Fair Value Measurement of Assets and Liabilities - Financial Assets and Liabilities Measured at Fair Value, Recurring (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Assets:
Derivatives	$ 43
Liabilities:
Derivatives	11
Recurring
Assets:
Cash and cash equivalents	1,508	$ 2,202
Total financial assets	6,610	8,812
Recurring | Short-term Investments
Assets:
Investments	2,969	2,713
Recurring | Other Current Assets
Assets:
Derivatives	350	262
Recurring | Long-term Investments
Assets:
Investments	1,783	3,635
Recurring | Other Current Liabilities
Liabilities:
Derivatives	43	48
Recurring | Restricted cash | Short-term Investments
Assets:
Investments	13	17
Recurring | Corporate debt securities | Short-term Investments
Assets:
Investments	2,956	2,606
Recurring | Corporate debt securities | Long-term Investments
Assets:
Investments	1,783	3,635
Recurring | Government and agency securities | Short-term Investments
Assets:
Investments		90
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	1,508	2,052
Total financial assets	1,521	2,069
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term Investments
Assets:
Investments	13	17
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Current Assets
Assets:
Derivatives	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Long-term Investments
Assets:
Investments	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other Current Liabilities
Liabilities:
Derivatives	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Restricted cash | Short-term Investments
Assets:
Investments	13	17
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities | Short-term Investments
Assets:
Investments	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate debt securities | Long-term Investments
Assets:
Investments	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Government and agency securities | Short-term Investments
Assets:
Investments		0
Recurring | Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents	0	150
Total financial assets	4,836	6,595
Recurring | Significant Other Observable Inputs (Level 2) | Short-term Investments
Assets:
Investments	2,956	2,696
Recurring | Significant Other Observable Inputs (Level 2) | Other Current Assets
Assets:
Derivatives	97	114
Recurring | Significant Other Observable Inputs (Level 2) | Long-term Investments
Assets:
Investments	1,783	3,635
Recurring | Significant Other Observable Inputs (Level 2) | Other Current Liabilities
Liabilities:
Derivatives	43	48
Recurring | Significant Other Observable Inputs (Level 2) | Restricted cash | Short-term Investments
Assets:
Investments	0	0
Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities | Short-term Investments
Assets:
Investments	2,956	2,606
Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities | Long-term Investments
Assets:
Investments	1,783	3,635
Recurring | Significant Other Observable Inputs (Level 2) | Government and agency securities | Short-term Investments
Assets:
Investments		90
Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Total financial assets	253	148
Recurring | Significant Unobservable Inputs (Level 3) | Short-term Investments
Assets:
Investments	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Other Current Assets
Assets:
Derivatives	253	148
Recurring | Significant Unobservable Inputs (Level 3) | Long-term Investments
Assets:
Investments	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Other Current Liabilities
Liabilities:
Derivatives	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Restricted cash | Short-term Investments
Assets:
Investments	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Corporate debt securities | Short-term Investments
Assets:
Investments	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Corporate debt securities | Long-term Investments
Assets:
Investments	$ 0	0
Recurring | Significant Unobservable Inputs (Level 3) | Government and agency securities | Short-term Investments
Assets:
Investments		$ 0