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ASSET RETIREMENT OBLIGATION: (Tables)

6 Months Ended

Jun. 30, 2016

ASSET RETIREMENT OBLIGATION:

Summary of asset retirement obligation activity

The following table summarizes the asset retirement obligation activity for the six months ended June 30, 2016 and 2015 ($ in millions):

		2016			2015
Balance as of January 1		$	190.9		$	116.1
Changes in estimates		—			—
Payments		(1.4		)	(8.2		)
Accretion expense		13.9			5.2
Balance as of June 30		$	203.4		$	113.1

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- References

No definition available.

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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

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