Shareholders' Equity (Shares Repurchased Under Share Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Class of Stock [Line Items]
Aggregate purchase price		$ 80.0	$ 11.2	$ 33.5
Stock Repurchase Program Board Authorized Repurchases [Member]
Class of Stock [Line Items]
Shares repurchased (in shares)	0.0		0.3		2.5	1.3
Aggregate purchase price	$ 0.0		$ 11.2		$ 80.0	$ 44.7
Average purchase price per share (in dollars per share)	$ 0		$ 39.54		$ 31.95	$ 35.51
Remaining amount available for share repurchase	$ 139.0				$ 139.0