Consolidated Balance Sheet - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Current Assets [Abstract]
Cash and Cash Equivalents	$ 29.9	$ 36.4
Accounts Receivable (Less Allowance of $1.7 and $1.6)	120.3	137.9
Inventories – Net	346.9	455.9
Prepayments and Other	72.6	87.8
Total Current Assets	569.7	718.0
Property, Plant and Equipment – Net	4,979.3	5,004.0
Regulatory Assets	469.1	441.0
Equity Investments	323.9	322.7
Goodwill and Intangible Assets - Net	155.5	155.6
Other Non-Current Assets	207.0	204.3
Total Assets	6,704.5	6,845.6
Current Liabilities [Abstract]
Accounts Payable	84.9	103.0
Accrued Taxes	81.4	69.1
Accrued Interest	14.9	20.5
Long-Term Debt Due Within One Year	176.4	272.6
Other	106.8	251.0
Total Current Liabilities	464.4	716.2
Long-Term Debt	1,755.5	1,648.2
Deferred Income Taxes	156.3	158.1
Regulatory Liabilities	526.4	526.1
Defined Benefit Pension and Other Postretirement Benefit Plans	173.8	179.7
Other Non-Current Liabilities	270.4	269.0
Total Liabilities	3,346.8	3,497.3
Commitments, Guarantees and Contingencies (Note 6)
Equity [Abstract]
Common Stock Without Par Value, 80.0 Shares Authorized, 57.3 and 57.2 Shares Issued and Outstanding	1,785.6	1,781.5
Accumulated Other Comprehensive Loss	(24.3)	(24.4)
Retained Earnings	954.2	934.8
Total ALLETE Equity	2,715.5	2,691.9
Non-Controlling Interest in Subsidiaries	642.2	656.4
Total Equity	3,357.7	3,348.3
Total Liabilities and Equity	$ 6,704.5	$ 6,845.6