Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2013 Notes Payable 4.5 Percent Due 2021 [Member]	Dec. 31, 2012 Notes Payable 4.5 Percent Due 2021 [Member]	Mar. 31, 2013 Derivatives not designated as hedging instruments Forward exchange contracts	Dec. 31, 2012 Derivatives not designated as hedging instruments Forward exchange contracts	Dec. 31, 2012 Designated as Hedging Instrument [Member] Interest-rate swap	Mar. 31, 2013 (Level 2) Measured on a recurring basis Interest-rate swap	Dec. 31, 2012 (Level 2) Measured on a recurring basis Interest-rate swap
Derivative Instruments
Maximum Remaining Maturity of Foreign Currency Derivatives	6 months
Derivative net asset (liability) position							$ 12.8	$ 17.0
Notional amounts of derivatives				7.3	6.1	400.0
Number of swap agreements						4
Debt instrument, face amount		$ 400
Fixed-rate (as a percent)			4.50%