XML 54 R41.htm IDEA: XBRL DOCUMENT
v3.20.2

Equity Investments - Investment in ATC (Details) - USD ($) $ in Millions |  | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
Jul. 31, 2020 | Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
ALLETE's Investment in ATC [Roll Forward] |  |  |  |  |  |
Equity Investment Balance as of December 31, 2019 |  |  |  |  | $ 197.6 |
Cash Investments |  |  |  |  | 66.6 | $ 4.6
Equity in ATC Earnings (a) |  |  | $ 6.4 | $ 4.8 | 11.6 | $ 10.4
Equity Investment Balance as of June 30, 2020 |  |  | $ 267.1 |  | $ 267.1 |
ATC [Member] |  |  |  |  |  |
Investment in ATC [Line Items] |  |  |  |  |  |
Ownership Percentage |  |  | 8.00% |  | 8.00% |
Expected Additional Investment in 2020 |  |  | $ 0.8 |  | $ 0.8 |
ALLETE's Investment in ATC [Roll Forward] |  |  |  |  |  |
Equity Investment Balance as of December 31, 2019 |  |  |  |  | 141.6 |
Cash Investments |  |  |  |  | 1.1 |
Equity in ATC Earnings (a) | [1] |  |  |  | 11.6 |
Distributed ATC Earnings |  |  |  |  | (9.4) |
Amortization of the Remeasurement of Deferred Income Taxes |  |  |  |  | 0.7 |
Equity Investment Balance as of June 30, 2020 |  |  | $ 145.6 |  | $ 145.6 |
Authorized Return on Equity |  |  |  |  | 10.02% |
Authorized Return on Equity, Including Incentive Adder |  |  | 10.52% |  | 10.52% |
Additional Equity in Earnings During the Period |  |  |  |  | $ 1.2 |
ATC [Member] | Subsequent Event [Member] |  |  |  |  |  |
ALLETE's Investment in ATC [Roll Forward] |  |  |  |  |  |
Cash Investments |  | $ 0.8 |  |  |  |
[1] | Equity in ATC Earnings includes $1.2 million of additional earnings resulting from the FERC’s May 21, 2020, order increasing ATC’s authorized return on equity to 10.52 percent including an incentive adder for participation in a regional transmission organization.

X
- Definition Additional Equity in Earnings During the Period + References No definition available. + Details
Name: | ale_AdditionalEquityInEarningsDuringThePeriod
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition ALLETE's Investment in ATC [Roll Forward] + References No definition available. + Details
Name: | ale_AlletesInvestmentInAtcRollForward
Namespace Prefix: | ale_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amortization from the Remeasurement of Deferred Income Taxes for Equity Method Investments + References No definition available. + Details
Name: | ale_AmortizationfromtheRemeasurementofDeferredIncomeTaxesforEquityMethodInvestments
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The approved percentage return on common equity, including an incentive adder for participation in a regional transmission organization dedicated to the utility plant in the investee accounted for under the equity method of accounting. + References No definition available. + Details
Name: | ale_EquityMethodInvestmentApprovedReturnonCommonEquityIncludingIncentiveAdder
Namespace Prefix: | ale_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Additional investments expected to be made during the current fiscal year but after the filing date, not already separately disclosed as part of current period/year-to-date investments or as a subsequent event. + References No definition available. + Details
Name: | ale_EquityMethodInvestmentExpectedAdditionalInvestment
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(10)) -URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(12)) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 21D -URI http://asc.fasb.org/extlink&oid=121586364&loc=SL94080555-108585 + Details
Name: | us-gaap_EquityMethodInvestmentDividendsOrDistributions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 + Details
Name: | us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 25 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8813-108599 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
Name: | us-gaap_EquityMethodInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of income (loss) for proportionate share of equity method investee's income (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03(12)) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(10)) -URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(13)(f)) -URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 280 -SubTopic 10 -Section 50 -Paragraph 22 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599 Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570 + Details
Name: | us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3213-108585 + Details
Name: | us-gaap_PaymentsToAcquireEquityMethodInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Percentage of public utility's approved return on equity. + References No definition available. + Details
Name: | us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
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_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ale_ATCMember
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: |