Investments Measured at Fair Value on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions | Sep. 30, 2015 | Dec. 31, 2014 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | $ 2,307 | $ 1,075 |
Marketable securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 2,248 | 992 |
Marketable securities | U.S. government and agency debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 329 | 321 |
Marketable securities | Mortgage and asset-backed debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 77 | 89 |
Marketable securities | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 1,388 | 534 |
Marketable securities | Other debt and equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 454 | 48 |
Other Long-term Investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 59 | 83 |
Fair Value, Inputs, Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 348 | 340 |
Fair Value, Inputs, Level 1 | Marketable securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 329 | 321 |
Fair Value, Inputs, Level 1 | Marketable securities | U.S. government and agency debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 329 | 321 |
Fair Value, Inputs, Level 1 | Marketable securities | Mortgage and asset-backed debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 1 | Marketable securities | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 1 | Marketable securities | Other debt and equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 1 | Other Long-term Investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 19 | 19 |
Fair Value, Inputs, Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 1,919 | 671 |
Fair Value, Inputs, Level 2 | Marketable securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 1,919 | 671 |
Fair Value, Inputs, Level 2 | Marketable securities | U.S. government and agency debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 2 | Marketable securities | Mortgage and asset-backed debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 77 | 89 |
Fair Value, Inputs, Level 2 | Marketable securities | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 1,388 | 534 |
Fair Value, Inputs, Level 2 | Marketable securities | Other debt and equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 454 | 48 |
Fair Value, Inputs, Level 2 | Other Long-term Investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 3 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 40 | 64 |
Fair Value, Inputs, Level 3 | Marketable securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 3 | Marketable securities | U.S. government and agency debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 3 | Marketable securities | Mortgage and asset-backed debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 3 | Marketable securities | Corporate debt securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 3 | Marketable securities | Other debt and equity securities | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | 0 | 0 |
Fair Value, Inputs, Level 3 | Other Long-term Investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Investments | $ 40 | $ 64 |