Consolidated Balance Sheet - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Current Assets [Abstract]
Cash and Cash Equivalents	$ 47.9	$ 36.4
Accounts Receivable (Less Allowance of $1.6 and $1.6)	123.2	137.9
Inventories – Net	194.3	455.9
Prepayments and Other	80.8	87.8
Total Current Assets	446.2	718.0
Property, Plant and Equipment – Net	4,973.9	5,004.0
Regulatory Assets	454.5	441.0
Equity Investments	327.5	322.7
Goodwill and Intangible Assets - Net	155.5	155.6
Other Non-Current Assets	210.3	204.3
Total Assets	6,567.9	6,845.6
Current Liabilities [Abstract]
Accounts Payable	89.3	103.0
Accrued Taxes	50.4	69.1
Accrued Interest	21.3	20.5
Long-Term Debt Due Within One Year	106.7	272.6
Other	112.6	251.0
Total Current Liabilities	380.3	716.2
Long-Term Debt	1,685.9	1,648.2
Deferred Income Taxes	153.6	158.1
Regulatory Liabilities	538.0	526.1
Defined Benefit Pension and Other Postretirement Benefit Plans	173.6	179.7
Other Non-Current Liabilities	268.0	269.0
Total Liabilities	3,199.4	3,497.3
Commitments, Guarantees and Contingencies (Note 6)
Equity [Abstract]
Common Stock Without Par Value, 80.0 Shares Authorized, 57.4 and 57.2 Shares Issued and Outstanding	1,791.6	1,781.5
Accumulated Other Comprehensive Loss	(24.4)	(24.4)
Retained Earnings	966.9	934.8
Total ALLETE Equity	2,734.1	2,691.9
Non-Controlling Interest in Subsidiaries	634.4	656.4
Total Equity	3,368.5	3,348.3
Total Liabilities and Equity	$ 6,567.9	$ 6,845.6