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Asset Retirement Obligations (Tables)
12 Months Ended
Dec. 31, 2020
Asset Retirement Obligation [Abstract]  
Reconciliation of changes in the asset retirement obligation
The following table provides a reconciliation of changes in the asset retirement obligation from operations during each period:
Years ended December 31,
20202019
Asset retirement obligation at beginning of year$15.3 $14.6 
Liabilities settled(0.1)(1.2)
Accretion expense(1)
1.1 1.0 
Revisions in estimated cash flows(2)
(4.9)0.9 
Asset retirement obligation at end of year(3)
$11.4 $15.3 
(1)Included in cost of products sold and operating expenses on the Consolidated Statements of Operations.
(2)Revisions of estimated cash flows in 2020 were primarily due to the identification of more cost efficient demolition methods as well as the timing of projected spending on certain obligations.
(3)The current portion of asset retirement obligation liabilities, which totaled zero and $0.9 million at December 31, 2020 and December 31, 2019, respectively, is classified in accrued liabilities on the Consolidated Balance Sheets.