Fair Value Measurement (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of carrying and estimated fair values of the Company's financial instruments

The following table presents the carrying amounts and estimated fair values of financial instruments not measured at fair value in the Consolidated Balance Sheets at December 31, 2018 and 2017:

	2018				2017
(millions)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term borrowings
Credit Facility, net of original discount on borrowings and deferred financing costs	$	371.2	$	371.2	$	151.0	$	151.0
Other obligations	$	15.4	$	15.4	$	2.8	$	2.8