XML 61 R40.htm IDEA: XBRL DOCUMENT v3.6.0.2

ASSET RETIREMENT OBLIGATION: (Tables)

12 Months Ended

Dec. 31, 2016

ASSET RETIREMENT OBLIGATION:

Summary of asset retirement obligation activity

        The following table summarizes the asset retirement obligation activity for years ended December 31, 2016 and 2015 (in millions):

		2016			2015
Balance as of January 1		$	190.9		$	116.1
Changes in estimates			—			3.8
Additions			10.5			72.2
Closure payments			(2.0	)		(14.6	)
Accretion expense			17.1			13.4
​	​	​	​	​	​	​	​
Balance as of December 31,		$	216.5		$	190.9
​	​	​	​	​	​	​	​
​	​	​	​	​	​	​	​

X

- References

No definition available.

+ Details

Name:	us-gaap_AssetRetirementObligationDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- 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

Name:	us-gaap_ScheduleOfChangeInAssetRetirementObligationTableTextBlock
Namespace Prefix:	us-gaap_
Data Type:	nonnum:textBlockItemType
Balance Type:	na
Period Type:	duration