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Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2019
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of changes in asset retirement obligations
Changes in asset retirement obligations for the years ended December 31, 2019 and 2018 were as follows:
(In millions)
 
2019
 
2018
Balance at beginning of year
 
$
23.1

 
$
23.5

Accretion expense
 
0.9

 
0.8

Payments
 
(0.3
)
 
(1.2
)
Balance at end of year
 
$
23.7

 
$
23.1