Asset Retirement Obligation (Notes)

6 Months Ended

Jun. 30, 2014

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations

(9)Asset Retirement Obligations

The schedule below summarizes the changes in the Company’s asset retirement obligations:

	June 30, 2014		June 30, 2013
	(in millions)
Beginning asset retirement obligations	$	7.7	$	9.1
Revisions to existing liabilities	2.2		0.4
Liabilities acquired	0.5		—
Accretion	0.3		0.2
Ending asset retirement obligations	$	10.7	$	9.7