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ASSET RETIREMENT OBLIGATION: (Tables)

12 Months Ended

Dec. 31, 2012

ASSET RETIREMENT OBLIGATION:

Summary of the asset retirement obligation activity

The following table summarizes the asset retirement obligation activity for the two years ended December 31, 2012 and 2011 (in millions):

		2012			2011
Balance as of January 1		$	62.0		$	59.1
Changes in estimates		27.4			—
Additions		25.1			—
Closure payments		(0.3		)	(0.5		)
Accretion expense		4.0			3.4
Balance as of December 31,		$	118.2		$	62.0

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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

-Topic 410

-SubTopic 30

-Publisher FASB

-Number

-Article

-Subparagraph

-Name Accounting Standards Codification

-Paragraph 5

-Section 50

-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13201-110859

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