Asset Retirement Obligations (Tables)

9 Months Ended

Sep. 30, 2016

Asset Retirement Obligation [Abstract]

Asset retirement obligations rollforward [Table Text Block]

The following is a reconciliation of the changes in the Company's ARO for the period specified below:

	Asset Retirement Obligations
	2016
	(in millions)
ARO liability at January 1,	$	206.8
Accretion	6.5
Additions	3.6
Revisions	7.1
Liabilities settled	(6.5		)
ARO liability at September 30,	$	217.5