Asset Retirement Obligations (Tables)

6 Months Ended

Jun. 30, 2013

Asset Retirement Obligation [Abstract]

Asset retirement obligations roll forward

The following is a reconciliation of the changes in the Company's asset retirement obligation from January 1, 2013, to June 30, 2013:

	Asset Retirement Obligations
	2013
	(in millions)
ARO liability at January 1,	$	193.1
Accretion	7.7
Liabilities incurred	6.9
Revisions	(16.5		)
Liabilities settled	(9.8		)
ARO liability at June 30,	$	181.4