Fair Value Measurement (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	$ 14,165	$ 13,527
Change in fair value of contingent consideration liability	25
U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	5,183	5,948
U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	4,815	4,475
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	4,167	3,104
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total cash equivalents and marketable securities	18,617	16,731
Contingent consideration liability	285	260
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total cash equivalents and marketable securities	14,450	13,574
Contingent consideration liability	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total cash equivalents and marketable securities	4,167	3,157
Contingent consideration liability	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Total cash equivalents and marketable securities	0	0
Contingent consideration liability	285	260
Fair Value, Measurements, Recurring | U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	5,183	5,948
Fair Value, Measurements, Recurring | U.S. government securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	5,183	5,948
Fair Value, Measurements, Recurring | U.S. government securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	0	0
Fair Value, Measurements, Recurring | U.S. government securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	0	0
Fair Value, Measurements, Recurring | U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	4,815	4,475
Fair Value, Measurements, Recurring | U.S. government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	4,815	4,475
Fair Value, Measurements, Recurring | U.S. government agency securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	0	0
Fair Value, Measurements, Recurring | U.S. government agency securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	0	0
Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	4,167	3,104
Fair Value, Measurements, Recurring | Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	0	0
Fair Value, Measurements, Recurring | Corporate debt securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	4,167	3,104
Fair Value, Measurements, Recurring | Corporate debt securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Marketable securities	0	0
Fair Value, Measurements, Recurring | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	4,452	2,409
Fair Value, Measurements, Recurring | Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	4,452	2,409
Fair Value, Measurements, Recurring | Money market funds | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	0	0
Fair Value, Measurements, Recurring | Money market funds | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents	$ 0	0
Fair Value, Measurements, Recurring | U.S. government securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		597
Fair Value, Measurements, Recurring | U.S. government securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		597
Fair Value, Measurements, Recurring | U.S. government securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		0
Fair Value, Measurements, Recurring | U.S. government securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		0
Fair Value, Measurements, Recurring | U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		145
Fair Value, Measurements, Recurring | U.S. government agency securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		145
Fair Value, Measurements, Recurring | U.S. government agency securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		0
Fair Value, Measurements, Recurring | U.S. government agency securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		0
Fair Value, Measurements, Recurring | Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		53
Fair Value, Measurements, Recurring | Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		0
Fair Value, Measurements, Recurring | Corporate debt securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		53
Fair Value, Measurements, Recurring | Corporate debt securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash equivalents		$ 0