Consolidated Balance Sheet - USD ($)	Dec. 31, 2022	Dec. 31, 2021
Current Assets [Abstract]
Cash and Cash Equivalents	$ 36,400,000	$ 45,100,000
Accounts Receivable, Allowance	137,900,000	123,700,000
Inventories – Net	455,900,000	97,700,000
Prepayments and Other	87,800,000	24,800,000
Total Current Assets	718,000,000.0	291,300,000
Property, Plant and Equipment – Net	5,004,000,000	5,087,500,000
Regulatory Assets	441,000,000.0	511,800,000
Equity Investments	322,700,000	318,000,000.0
Goodwill and Intangible Assets – Net	155,600,000	800,000
Other Non-Current Assets	204,300,000	212,900,000
Total Assets	6,845,600,000	6,422,300,000
Current Liabilities [Abstract]
Accounts Payable	103,000,000.0	111,000,000.0
Accrued Taxes	69,100,000	65,100,000
Accrued Interest	20,500,000	20,100,000
Long-Term Debt Due Within One Year	272,600,000	214,200,000
Other	251,000,000.0	133,000,000.0
Total Current Liabilities	716,200,000	543,400,000
Long-Term Debt	1,648,200,000	1,763,200,000
Deferred Income Taxes	158,100,000	181,800,000
Regulatory Liabilities	526,100,000	536,100,000
Defined Benefit Pension and Other Postretirement Benefit Plans	179,700,000	179,500,000
Other Non-Current Liabilities	269,000,000.0	280,800,000
Total Liabilities	3,497,300,000	3,484,800,000
Commitments, Guarantees and Contingencies (Note 9)
ALLETE Equity [Abstract]
Common Stock Without Par Value, 80.0 Shares Authorized, 57.2 and 53.2 Shares Issued and Outstanding	1,781,500,000	1,536,700,000
Accumulated Other Comprehensive Loss	(24,400,000)	(23,800,000)
Retained Earnings	934,800,000	891,400,000
Total ALLETE Equity	2,691,900,000	2,404,300,000
Non-Controlling Interest in Subsidiaries	656,400,000	533,200,000
Total Equity	3,348,300,000	2,937,500,000
Total Liabilities and Equity	$ 6,845,600,000	$ 6,422,300,000