XML 49 R38.htm IDEA: XBRL DOCUMENT v3.21.2
Asset Retirement Obligations (Tables)
 9 Months Ended
Sep. 30, 2021
Asset Retirement Obligation Disclosure [Abstract]  
Schedule of Changes in Carrying Values of Asset Retirement Obligations The following table reflects changes in the carrying values of asset retirement obligations:

 

 

 

September 30,

2021

 

 

December 31,

2020

 

(Dollars in millions)

 

 

 

 

 

 

 

 

Asset retirement obligation at beginning of year

 

$

19.8

 

 

$

20.7

 

Accretion expense

 

 

0.7

 

 

 

1.1

 

Revision in estimated cash flows

 

 

(2.8

)

 

 

4.6

 

Cash expenditures

 

 

(6.7

)

 

 

(6.6

)

Balance at end of period

 

$

11.0

 

 

$

19.8