Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2014

Property, Plant and Equipment [Abstract]

Property, Plant, and Equipment [Table Text Block]

Property, Plant and Equipment
As of December 31	2014			2013
Millions
Regulated Utility		$3,903.3			$3,380.0
Construction Work in Progress	355.4			303.9
Accumulated Depreciation	(1,260.2		)	(1,181.7		)
Regulated Utility Plant - Net	2,998.5			2,502.2
Investments and Other Operations (a)	357.8			131.3
Construction Work in Progress	5.9			3.4
Accumulated Depreciation	(75.8		)	(60.4		)
Investments and Other Operations Plant - Net	287.9			74.3
Property, Plant and Equipment - Net		$3,286.4			$2,576.5

(a) Includes primarily ALLETE Clean Energy, BNI Coal and a small amount of non-rate base generation.

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

Estimated Useful Lives of Property, Plant and Equipment
Generation	5 to 50 years	Distribution	18 to 65 years
Transmission	44 to 67 years	Investments and Other Operations	5 to 44 years

Asset Retirement Obligation [Table Text Block]

Asset Retirement Obligation
Millions
Obligation as of December 31, 2012		$77.9
Accretion	4.6
Revisions in estimated cash flows	(0.7		)
Obligation as of December 31, 2013	81.8
Accretion	5.5
Liabilities recognized (a)	23.0
Liabilities settled	(0.5		)
Revisions in estimated cash flows	(0.6		)
Obligation as of December 31, 2014		$109.2

(a) The increase in 2014 is primarily related to BNI Coal for coal mining expansion and ALLETE Clean Energy due to wind energy facilities acquisitions.