Debt Drawn Through Accordion Feature

No definition available.

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- Definition

Renewal term for a debt instrument disclosing for what period of time after maturity the instrument may be extended.

+ References

No definition available.

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Period Type:	instant

- Definition

Purchase option to acquire an asset.

+ References

No definition available.

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- Definition

Unsecured Debt, Total Drawn on Loan

+ References

No definition available.

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- Definition

Unsecured Term Loan, Amount

+ References

No definition available.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

Description of reference rate used for variable rate of debt instrument.

+ References

No definition available.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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Balance Type:	na
Period Type:	instant

- 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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Balance Type:	na
Period Type:	duration

- Definition

Amount of the required periodic payments including both interest and principal payments.

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Balance Type:	debit
Period Type:	duration

- 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.

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- References

No definition available.

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- 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).

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- 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).

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- 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).

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- 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).

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- 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

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- 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

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- 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

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- 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.

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- 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.

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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