Shareholders' Equity (Shares Repurchased Under Share Repurchase Program) (Details) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Aug. 31, 2017
Class of Stock [Line Items]
Aggregate purchase price			$ 436,000,000
Stock Repurchase Program Board Authorized Repurchases [Member]
Class of Stock [Line Items]
Additional board authorized share repurchases					$ 250,000,000
Shares repurchased (in shares)	9.2	1.0	10.1	9.9
Aggregate purchase price	$ 400,000,000	$ 50,000,000	$ 434,900,000	$ 470,600,000
Average purchase price per share (in dollars per share)	$ 43.28	$ 48.62	$ 42.99	$ 47.48
Remaining amount available for share repurchase	$ 113,700,000		$ 113,700,000