Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2017

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
	2017
	(in millions)
ARO liability at January 1,	$	231.6
Accretion	2.1
Additions	1.8
Revisions	0.2
Liabilities settled	(1.6		)
ARO liability at March 31,	$	234.1