Asset Retirement Obligations (Tables)

6 Months Ended

Jun. 30, 2020

Asset Retirement Obligation [Abstract]

Asset Retirement Obligation Disclosure [Text Block]

	Asset Retirement Obligations
	June 30,		December 31,
	2020		2019
Balance Sheet line item	(in millions)
Current:
Asset retirement obligations, current liability	$	6.2	$	6.0
Long-term:
Asset retirement obligations	94.9		94.9
Total ARO Liability	$	101.1	$	100.9

Schedule of Change in Asset Retirement Obligation [Table Text Block]

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

	Asset Retirement Obligations
	(in millions)
ARO liability at January 1, 2020	$	100.9
Accretion	1.9
Additions	1.0
Revisions	(0.5)
Liabilities related to assets sold	(1.3)
Liabilities settled	(0.9)
ARO liability at June 30, 2020	$	101.1