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Property, Plant and Equipment (Tables)
 12 Months Ended
Dec. 31, 2011
Property, Plant and Equipment [Abstract]  
Property, Plant, and Equipment [Table Text Block]
Property, Plant and Equipment
 
 
 
As of December 31
2011
 
2010
Millions
 
 
 
Regulated Utility

$2,794.8

 

$2,649.2

Construction Work in Progress
155.0

 
86.6

Accumulated Depreciation
(1,024.6
)
 
(975.8
)
Regulated Utility Plant - Net
1,925.2

 
1,760.0

Non-Rate Base Energy Operations
106.4

 
88.4

Construction Work-in-Progress
2.3

 
4.5

Accumulated Depreciation
(51.4
)
 
(48.0
)
Non-Rate Base Energy Operations Plant - Net
57.3

 
44.9

Other Plant - Net
0.2

 
0.7

Property, Plant and Equipment - Net

$1,982.7

 

$1,805.6
Estimated Useful Lives of Property, Plant and Equipment [Table Text Block]
Estimated Useful Lives of Property, Plant and Equipment
 
 
 
 
 
Regulated Utility –
Generation
4 to 35 years
Non-Rate Base Operations
3 to 61 years
 
Transmission
42 to 61 years
Other Plant
5 to 25 years
 
Distribution
14 to 65 years
 
 
Asset Retirement Obligation [Table Text Block]
Asset Retirement Obligation
 
 
Millions
 
 
Obligation as of December 31, 2009
 

$44.6

Accretion Expense
 
2.9

Additional Liabilities Incurred in 2010
 
2.8

Obligation as of December 31, 2010
 
50.3

Accretion Expense
 
6.4

Additional Liabilities Incurred in 2011
 
0.3

Obligation as of December 31, 2011
 

$57.0