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ASSET RETIREMENT OBLIGATIONS (Tables)
 12 Months Ended
Dec. 31, 2019
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)
 
2019
 
2018
 
2017
Balance as of January 1
 
$
50.8

 
$
34.1

 
$
32.6

Accretion
 
2.5

 
1.8

 
1.6

Additions and revisions to estimated cash flows
 
(3.7
)
 
16.6

(2) 
0.4

Liabilities settled
 
(8.1
)
(1) 
(1.7
)
 
(0.5
)
Balance as of December 31
 
$
41.5

 
$
50.8

 
$
34.1


(1) 
AROs decreased $8.1 million in 2019 primarily due to the settlement of AROs for the abatement of asbestos at our generation facilities.

(2) 
AROs increased $10.7 million in 2018 due to revisions made to estimated cash flows for the abatement of asbestos at our Pulliam power plant. A $5.6 million ARO was also recorded during 2018 for the legal requirement to dismantle, at retirement, the wind generation project known as Forward Wind Energy Center. See Note 2, Acquisitions, for more information on Forward Wind Energy Center.