Shareholders' Equity (Narrative) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				1 Months Ended
	Mar. 31, 2012	Mar. 31, 2012 Treasury Stock [Member]	Mar. 31, 2012 Stock Repurchase Program Board Authorized Repurchases [Member]	Mar. 31, 2011 Stock Repurchase Program Board Authorized Repurchases [Member]	Apr. 24, 2012 Stock Repurchase Program Board Authorized Repurchases [Member] Repurchase of Equity [Member]
Class of Stock [Line Items]
Additional authorized amount for share repurchases under the share repurchase program			$ 250.0
Amount available for share repurchases under the share repurchase program			244.4		173.6
Shares repurchased			11.7	1.8	2.1
Aggregate purchase price	$ 405.7	$ 405.7	$ 405.4	$ 58.8	$ 70.8
Average purchase price per share			$ 34.72	$ 32.84	$ 33.62