Fair Value Measurements (Details) (USD $) In Millions	Sep. 30, 2011		Dec. 31, 2010
Fair Value Measurements (Textuals)
Amount of restricted investments measured at fair value included in the balance of Government Securities			$ 0.6
Amount of restricted investments measured at fair value included in the balance of Corporate Debt Securities	1.8		2.7
Amount of restricted investments measured at fair value included in the balance of Money Market Funds	87.0		114.3
Amount of Restricted Investments Measured at Fair Value Included in Balance of Mutual Funds	1.2
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	2,661.0		2,244.8
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	1,680.4		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	980.6		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
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	361.5		235.7	[1]
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	144.8		54.9	[1]
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	216.7		180.8	[1]
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	[1]
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	368.4		219.0
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	274.2		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	94.2		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
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	2.4		47.0
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	0		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	2.4		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		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			13.5
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
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			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
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	517.4	[2]	464.4	[3]
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	[2]	2.7	[3]
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	517.4	[2]	461.7	[3]
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	[2]	0	[3]
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	38.0		21.0
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	38.0		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
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	111.9		90.0
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	111.9		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
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	1,261.4	[4]	1,154.2	[5]
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	1,261.4	[4]	1,154.2	[5]
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	[4]	0	[5]
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	[4]	0	[5]
Fair Value, Inputs, Level 3 [Member] | Mutual Funds [Member] | Fair Value, Measurements, Recurring [Member]
Trading securities:
Trading securities measured at fair value on a recurring basis	0	[6]	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	11.3	[6]	8.1
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	11.3	[6]	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	[6]	0
Fair Value, Inputs, Level 3 [Member] | Foreign Exchange Contract [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Derivative assets 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]
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0.7		0.4
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
Foreign Exchange Contract [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0.7		0.4
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	2,661.0		2,244.8
Trading securities:
Trading securities measured at fair value on a recurring basis	11.3		8.1
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0.7		0.4
Total assets measured at fair value	2,673.0		2,253.3
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	1,680.4		1,441.7
Trading securities:
Trading securities measured at fair value on a recurring basis	11.3		8.1
Derivative assets:
Derivative assets measured at fair value on a recurring basis	0		0
Total assets measured at fair value	1,691.7		1,449.8
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	980.6		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	0.7		0.4
Total assets measured at fair value	981.3		803.5
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
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

[1] 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 5, Cash, Cash Equivalents, and Investments, under the heading “Restricted Cash.” Restricted investments are included in the restricted cash balance in the condensed consolidated balance sheet.

[2] Balance includes $1.8 million of restricted investments measured at fair market value, related to the Company's India Gratuity Trust.

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

[4] Balance includes $87.0 million of restricted investments measured at fair market value, related to the Company's D&O trust and acquisition related escrows.

[5] 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.

[6] Balance includes $1.2 million of restricted investments measured at fair market value, related to the Company's India Gratuity Trust.