Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2018

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	2018			2017
Millions
Regulated Operations
Property, Plant and Equipment in Service		$4,490.6			$4,523.7
Construction Work in Progress	251.1			121.6
Accumulated Depreciation	(1,549.6		)	(1,520.5		)
Regulated Operations – Net	3,192.1			3,124.8
ALLETE Clean Energy
Property, Plant and Equipment in Service	488.4			482.5
Construction Work in Progress	164.5			144.9
Accumulated Depreciation	(73.0		)	(60.8		)
ALLETE Clean Energy – Net	579.9			566.6
U.S. Water Services
Property, Plant and Equipment in Service	30.1			24.8
Accumulated Depreciation	(14.0		)	(10.4		)
U.S. Water Services – Net	16.1			14.4
Corporate and Other (a)
Property, Plant and Equipment in Service	214.3			204.7
Construction Work in Progress	6.6			5.0
Accumulated Depreciation	(104.6		)	(93.1		)
Corporate and Other – Net	116.3			116.6
Property, Plant and Equipment – Net		$3,904.4			$3,822.4

(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		ALLETE Clean Energy	5 to 35
Generation	5 to 50	U.S. Water Services	5 to 39
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, 2016		$136.6
Accretion	7.6
Liabilities Settled	(5.9		)
Revisions in Estimated Cash Flows	(15.6		)
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