Fair Value Measurements of Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Available-for-sale securities
Available-for-sale Securities, Fair Value	$ 672.7	$ 410.6
Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	672.7	410.6
Total fair value measurement of assets	718.8	446.6
Liabilities
Total fair value measurement of liabilities	33.4	40.0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Total fair value measurement of assets	0	0
Liabilities
Total fair value measurement of liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	672.7	410.6
Total fair value measurement of assets	718.8	446.6
Liabilities
Total fair value measurement of liabilities	33.4	40.0
Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Total fair value measurement of assets	0	0
Liabilities
Total fair value measurement of liabilities	0	0
Corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	324.7	203.8
Corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	324.7	203.8
Corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
U.S. Government Agencies and Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	177.2	47.9
U.S. Government Agencies and Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
U.S. Government Agencies and Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	177.2	47.9
U.S. Government Agencies and Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	1.0	1.1
Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	1.0	1.1
Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Foreign government debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	6.8	10.3
Foreign government debt securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Foreign government debt securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	6.8	10.3
Foreign government debt securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	88.5	131.4
Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	88.5	131.4
Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	74.5	16.1
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	74.5	16.1
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	0	0
Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Derivatives, current and long-term	27.8	1.5
Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Available-for-sale securities
Derivatives, current and long-term	0	0
Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Available-for-sale securities
Derivatives, current and long-term	27.8	1.5
Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Available-for-sale securities
Derivatives, current and long-term	0	0
Foreign Exchange Forward Contracts [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Derivatives, current and long-term	18.3	34.5
Liabilities
Derivatives, current and long-term	25.2	40.0
Foreign Exchange Forward Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Available-for-sale securities
Derivatives, current and long-term	0	0
Liabilities
Derivatives, current and long-term	0	0
Foreign Exchange Forward Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Available-for-sale securities
Derivatives, current and long-term	18.3	34.5
Liabilities
Derivatives, current and long-term	25.2	40.0
Foreign Exchange Forward Contracts [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Available-for-sale securities
Derivatives, current and long-term	0	0
Liabilities
Derivatives, current and long-term	0	0
Cross Currency Interest Rate Contract [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities
Derivatives, current and long-term	8.2
Cross Currency Interest Rate Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Liabilities
Derivatives, current and long-term	0
Cross Currency Interest Rate Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member]
Liabilities
Derivatives, current and long-term	8.2
Cross Currency Interest Rate Contract [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value Measurements at Reporting Date Using: Significant Unobservable Inputs (Level 3) [Member]
Liabilities
Derivatives, current and long-term	$ 0