Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2012

Asset Retirement Obligations [Abstract]

Asset retirement obligations roll forward

Changes in ARO were as follows:

	Asset Retirement Obligations
	2012			2011
	(in millions)
ARO liability at January 1,	$	163.9		$	148.3
Accretion		2.5			2.3
Liabilities incurred		1.6			2.0
Liabilities settled		(0.3	)		(0.2	)
ARO liability at March 31,	$	167.7		$	152.4