Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment and Estimated Useful Lives of Property, Plant and Equipment [Table Text Block]

Property, Plant and Equipment
As of December 31	2020	2019
Millions
Regulated Operations
Property, Plant and Equipment in Service	$4,972.3	$4,555.8
Construction Work in Progress	79.4	383.6
Accumulated Depreciation	(1,758.0)	(1,635.3)
Regulated Operations – Net	3,293.7	3,304.1
ALLETE Clean Energy
Property, Plant and Equipment in Service	1,275.4	686.0
Construction Work in Progress	261.0	351.3
Accumulated Depreciation	(112.9)	(86.8)
ALLETE Clean Energy – Net	1,423.5	950.5
Corporate and Other (a)
Property, Plant and Equipment in Service	240.5	231.9
Construction Work in Progress	9.6	3.8
Accumulated Depreciation	(126.5)	(113.3)
Corporate and Other – Net	123.6	122.4
Property, Plant and Equipment – Net	$4,840.8	$4,377.0

(a)Primarily includes BNI Energy and a small amount of non-rate base generation.

Estimated Useful Lives of Property, Plant and Equipment (Years)
Regulated Operations
Generation	3 to 50	ALLETE Clean Energy	5 to 35
Transmission	52 to 71	Corporate and Other	3 to 50
Distribution	19 to 68

Asset Retirement Obligations [Table Text Block]

Asset Retirement Obligations
Millions
Obligation as of December 31, 2018	$138.6
Accretion	7.2
Liabilities Recognized	1.4
Liabilities Settled	(4.6)
Revisions in Estimated Cash Flows	17.7
Obligation as of December 31, 2019	160.3
Accretion	8.3
Liabilities Recognized	1.4
Liabilities Settled	(3.6)
Revisions in Estimated Cash Flows	0.2
Obligation as of December 31, 2020	$166.6