Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2021

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligation

The following table summarizes the aggregate carrying amount of the Company's ARO as of December 31, 2021 and 2020 (in millions):

	2021		2020
Balance at beginning of year	$	63.1	$	60.4
Liabilities recorded	9.5		1.3
Liabilities settled	(2.2)		(0.9)
Accretion expense	2.9		2.3
Revision of estimates	(8.4)		—
Balance at end of year	64.9		63.1
Less:  Current portion of ARO	(3.4)		(8.2)
Long-term ARO	$	61.5	$	54.9