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Asset Retirement Obligations | 12 Months Ended
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Dec. 31, 2023
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligations | Asset Retirement Obligations Reconciliations of the Company’s asset retirement obligations are as follows:
| December 31,
| 2023 |  | 2022
| (Dollars in millions)
Balance at beginning of period | $ | 750.0 |  |  | $ | 719.8 |
Liabilities settled | (60.4) |  |  | (51.7) |
Accretion expense | 61.3 |  |  | 56.2 |
Revisions to estimates | (48.1) |  |  | 25.7 |
Balance at end of period | $ | 702.8 |  |  | $ | 750.0 |
Less: Current portion (included in “Accounts payable and accrued expenses”) | 54.2 |  |  | 84.2 |
Noncurrent obligation (included in “Asset retirement obligations, less current portion”) | $ | 648.6 |  |  | $ | 665.8 |
Balance at end of period — active locations | $ | 541.3 |  |  | $ | 557.9 |
Balance at end of period — closed or inactive locations | $ | 161.5 |  |  | $ | 192.1 |
The Company’s reclamation obligations are secured by surety bonds, which are supported by standby letters of credit and restricted cash, and various other forms of collateral. See Note 20. “Financial Instruments, Guarantees With Off-Balance-Sheet Risk and Other Guarantees” for a discussion of the collateral securing the asset retirement obligations.

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- Definition The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481850/410-20-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org//410-20/tableOfContent Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -SubTopic 20 -Topic 410 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481850/410-20-50-2 + Details
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