Debt (Narrative) (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended				12 Months Ended		12 Months Ended		1 Months Ended		0 Months Ended
	Sep. 09, 2011	Dec. 20, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 2.875% Notes Due 2016 [Member]	Dec. 20, 2010 2.875% Notes Due 2016 [Member]	Dec. 31, 2011 4.40% Notes Due 2021 [Member]	Dec. 20, 2010 4.40% Notes Due 2021 [Member]	Oct. 31, 2011 Five-Year Credit Facility Expiring In October 2016 [Member]	Oct. 31, 2011 Five-Year Credit Facility Expiring In June 2012 [Member]	Dec. 15, 2010 Common Stock [Member]	Dec. 15, 2010 Capital In Excess Of Par Value [Member]	Sep. 09, 2011 Retained Earnings [Member]	Dec. 15, 2010 Retained Earnings [Member]	Dec. 15, 2010 Accelerated Share Repurchase Agreement [Member]
Debt Instrument [Line Items]
Senior unsecured notes - aggregate principal amount		$ 750,000,000				$ 250,000,000		$ 500,000,000
Debt instrument interest rate					2.875%		4.40%
Debt instrument maturity date					2016		2021
Net proceeds from offering		740,000,000
Debt offering expenses		6,300,000
Debt issuance discount		3,700,000
ASR agreement with the bank to repurchase outstanding common stock															750,000,000
Shares received upon initial settlement under the ASR transaction															8.1
Cash remitted to bank counterparty upon final settlement under the ASR agreement	58,900,000
Decrease to shareholder's investment											2,000,000	10,200,000	69,100,000	737,800,000
Increase of capital in excess of par value	10,200,000
Line of credit facility, borrowing capacity									600,000,000	400,000,000
Line of credit facility, term, in years									5	5
Line of credit facility, expiration date									October 2016	June 2012
Commercial paper			$ 304,500,000	$ 80,500,000
Weighted-average effective interest rate			$ 0.30%	$ 0.40%