Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Fair Value Measurements (Textuals)
Amount of restricted investments measured at fair value included in the balance of Corporate Debt Securities	$ 1.6		$ 2.7
Amount of restricted investments measured at fair value included in the balance of Money Market Funds	75.1		114.3
Amount of Restricted Investments Measured at Fair Value Included in Balance of Mutual Funds	1.0
Amount Of Restricted Investments Measured At Fair Value Included In Balance Of Government Securities			0.6
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets measured at fair value	0		0
Accrued Liabilities, Fair Value Disclosure	0		0
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	1,854.8		1,441.7
Trading securities:
Trading securities measured at fair value on a recurring basis	10.3		8.1
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0		0
Total assets measured at fair value	1,865.1		1,449.8
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, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets measured at fair value	9.6		2.6
Accrued Liabilities, Fair Value Disclosure	(9.6)		(2.6)
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	945.3		803.1
Trading securities:
Trading securities measured at fair value on a recurring basis	0		0
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0.4		0.4
Total assets measured at fair value	945.7		803.5
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, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets measured at fair value	0		0
Accrued Liabilities, Fair Value Disclosure	0		0
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0
Trading securities:
Trading securities measured at fair value on a recurring basis	0		0
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0		0
Total assets measured at fair value	0		0
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, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets measured at fair value	9.6		2.6
Accrued Liabilities, Fair Value Disclosure	(9.6)		(2.6)
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	2,800.1		2,244.8
Trading securities:
Trading securities measured at fair value on a recurring basis	10.3		8.1
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0.4		0.4
Total assets measured at fair value	2,810.8		2,253.3
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, Measurements, Recurring [Member]
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0		0
Derivative liability measured at fair value on a recurring basis	0		0
Foreign Exchange Contract [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets measured at fair value	9.6		2.6
Accrued Liabilities, Fair Value Disclosure	(9.6)		(2.6)
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0.4		0.4
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, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets measured at fair value	0
Accrued Liabilities, Fair Value Disclosure	0
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0		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, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Prepaid expenses and other current assets measured at fair value	9.6		2.6
Accrued Liabilities, Fair Value Disclosure	(9.6)		(2.6)
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0.4		0.4
Derivative liability measured at fair value on a recurring basis	(9.6)		(2.6)
Mutual Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Trading securities:
Trading securities measured at fair value on a recurring basis	10.3	[1]	8.1
Mutual Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Trading securities:
Trading securities measured at fair value on a recurring basis	0	[1]	0
Mutual Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Trading securities:
Trading securities measured at fair value on a recurring basis	0	[1]	0
Mutual Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Trading securities:
Trading securities measured at fair value on a recurring basis	10.3	[1]	8.1
Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	1,854.8		1,441.7
Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	945.3		803.1
Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0
Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	2,800.1		2,244.8
US Government Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	149.3		54.9	[2]
US Government Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	151.7		180.8	[2]
US Government Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0	[2]
US Government Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	301.0		235.7	[2]
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	314.2		208.9
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	116.8		10.1
US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0
US Government-sponsored Enterprises Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	431.0		219.0
Foreign Government Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis			21.0
Foreign Government Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis			26.0
Foreign Government Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis			0
Foreign Government Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis			47.0
Commercial Paper [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0
Commercial Paper [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	10.0		13.5
Commercial Paper [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0
Commercial Paper [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	10.0		13.5
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0	[3]	2.7	[4]
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	510.3	[3]	461.7	[4]
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0	[3]	0	[4]
Corporate Debt Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	510.3	[3]	464.4	[4]
Certificates of Deposit [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0
Certificates of Deposit [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	31.8		21.0
Certificates of Deposit [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0
Certificates of Deposit [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	31.8		21.0
Asset-backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0
Asset-backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	124.7		90.0
Asset-backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0		0
Asset-backed Securities [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	124.7		90.0
Money Market Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	1,391.3	[5]	1,154.2	[6]
Money Market Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0	[5]	0	[6]
Money Market Funds [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	0	[5]	0	[6]
Money Market Funds [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities:
Available-for-sale securities measured at fair value on a recurring basis	$ 1,391.3	[5]	$ 1,154.2	[6]

[1] Balance includes $9.3 million of the Company's non-qualified deferred compensation plan assets and $1.0 million of restricted investments measured at fair market value, related to the Company's India Gratuity Trust.

[2] Balance includes $0.6 million of restricted investments measured at fair market value, related to an acquisition completed in 2005. For additional information regarding the Company's restricted investments, see Note 4, Cash, Cash Equivalents, and Investments, under the heading “Restricted Cash and Investments.” Restricted investments are included in the restricted cash balance in the consolidated balance sheet.

[3] Balance includes $1.6 million of restricted investments measured at fair market value, related to the Company's India Gratuity Trust.

[4] Balance includes $2.7 million of restricted investments measured at fair market value, related to the Company's India Gratuity Trust.

[5] Balance includes $75.1 million of restricted investments measured at fair market value, related to the Company's D&O trust and acquisition related escrows.

[6] Balance includes $114.3 million of restricted investments measured at fair market value, related to the Company's D&O trust and acquisition related escrows.