Property, Plant and Equipment (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment – Net		$ 5,004.0	$ 5,087.5
Asset Retirement Obligation [Roll Forward]
Beginning Obligation		184.5	166.6
Accretion		9.5	8.8
Liabilities Recognized		7.8	4.5
Liabilities Settled		(4.4)	(5.2)
Revisions in Estimated Cash Flows		3.0	9.8
Ending Obligation		200.4	184.5
Regulated Operations [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment in Service		5,198.6	5,028.7
Construction Work in Progress		74.0	108.7
Accumulated Depreciation		(1,972.3)	(1,834.6)
Property, Plant and Equipment – Net		$ 3,300.3	3,302.8
Regulated Operations [Member] | Generation [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		1 year
Regulated Operations [Member] | Generation [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		50 years
Regulated Operations [Member] | Transmission [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		50 years
Regulated Operations [Member] | Transmission [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		75 years
Regulated Operations [Member] | Distribution [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		18 years
Regulated Operations [Member] | Distribution [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		70 years
ALLETE Clean Energy [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment in Service		$ 1,619.4	1,704.2
Construction Work in Progress		51.1	79.9
Accumulated Depreciation		(176.8)	(149.0)
Property, Plant and Equipment – Net		$ 1,493.7	1,635.1
ALLETE Clean Energy [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		5 years
ALLETE Clean Energy [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		35 years
Corporate and Other [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment in Service	[1]	$ 295.2	267.1
Construction Work in Progress	[1]	50.9	19.8
Accumulated Depreciation	[1]	(136.1)	(137.3)
Property, Plant and Equipment – Net	[1]	$ 210.0	$ 149.6
Corporate and Other [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		3 years
Corporate and Other [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated Useful Lives		50 years

[1] Primarily includes BNI Energy and a small amount of non-rate base generation.