Summary of Significant Accounting Policies (Activity in the LIFO Reserve) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) operation	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2020 USD ($)
LIFO Reserve [Roll Forward]
Balance, beginning of year	$ 49.9	$ 82.2	$ 50.9
LIFO expense (benefit)	8.1	(32.3)	31.3
Allocated to divested businesses	(2.8)	0.0	0.0
Balance, end of year	$ 49.9	$ 82.2	$ 50.9	$ 55.2
Number of disposals | operation	2