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, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Class of Stock [Line Items]
Aggregate purchase price			$ 35.9
Stock Repurchase Program Board Authorized Repurchases [Member]
Class of Stock [Line Items]
Shares repurchased (in shares)	0.9	1.0	0.9	8.9
Aggregate purchase price	$ 34.9	$ 50.0	$ 34.9	$ 420.6
Average purchase price per share (in dollars per share)	$ 39.92	$ 48.51	$ 39.92	$ 47.35
Remaining amount available for share repurchase	$ 263.7		$ 263.7