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ASSET RETIREMENT OBLIGATIONS (Tables)
 12 Months Ended
Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of changes to asset retirement obligations
The following table shows changes to our asset retirement obligations through December 31, 2014:
(Millions)
 
Utilities
 
PDI
 
Total
Asset retirement obligations at December 31, 2011
 
$
395.8

 
$
0.5

 
$
396.3

Accretion
 
20.3

 
0.1

 
20.4

Additions and revisions to estimated cash flows
 
(2.3
)
 
1.6

 
(0.7
)
Settlements
 
(5.4
)
 
—

 
(5.4
)
Asset retirement obligations at December 31, 2012
 
408.4

 
2.2

 
410.6

Accretion
 
20.8

 
0.1

 
20.9

Additions and revisions to estimated cash flows
 
70.1

*
0.5

 
70.6

Settlements
 
(11.1
)
 
—

 
(11.1
)
Asset retirement obligations at December 31, 2013
 
488.2

 
2.8

 
491.0

Accretion
 
24.5

 
0.1

 
24.6

Additions and revisions to estimated cash flows
 
(18.3
)
*
0.7

 
(17.6
)
Settlements
 
(17.8
)
 
—

 
(17.8
)
Asset retirement obligations at December 31, 2014
 
$
476.6

 
$
3.6

 
$
480.2


*
Revisions were made to estimated cash flows related to asset retirement obligations primarily due to changes in the weighted average cost to retire natural gas distribution pipe at PGL.