Fair Value Measurements, Assets by Balance Sheet Grouping (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents measured at fair value	$ 1,316.2	$ 1,039.9
Short-term investments measured at fair value	168.9	150.7
Long-term investments measured at fair value	303.9	142.2
Restricted cash and investments measured at fair value	76.1	117.0
Prepaid expenses and other current assets measured at fair value	0	0
Total assets measured at fair value	1,865.1	1,449.8
Accrued Liabilities, Fair Value Disclosure	0	0
Derivative liability measured at fair value on a recurring basis	0	0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents measured at fair value	34.5	85.7
Short-term investments measured at fair value	472.4	323.8
Long-term investments measured at fair value	436.8	393.0
Restricted cash and investments measured at fair value	1.6	0.6
Prepaid expenses and other current assets measured at fair value	0.4	0.4
Total assets measured at fair value	945.7	803.5
Accrued Liabilities, Fair Value Disclosure	(9.6)	(2.6)
Derivative liability measured at fair value on a recurring basis	(9.6)	(2.6)
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents measured at fair value	0	0
Short-term investments measured at fair value	0	0
Long-term investments measured at fair value	0	0
Restricted cash and investments measured at fair value	0	0
Prepaid expenses and other current assets measured at fair value	0	0
Total assets measured at fair value	0	0
Accrued Liabilities, Fair Value Disclosure	0	0
Derivative liability measured at fair value on a recurring basis	0	0
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents measured at fair value	1,350.7	1,125.6
Short-term investments measured at fair value	641.3	474.5
Long-term investments measured at fair value	740.7	535.2
Restricted cash and investments measured at fair value	77.7	117.6
Prepaid expenses and other current assets measured at fair value	0.4	0.4
Total assets measured at fair value	2,810.8	2,253.3
Accrued Liabilities, Fair Value Disclosure	(9.6)	(2.6)
Derivative liability measured at fair value on a recurring basis	(9.6)	(2.6)
Foreign Exchange Contract [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability measured at fair value on a recurring basis	0	0
Foreign Exchange Contract [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued Liabilities, Fair Value Disclosure	(9.6)	(2.6)
Derivative liability measured at fair value on a recurring basis	(9.6)	(2.6)
Foreign Exchange Contract [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued Liabilities, Fair Value Disclosure	0
Derivative liability measured at fair value on a recurring basis	0	0
Foreign Exchange Contract [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accrued Liabilities, Fair Value Disclosure	(9.6)	(2.6)
Derivative liability measured at fair value on a recurring basis	$ (9.6)	$ (2.6)