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Asset Retirement Obligations - Additional Information (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended |
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Dec. 31, 2012 Structure | Dec. 31, 2011
Asset Retirement Obligations [Line Items] |  |
Estimated CARO ranges per structure, minimum | $ 1 |
Estimated CARO ranges per structure, maximum | 52 |
Number of structures required to demolish | 132 |
Current liability | $ 75 | $ 76

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- Definition Estimated CARO Ranges Per Structure Maximum + References No definition available. + Details
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- Definition Number of structures required to demolish. + References No definition available. + Details
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- Definition Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement 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/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 143 -Paragraph 3, 10, 22 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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