Fair Value Measurement of Assets and Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivatives	$ 84
Derivative liabilities	1
Fair Value, Measurements, Recurring
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash and cash equivalents	2,202	$ 2,120
Derivatives		28
Total financial assets	8,812	11,337
Fair Value, Measurements, Recurring | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	2,713	3,743
Fair Value, Measurements, Recurring | Other Current Assets
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivatives	262
Fair Value, Measurements, Recurring | Long-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	3,635	5,446
Fair Value, Measurements, Recurring | Other Current Liabilities
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative liabilities	48	29
Fair Value, Measurements, Recurring | Restricted cash | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	17	20
Fair Value, Measurements, Recurring | Corporate debt securities | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	2,606	3,723
Fair Value, Measurements, Recurring | Corporate debt securities | Long-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	3,635	5,446
Fair Value, Measurements, Recurring | Government and agency securities | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	90
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash and cash equivalents	2,052	2,120
Derivatives		0
Total financial assets	2,069	2,140
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	17	20
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Current Assets
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivatives	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Current Liabilities
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Restricted cash | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	17	20
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities | Long-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government and agency securities | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash and cash equivalents	150	0
Derivatives		28
Total financial assets	6,595	9,197
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	2,696	3,723
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Current Assets
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivatives	114
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Long-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	3,635	5,446
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other Current Liabilities
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative liabilities	48	29
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Restricted cash | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	2,606	3,723
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities | Long-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	3,635	5,446
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Government and agency securities | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	90
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Cash and cash equivalents	0	0
Derivatives		0
Total financial assets	148	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other Current Assets
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivatives	148
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Long-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Other Current Liabilities
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Restricted cash | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate debt securities | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0	0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate debt securities | Long-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0	$ 0
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Government and agency securities | Short-term Investments
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Investments	0
Warrant | Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	0
Recognition of warrant	44
Change in fair value	104
Ending balance	$ 148