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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2013
Asset Retirement Obligation Disclosure [Abstract] |
Schedule of changes in asset retirement obligations | Changes in asset retirement obligations for the years ended December 31, 2013 and 2012 were as follows:
(in millions) |  | 2013 |  | 2012
Balance at beginning of year |  | $ | 13.0 |  |  | $ | 12.8 |
Accretion expense |  | 1.1 |  |  | 1.1 |
Payments |  | (0.8 | ) |  | (0.6 | )
Revision of estimates |  | 13.8 |  |  | (0.3 | )
Liabilities incurred |  | 0.6 |  |  | — |
Balance at end of year |  | $ | 27.7 |  |  | $ | 13.0 |

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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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