Goodwill (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of amounts for goodwill and changes to carrying value by operating segment

The amounts for goodwill and changes to carrying value by reportable segment are as follows:

(millions)	Region One		Region Two		Total
Balance as of December 31, 2015	$	368.6	$	62.7	$	431.3
Foreign currency translation	0.1		—		0.1
Balance as of December 31, 2016	$	368.7	$	62.7	$	431.4
Foreign currency translation	0.3		—		0.3
Balance as of December 31, 2017	$	369.0	$	62.7	$	431.7