Fair Value Measurements of Assets and Liabilities - Fair Value Measurements of Assets and Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	$ 466.5	$ 868.9
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	466.5	868.9
Total fair value measurement of assets	615.2	1,018.4
Total fair value measurement of liabilities		61.0
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	372.2	516.5
Fair Value, Measurements, Recurring [Member] | U.S. Government and Agency Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	66.9	194.3
Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	11.5	57.8
Fair Value, Measurements, Recurring [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	15.9	100.3
Fair Value, Measurements, Recurring [Member] | Foreign Exchange Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, current and long-term	114.7	125.5
Derivatives, current and long-term	1.8	1.7
Fair Value, Measurements, Recurring [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, current and long-term	34.0	24.0
Fair Value, Measurements, Recurring [Member] | Forward Starting Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, current and long-term		59.3
Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	466.5	868.9
Total fair value measurement of assets	615.2	1,018.4
Total fair value measurement of liabilities		61.0
Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	372.2	516.5
Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | U.S. Government and Agency Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	66.9	194.3
Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	11.5	57.8
Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities, Fair Value	15.9	100.3
Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Exchange Forward Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, current and long-term	114.7	125.5
Derivatives, current and long-term	1.8	1.7
Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, current and long-term	$ 34.0	24.0
Fair Value Measurements at Reporting Date Using: Significant Other Observable Inputs (Level 2) [Member] | Fair Value, Measurements, Recurring [Member] | Forward Starting Interest Rate Swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, current and long-term		$ 59.3