Assets Measured at Fair Value on Recurring Basis (Detail) (USD $) | Jun. 30, 2014 | Dec. 31, 2013 |
In Millions, unless otherwise specified |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | $222.50 | $101 |
Investments Including Cash Equivalents And Restricted Cash | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 264.4 | 150.2 |
Cash and Cash Equivalents | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | -41.9 | 49.2 |
Short-term investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 194.7 | 145.8 |
Short-term investments | Cash and money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 30.6 | 34.9 |
Short-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 11.5 | 11 |
Short-term investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 15.5 | 5 |
Short-term investments | Securities of government-sponsored entities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 5 | 7.5 |
Short-term investments | Corporate debt securities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 132.1 | 87.4 |
Long-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 9.2 | 4.4 |
Long-term investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Carrying Value | 60.5 | ' |
Quoted Prices in Active Markets for Identical Assets (Level 1) | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 16.2 | 11 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Investments Including Cash Equivalents And Restricted Cash | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 51.3 | 50.3 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and Cash Equivalents | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | -35.1 | 39.3 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 42.1 | 45.9 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Cash and money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 30.6 | 34.9 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 11.5 | 11 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Securities of government-sponsored entities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments | Corporate debt securities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 9.2 | 4.4 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | ' |
Significant Other Observable Inputs (Level 2) | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 206.3 | 90 |
Significant Other Observable Inputs (Level 2) | Investments Including Cash Equivalents And Restricted Cash | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 213.1 | 99.9 |
Significant Other Observable Inputs (Level 2) | Cash and Cash Equivalents | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | -6.8 | 9.9 |
Significant Other Observable Inputs (Level 2) | Short-term investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 152.6 | 99.9 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Cash and money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 15.5 | 5 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Securities of government-sponsored entities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 5 | 7.5 |
Significant Other Observable Inputs (Level 2) | Short-term investments | Corporate debt securities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 132.1 | 87.4 |
Significant Other Observable Inputs (Level 2) | Long-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Other Observable Inputs (Level 2) | Long-term investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 60.5 | ' |
Significant Unobservable Inputs (Level 3) | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Investments Including Cash Equivalents And Restricted Cash | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Cash and Cash Equivalents | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Cash and money market funds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Commercial paper | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Securities of government-sponsored entities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Short-term investments | Corporate debt securities | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Long-term investments | Certificates of deposit | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | 0 | 0 |
Significant Unobservable Inputs (Level 3) | Long-term investments | Corporate bonds | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Fair value of assets on recurring basis | $0 | ' |