Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2018

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
	2018
	(in millions)
ARO liability at January 1,	$	214.1
Accretion	1.7
Additions	1.5
Revisions	(3.4		)
Liabilities related to assets sold	(3.4		)
ARO liability at March 31,	$	210.5