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ASSET RETIREMENT OBLIGATION: (Tables)

6 Months Ended

Jun. 30, 2023

ASSET RETIREMENT OBLIGATION:

Summary of asset retirement obligation activity

​

The following table summarizes the asset retirement obligation activity for the first six months of 2023 and 2022 (in millions):

​	​	​	​	​	​	​
​		2023			2022
Balance as of January 1	​	$	585.3	​	$	562.9
Changes in estimates	​		—	​		43.3
Closure payments	​		(0.3)	​		(3.6)
Accretion expense	​		12.9	​		13.0
Balance as of June 30,	​	$	597.9	​	$	615.6

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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/2009/role/commonPracticeRef
-Topic 410
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481850/410-20-50-1

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