash equivalents restricted to withdrawal or usage. Excludes amount for disposal group and discontinued operations. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 24 -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3521-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 4 -URI https://asc.fasb.org/extlink&oid=126954810&loc=d3e3044-108585 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 8 -URI https://asc.fasb.org/extlink&oid=126999549&loc=SL98516268-108586 + Details
Name: | us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as noncurrent. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 3 -URI https://asc.fasb.org/extlink&oid=126919976&loc=SL49130533-203044 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130549-203045 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=126919976&loc=SL49130531-203044 + Details
Name: | us-gaap_ContractWithCustomerAssetNetNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=126919976&loc=SL49130531-203044 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 2 -URI https://asc.fasb.org/extlink&oid=126919976&loc=SL49130532-203044 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130549-203045 + Details
Name: | us-gaap_ContractWithCustomerLiabilityCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Carrying amount as of the balance sheet date of coal, which is a combustible rock or minerals which are extracted from the ground and used as fuel. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(6)(a)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_EnergyRelatedInventoryCoal
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(6)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 55 -Paragraph 10 -URI https://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766 + Details
Name: | us-gaap_InventoryNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of products used directly or indirectly in the manufacturing or production process, which may or may not become part of the final product. May also include items used in the storage, presentation or transportation of physical goods. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 330 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.BB) -URI https://asc.fasb.org/extlink&oid=27011343&loc=d3e100047-122729 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(6)(a)(5)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_InventorySuppliesNetOfReserves
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Present value of lessee's discounted obligation for lease payments from operating lease, classified as current. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977 + Details
Name: | us-gaap_OperatingLeaseLiabilityCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Present value of lessee's discounted obligation for lease payments from operating lease, classified as noncurrent. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977 + Details
Name: | us-gaap_OperatingLeaseLiabilityNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of lessee's right to use underlying asset under operating lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 1 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=123391704&loc=SL77918627-209977 + Details
Name: | us-gaap_OperatingLeaseRightOfUseAsset
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of expenses incurred but not yet paid classified as other, due within one year or the normal operating cycle, if longer. + 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 210.5-02.20) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_OtherAccruedLiabilitiesCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of expenses incurred but not yet paid classified as other, due after one year or the normal operating cycle, if longer. + 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 210.5-02.24) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_OtherAccruedLiabilitiesNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of other miscellaneous assets expected to be realized or consumed after one year or normal operating cycle, if longer. + References No definition available. + Details
Name: | us-gaap_OtherAssetsMiscellaneousNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of noncurrent assets classified as other. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(17)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_OtherAssetsNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Amount before valuation and LIFO reserves of other inventory expected to be sold, or consumed within one year or operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(6)(a)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_OtherInventory
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of liabilities classified as other, due within one year or the normal operating cycle, if longer. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 55 -Paragraph 10 -URI https://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766 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 210.5-02.20) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_OtherLiabilitiesCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Definition Amount of liabilities classified as other, due after one year or the normal operating cycle, if longer. + 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 210.5-02.24) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_OtherLiabilitiesNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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

X
- Definition Amount due from parties in nontrade transactions, classified as other. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(3)(a)(4)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_OtherReceivables
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of real estate investments, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; (7) other real estate investments; (8) real estate joint ventures; and (9) unconsolidated real estate and other joint ventures not separately presented. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1(d)) -URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910 + Details
Name: | us-gaap_RealEstateInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of cash restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 8 -URI https://asc.fasb.org/extlink&oid=126999549&loc=SL98516268-108586 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(1)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_RestrictedCashCurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of cash restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(17)) -URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 50 -Paragraph 8 -URI https://asc.fasb.org/extlink&oid=126999549&loc=SL98516268-108586 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 954 -SubTopic 210 -Section 45 -Paragraph 5 -URI https://asc.fasb.org/extlink&oid=120413173&loc=SL116631458-115580 + Details
Name: | us-gaap_RestrictedCashNoncurrent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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_SegmentReportingInformationLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=ale_BNIEnergyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |