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Property, Plant and Equipment (Tables)
 12 Months Ended
Dec. 31, 2013
Property, Plant and Equipment [Abstract]  
Property, Plant, and Equipment [Table Text Block]
Property, Plant and Equipment
 
 
 
As of December 31
2013
 
2012
Millions
 
 
 
Regulated Utility

$3,380.0

 

$3,232.9

Construction Work in Progress
303.9

 
151.8

Accumulated Depreciation
(1,181.7
)
 
(1,102.8
)
Regulated Utility Plant - Net
2,502.2

 
2,281.9

Non-Rate Base Energy Operations
131.3

 
118.0

Construction Work in Progress
3.4

 
4.2

Accumulated Depreciation
(60.4
)
 
(56.7
)
Non-Rate Base Energy Operations Plant - Net
74.3

 
65.5

Other Plant - Net
—

 
0.2

Property, Plant and Equipment - Net

$2,576.5

 

$2,347.6
Estimated Useful Lives of Property, Plant and Equipment [Table Text Block]
Estimated Useful Lives of Property, Plant and Equipment
Generation
5 to 35 years
 
Distribution
14 to 65 years
Transmission
42 to 61 years
 
Other Plant
5 to 25 years
Asset Retirement Obligation [Table Text Block]
Asset Retirement Obligation
 
 
Millions
 
 
Obligation as of December 31, 2011
 

$57.0

Accretion Expense
 
3.8

Revisions in estimated cash flows
 
17.1

Obligation as of December 31, 2012
 
77.9

Accretion Expense
 
4.6

Revisions in estimated cash flows
 
(0.7
)
Obligation as of December 31, 2013
 

$81.8