Business Segment (Summary of Information by Business Segment) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total Assets	$ 2,583.4		$ 2,687.2
External revenues	3,184.8	$ 3,116.4
Income (Loss)	89.3	5.3
Operating Segments | Marketing
Segment Reporting Information [Line Items]
Total Assets	2,282.0
External revenues	3,184.7	3,116.3
Income (Loss)	100.9	16.2
Corporate and other assets
Segment Reporting Information [Line Items]
Total Assets	301.4
External revenues	0.1	0.1
Income (Loss)	$ (11.6)	$ (10.9)