Shareholders' Equity (Shares Repurchased Under Share Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Class of Stock [Line Items]
Aggregate purchase price		$ 11.2	$ 33.5		$ 73.4	$ 26.6
Stock Repurchase Program Board Authorized Repurchases [Member]
Class of Stock [Line Items]
Shares repurchased (in shares)	0.0			0.0			1.3	2.1
Aggregate purchase price	$ 0.0			$ 0.0			$ 44.7	$ 100.0
Average purchase price per share (in dollars per share)	$ 0			$ 0			$ 35.51	$ 47.58
Remaining amount available for share repurchase	$ 219.0						$ 219.0