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Asset Retirement Obligations

12 Months Ended

Dec. 31, 2011

Asset Retirement Obligation [Abstract]

The following table presents the change in our AROs during 2011 and 2010:



	2011			2010
	(Millions of Dollars)

Balance as of January 1	$	52.6		$	57.9
Liabilities Incurred	0.6			—
Liabilities Settled	(2.2		)	(2.5		)
Accretion	3.0			3.1
Cash Flow Revisions	1.5			(5.9		)
Balance as of December 31	$	55.5		$	52.6

- Definition

The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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