Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Inventories Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
LIFO Inventory Related Text	last-in, first-out (“LIFO”)
Replacement costs over stated LIFO value	$ 17.7
Replacement cost under stated LIFO value		$ 7.8
Consigned inventory	1.9	1.0
Effect of LIFO Inventory Liquidation on Income	6.0	(6.3)	$ (3.7)
Inventory Write-down	$ (35.6)	$ 30.6	$ (30.6)