SHORT-TERM BORROWINGS AND LONG-TERM DEBT (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2011
Long-Term Debt
Principal value of long-term debt obligations	$ 1,500.0	$ 1,500.0
Unamortized basis adjustment for terminated interest rate swaps	32.9	35.3
Unamortized bond discount	(3.2)	(3.4)
Long-term debt	1,529.7	1,531.9
Long-term debt - estimated fair value	1,636.8
Interest expense	16.2	14.4
Interest income	1.7	1.3
3.50% Notes due 2014
Long-Term Debt
Stated rate (as a percent)	3.50%	3.50%
Principal value of long-term debt obligations	500.0	500.0
4.90% Notes due 2019
Long-Term Debt
Stated rate (as a percent)	4.90%	4.90%
Principal value of long-term debt obligations	700.0	700.0
5.90% Notes due 2039
Long-Term Debt
Stated rate (as a percent)	5.90%	5.90%
Principal value of long-term debt obligations	$ 300.0	$ 300.0