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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of changes to asset retirement obligations
The following table shows changes to our AROs during the years ended December 31:
(in millions)
 
2016
 
2015
 
2014
Balance as of January 1
 
$
571.2

 
$
43.6

 
$
42.3

Integrys subsidiaries
 
—

 
491.0

 
—

Accretion
 
28.3

 
14.5

 
2.4

Additions and revisions to estimated cash flows
 
—

 
35.5

*
—

Liabilities settled
 
(41.8
)
 
(13.4
)
 
(1.1
)
Balance as of December 31
 
$
557.7

 
$
571.2

 
$
43.6



*
During 2015, an ARO of $16.1 million was recorded for fly-ash landfills located at generation facilities owned by WE and WPS. An ARO of $9.0 million was also recorded during 2015 for the Hazardous and Solid Waste Management System; Disposal of Coal Combustion Residuals from Electric Utilities rule passed by the EPA in April 2015. In addition, AROs increased $10.4 million in 2015 due to revisions made to estimated cash flows primarily for changes in the weighted average cost to retire natural gas distribution pipe at PGL and NSG.