Fair Value Measurement of Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Available-for-sale securities
Available-for-sale Securities, Fair Value	$ 752.0	$ 672.7
Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	752.0	672.7
Total fair value measurement of assets	793.3	718.8
Liabilities
Total fair value measurement of liabilities		33.4
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
Total fair value measurement of assets
Liabilities
Total fair value measurement of liabilities
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	752.0	672.7
Total fair value measurement of assets	793.3	718.8
Liabilities
Total fair value measurement of liabilities		33.4
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
Total fair value measurement of assets
Liabilities
Total fair value measurement of liabilities
Corporate debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	331.4	324.7
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
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	331.4	324.7
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
U.S. government and agency debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	200.4	177.2
U.S. government and agency 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
U.S. government and agency 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	200.4	177.2
U.S. government and agency 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
Municipal Bonds [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value		1.0
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
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
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
Foreign government debt securities [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	2.8	6.8
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
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	2.8	6.8
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
Certificates of deposit [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	90.1	88.5
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
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	90.1	88.5
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
Commercial Paper [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Available-for-sale Securities, Fair Value	127.3	74.5
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
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	127.3	74.5
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
Interest Rate Swap [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Derivatives, current and long-term	24.6	27.8
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
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	24.6	27.8
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
Foreign Exchange Forward Contracts [Member] | Fair Value, Measurements, Recurring [Member]
Available-for-sale securities
Derivatives, current and long-term	16.7	18.3
Liabilities
Derivatives, current and long-term	10.3	25.2
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
Liabilities
Derivatives, current and long-term
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	16.7	18.3
Liabilities
Derivatives, current and long-term	10.3	25.2
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
Liabilities
Derivatives, current and long-term
Cross-currency interest rate swaps [Member] | Fair Value, Measurements, Recurring [Member]
Liabilities
Derivatives, current and long-term		8.2
Cross-currency interest rate swaps [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
Cross-currency interest rate swaps [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 swaps [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