Fair Value Measurements, Assets by Balance Sheet Grouping (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
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
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	1,174.4	1,125.6
Short-term investments measured at fair value	632.4	474.5
Long-term investments measured at fair value	775.5	535.2
Restricted cash and investments measured at fair value	90.0	117.6
Prepaid expenses and other current assets measured at fair value	0.7	0.4
Total assets measured at fair value	2,673.0	2,253.3
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	1,174.4	1,039.9
Short-term investments measured at fair value	140.9	150.7
Long-term investments measured at fair value	288.2	142.2
Restricted cash and investments measured at fair value	88.2	117.0
Prepaid expenses and other current assets measured at fair value	0	0
Total assets measured at fair value	1,691.7	1,449.8
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	0	85.7
Short-term investments measured at fair value	491.5	323.8
Long-term investments measured at fair value	487.3	393.0
Restricted cash and investments measured at fair value	1.8	0.6
Prepaid expenses and other current assets measured at fair value	0.7	0.4
Total assets measured at fair value	$ 981.3	$ 803.5

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

+ References+ Details