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ASSET RETIREMENT OBLIGATION: (Tables)

3 Months Ended

Mar. 31, 2018

ASSET RETIREMENT OBLIGATION:

Summary of asset retirement obligation activity

The following table summarizes the asset retirement obligation activity for the three months ended March 31, 2018 and 2017 (in millions):

		2018			2017
Balance as of January 1		$	222.5		$	216.5
Changes in estimates		(5.2		)	—
Payments		—			(0.3		)
Accretion expense		3.2			6.1
Balance as of March 31,		$	220.5		$	222.3

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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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