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Property, Plant and Equipment
12 Months Ended
Dec. 31, 2012
Property, Plant and Equipment [Abstract]  
Property, Plant and Equipment [Text Block]
PROPERTY, PLANT AND EQUIPMENT

Property, Plant and Equipment
 
 
 
As of December 31
2012
 
2011
Millions
 
 
 
Regulated Utility

$3,232.9

 

$2,794.8

Construction Work in Progress
151.8

 
155.0

Accumulated Depreciation
(1,102.8
)
 
(1,024.6
)
Regulated Utility Plant - Net
2,281.9

 
1,925.2

Non-Rate Base Energy Operations
118.0

 
106.4

Construction Work in Progress
4.2

 
2.3

Accumulated Depreciation
(56.7
)
 
(51.4
)
Non-Rate Base Energy Operations Plant - Net
65.5

 
57.3

Other Plant - Net
0.2

 
0.2

Property, Plant and Equipment - Net

$2,347.6

 

$1,982.7


Depreciation is computed using the straight-line method over the estimated useful lives of the various classes of assets.

Estimated Useful Lives of Property, Plant and Equipment
 
 
 
 
 
Regulated Utility –
Generation
3 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 Obligations. We recognize, at fair value, obligations associated with the retirement of certain tangible, long-lived assets that result from the acquisition, construction or development and/or normal operation of the asset. Asset retirement obligations (ARO) relate primarily to the decommissioning of our coal-fired and wind generating facilities and land reclamation at BNI Coal, and are included in other non-current liabilities on our Consolidated Balance Sheet. The associated retirement costs are capitalized as part of the related long-lived asset and depreciated over the useful life of the asset. Removal costs associated with certain distribution and transmission assets have not been recognized, as these facilities have indeterminate useful lives.

Conditional asset retirement obligations have been identified for treated wood poles and remaining polychlorinated biphenyl and asbestos-containing assets; however, removal costs have not been recognized because they are considered immaterial to our consolidated financial statements.

Long-standing ratemaking practices approved by applicable state and federal regulatory commissions have allowed provisions for future plant removal costs in depreciation rates. These plant removal cost recoveries are classified either as AROs or as a regulatory liability for non-ARO obligations. To the extent annual accruals for plant removal costs differ from accruals under approved depreciation rates, a regulatory asset has been established in accordance with the guidance for AROs. (See Note 5. Regulatory Matters.)

Asset Retirement Obligation
 
 
Millions
 
 
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

Accretion Expense
 
3.8

Additional Liabilities Incurred in 2012
 
17.1

Obligation as of December 31, 2012
 

$77.9