Asset Retirement Obligations (Tables)

12 Months Ended

Dec. 31, 2017

Asset Retirement Obligation Disclosure [Abstract]

Schedule of changes in asset retirement obligations

Changes in asset retirement obligations for the years ended December 31, 2017 and 2016 were as follows:

(In millions)	2017			2016
Balance at beginning of year	$	23.3		$	25.0
Accretion expense	0.8			0.7
Payments	(0.7		)	(2.0		)
Revision of estimates	0.1			(0.4		)
Balance at end of year	$	23.5		$	23.3