Debt (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended						12 Months Ended			12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 4.625% Senior Notes due November 30, 2019 [Member]	Dec. 31, 2010 4.625% Senior Notes due November 30, 2019 [Member]	Nov. 30, 2009 4.625% Senior Notes due November 30, 2019 [Member]	Dec. 31, 2011 5.75% Senior Notes due November 30, 2039 [Member]	Dec. 31, 2010 5.75% Senior Notes due November 30, 2039 [Member]	Nov. 30, 2009 5.75% Senior Notes due November 30, 2039 [Member]	Dec. 31, 2011 1.4% Senior Notes due November 30, 2014 [Member]	Nov. 30, 2011 1.4% Senior Notes due November 30, 2014 [Member]	Dec. 31, 2010 1.4% Senior Notes due November 30, 2014 [Member]	Dec. 31, 2011 3.375% Senior Notes due November 30, 2021 [Member]	Nov. 30, 2011 3.375% Senior Notes due November 30, 2021 [Member]	Dec. 31, 2010 3.375% Senior Notes due November 30, 2021 [Member]
Debt Instrument [Line Items]
Aggregate Principal amount of Senior Notes				$ 500.0	$ 500.0	$ 500.0	$ 500.0	$ 500.0	$ 500.0	$ 250.0	$ 250.0	$ 0	$ 300.0	$ 300.0	$ 0
Interest rate of Senior Notes		4.625%				4.625%			5.75%		1.40%			3.375%
Effective interest rate of Senior Notes				4.634%			5.762%			1.424%			3.396%
Debt instrument, basis spread added to base reference				0.20%			0.25%			0.15%
Debt (Textual)
Proceeds from issuance of notes	549.3		998.8
Percentage of amount of the senior notes being redeemed	100.00%
Estimated fair value of Senior Notes	1,693.0	1,022.0
Debt instrument original discount	0.7		1.2
Debt instruments redemption terms	redemption price equal to the greater of 1) 100 percent of the principal amount of the notes being redeemed; or 2) the sum of the present values of the remaining scheduled payments of principal and interest (not including any portion of such payments of interest accrued as of the date of redemption), discounted to the date of redemption on a semi-annual basis at the Treasury Rate (as defined in the debt agreement), plus 20 basis points, in the case of the 2019 notes, and 25 basis points, in the case of the 2039 notes
Available borrowings under Senior Credit Facility, Increased by provisions, Net	1,350
Available borrowings under Senior Credit Facility, Increased by provisions, Net	1,207.0
Maximum Leverage Ratio	300.00%
Minimum Interest Coverage Ratio	350.00%
Available uncommitted credit facilities, Net	63.6
Weighted average interest rate for all borrowings, short-term debt	0.10%
Weighted average interest rate for all borrowings, long-term debt	3.80%
Interest paid on Debt	$ 55.0	$ 59.8	$ 17.0