Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

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

Estimated Useful Lives of Property, Plant and Equipment (Years)
Regulated Operations
Generation	4 to 50	ALLETE Clean Energy	5 to 35
Transmission	52 to 71	Corporate and Other	3 to 50
Distribution	19 to 68

Property, Plant and Equipment
As of December 31	2019			2018
Millions
Regulated Operations
Property, Plant and Equipment in Service		$4,555.8			$4,490.6
Construction Work in Progress	383.6			251.1
Accumulated Depreciation	(1,635.3		)	(1,549.6		)
Regulated Operations – Net	3,304.1			3,192.1
ALLETE Clean Energy
Property, Plant and Equipment in Service	686.0			488.4
Construction Work in Progress	351.3			164.5
Accumulated Depreciation	(86.8		)	(73.0		)
ALLETE Clean Energy – Net	950.5			579.9
U.S. Water Services (a)
Property, Plant and Equipment in Service	—			30.1
Accumulated Depreciation	—			(14.0		)
U.S. Water Services – Net	—			16.1
Corporate and Other (b)
Property, Plant and Equipment in Service	231.9			214.3
Construction Work in Progress	3.8			6.6
Accumulated Depreciation	(113.3		)	(104.6		)
Corporate and Other – Net	122.4			116.3
Property, Plant and Equipment – Net		$4,377.0			$3,904.4

(a) On March 26, 2019, ALLETE completed the sale of U.S. Water Services. (See Note 1. Operations and Significant Accounting Policies.)

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

Asset Retirement Obligations [Table Text Block]

Asset Retirement Obligations
Millions
Obligation as of December 31, 2017		$122.7
Accretion	7.0
Liabilities Settled	(5.3		)
Revisions in Estimated Cash Flows	14.2
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