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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2016
Asset Retirement Obligation Disclosure [Abstract] |
Reconciliations of the Company's ARO liability | Reconciliations of the Company’s asset retirement obligations are as follows:
| December 31,
| 2016 |  | 2015
| (Dollars in millions)
Balance at beginning of year | $ | 712.1 |  |  | $ | 752.5 |
Liabilities incurred or acquired | — |  |  | 1.3 |
Liabilities settled or disposed | (41.5 | ) |  | (53.3 | )
Accretion expense | 45.7 |  |  | 42.7 |
Revisions to estimates | 42.5 |  |  | (31.1 | )
Balance at end of year | $ | 758.8 |  |  | $ | 712.1 |
Less: Current portion (included in "Accounts payable and accrued expenses") | 41.0 |  |  | 25.5 |
Noncurrent obligation (included in "Asset retirement obligations") | $ | 717.8 |  |  | $ | 686.6 |
Balance at end of year — active locations | $ | 651.1 |  |  | $ | 656.8 |
Balance at end of year — closed or inactive locations | $ | 107.7 |  |  | $ | 55.3 |

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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859 + Details
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