Average demand measured for a specified customer, measured in MW.

No definition available.

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- Definition

Estimated Annual Reduction to Revenue Due to Idled Customers net of associated expense savings such as fuel costs.

+ References

No definition available.

+ Details

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Namespace Prefix:	ale_
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- Definition

Forced Outage Costs

+ References

No definition available.

+ Details

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Balance Type:	debit
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- Definition

The length of notice required to terminate a contract (in years).

+ References

No definition available.

+ Details

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- Definition

Number of Customers

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Proposed Ongoing Customer Rate Increase

+ References

No definition available.

+ Details

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Namespace Prefix:	ale_
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Period Type:	duration

- Definition

Public Utilities Reserve for Interim Rates (Recorded During Period)

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Percentage of public utility's approved equity to capital, including debt and equity.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Amount of public utility's approved rate increase (decrease) by regulatory agency.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Percentage of public utility's approved return on equity.

+ References

No definition available.

+ Details

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- 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

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- Definition

Amount of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Percentage of public utility's interim rate increase (decrease) allowed while waiting final decision of regulatory agency.

+ References

No definition available.

+ Details

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- Definition

Percentage of public utility's requested equity to capital, including debt and equity.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Amount of public utility's requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

Percentage of public utility's requested rate increase (decrease) with regulatory agency.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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- Definition

Percentage of public utility's requested return on equity.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of regulated other operating revenues recognized during the period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Details

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- Details

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Regulatory Matters - Electric Rates (Details) $ in Millions		3 Months Ended	4 Months Ended	8 Months Ended	12 Months Ended			18 Months Ended
Regulatory Matters - Electric Rates (Details) $ in Millions	Dec. 20, 2018	Jun. 30, 2020 USD ($)	Apr. 30, 2020	Dec. 31, 2020 Years Customers	Dec. 31, 2020 USD ($) Years Customers	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Jun. 30, 2019 MW
MPUC [Member] \| Fuel Adjustment Clause Filing [Member] \| Minnesota Power [Member]
Regulatory Matters [Line Items]
Forced Outage Costs								$ 8.0
MPUC [Member] \| COVID-19 Related Deferred Accounting [Member] \| Minnesota Power [Member]
Regulatory Matters [Line Items]
Estimated Annual Reduction to Revenue Due to Idled Customers					$ 30.0
PSCW [Member] \| 2018 Wisconsin General Rate Case [Member] \| SWL&P [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Approved Return on Common Equity	10.40%
Approved Equity Ratio	55.00%
Approved Rate Increase - Amount					3.0
Electric Rates [Member] \| MPUC [Member] \| Minnesota Cost Recovery Riders [Member] \| Minnesota Power [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Revenue from Cost Recovery Riders					$ 29.9	$ 31.8	$ 103.8
Electric Rates [Member] \| MPUC [Member] \| 2020 Minnesota General Rate Review [Member] \| Minnesota Power [Member] \| Retail Customers [Member]
Regulatory Matters [Line Items]
Requested Average Rate Increase					10.60%
Requested Return on Equity					10.05%
Requested Equity Ratio					53.81%
Annual Additional Revenue Generated from Requested Final Rate Increase					$ 66.0
Public Utilities, Interim Rate Increase (Decrease), Amount					$ 36.1
Proposed Ongoing Customer Rate Increase				4.10%
Public Utilities, Interim Rate Increase (Decrease), Percentage			5.80%
Public Utilities Reserve for Interim Rates (Recorded During Period)		$ 11.7
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member]
Regulatory Matters [Line Items]
Number of Customers \| Customers				15	15
Notice Required to Terminate (Years) \| Years				3	3
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member] \| Wholesale Electric Contract (Cost-Based Formula Methodology for Entire Term) [Member]
Regulatory Matters [Line Items]
Number of Customers \| Customers				2	2
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member] \| Wholesale Electric Contracts (expire December 2024) [Member]
Regulatory Matters [Line Items]
Number of Customers \| Customers				14	14
Electric Rates [Member] \| FERC [Member] \| FERC-Approved Wholesale Rates [Member] \| Minnesota Power [Member] \| Municipal Customers [Member] \| Wholesale Electric Contract (Termination Effective June 2019) [Member]
Regulatory Matters [Line Items]
Average Customer Demand (MW) \| MW									29