Business Segments - Segment Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting [Abstract]
Primary	$ 1,480.7	$ 1,531.0	$ 1,493.0
Corporate, unallocated	56.8	50.6	47.3
TOTAL	$ 1,537.5	$ 1,581.6	$ 1,540.3