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ASSET RETIREMENT OBLIGATION: (Tables)

6 Months Ended

Jun. 30, 2025

ASSET RETIREMENT OBLIGATION:

Summary of asset retirement obligation activity

The following table summarizes the asset retirement obligation activity for the six-month periods ended June 30, 2025 and 2024 (in millions):

​	​	​	​	​	​	​
​		2025			2024
Balance as of January 1	​	$	546.1	​	$	612.6
Changes in estimates	​		(48.5)	​		(7.7)
Closure payments	​		—	​		—
Accretion expense	​		12.2	​		14.3
Balance as of June 30,	​	$	509.9	​	$	619.2

​

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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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