Fair Value Measurements - Recurring Basis (Details) - Recurring - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	$ 2,990	$ 1,667
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	2,921	1,613
Foreign government treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	38	34
Auction rate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	9	9
Not Designated as Hedges | Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value		11
Designated as Hedges | Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	22
Liabilities measured at fair value on a recurring basis, gain loss included in earnings
Total liabilities at fair value		(4)
Fair value measurements using quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	2,959	1,647
Fair value measurements using quoted prices in active markets for identical assets (Level 1) | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	2,921	1,613
Fair value measurements using quoted prices in active markets for identical assets (Level 1) | Foreign government treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	38	34
Fair value measurements using quoted prices in active markets for identical assets (Level 1) | Auction rate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Fair value measurements using quoted prices in active markets for identical assets (Level 1) | Not Designated as Hedges | Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value		0
Fair value measurements using quoted prices in active markets for identical assets (Level 1) | Designated as Hedges | Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0
Liabilities measured at fair value on a recurring basis, gain loss included in earnings
Total liabilities at fair value		0
Fair value measurements using significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	22	11
Fair value measurements using significant other observable inputs (Level 2) | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Fair value measurements using significant other observable inputs (Level 2) | Foreign government treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Fair value measurements using significant other observable inputs (Level 2) | Auction rate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Fair value measurements using significant other observable inputs (Level 2) | Not Designated as Hedges | Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value		11
Fair value measurements using significant other observable inputs (Level 2) | Designated as Hedges | Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	22
Liabilities measured at fair value on a recurring basis, gain loss included in earnings
Total liabilities at fair value		(4)
Fair value measurements using significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	9	9
Fair value measurements using significant unobservable inputs (Level 3) | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Fair value measurements using significant unobservable inputs (Level 3) | Foreign government treasury bills
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	0	0
Fair value measurements using significant unobservable inputs (Level 3) | Auction rate securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	9	9
Fair value measurements using significant unobservable inputs (Level 3) | Not Designated as Hedges | Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value		0
Fair value measurements using significant unobservable inputs (Level 3) | Designated as Hedges | Foreign currency forward contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets at fair value	$ 0
Liabilities measured at fair value on a recurring basis, gain loss included in earnings
Total liabilities at fair value		$ 0