Shareholders' Equity (Share Repurchased Under Share Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended	12 Months Ended
	Nov. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Aggregate purchase price		$ 44.7	$ 100.0	$ 434.9
Treasury Stock, Shares, Retired	18.0
Stock Repurchase Program Board Authorized Repurchases [Member]
Class of Stock [Line Items]
Shares repurchased (in shares)		1.3	2.1	10.1
Aggregate purchase price		$ 44.7	$ 100.0	$ 434.9
Average purchase price per share (in dollars per share)		$ 35.51	$ 47.58	$ 42.99
Remaining amount available for share repurchase		$ 219.0