Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2014

Asset Retirement Obligations [Abstract]

Changes in Aggregate Asset Retirement Obligations

Our asset retirement obligations primarily relate to certain gas gathering pipelines and processing facilities, and are included in our consolidated balance sheets as a component of other long-term liabilities. The changes in our aggregate asset retirement obligations are as follows:

	Three Months Ended
	March 31, 2014
Beginning of period	$	50.9
Change in cash flow estimate		2.1
Accretion expense		1.2
End of period	$	54.2