Fair Value Measurement (Tables)

6 Months Ended

Jun. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of Carrying Amount and Estimated Fair Values

The following presents the carrying amounts and estimated fair values of financial instruments not measured at fair value in the Condensed Consolidated Balance Sheets at June 30, 2018 and December 31, 2017: 

	June 30, 2018 (unaudited)				December 31, 2017
(millions)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Long-term borrowings
Restated Credit Facility, net of original discount on borrowings and deferred financing costs	$	123.8	$	123.8	$	151.0	$	151.0
Other obligations	$	2.6	$	2.6	$	2.8	$	2.8