Fair Value Measurement of Assets and Liabilities - Financial Assets and Liabilities Measured at Fair Value, Recurring (Details) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Assets:
Derivatives	$ 92,000,000
Liabilities:
Derivatives	0
Recurring
Assets:
Cash and cash equivalents	897,000,000	$ 2,202,000,000
Total financial assets	4,533,000,000	8,812,000,000
Recurring | Short-term investments:
Assets:
Investments	2,189,000,000	2,713,000,000
Recurring | Derivatives
Assets:
Derivatives	311,000,000	262,000,000
Recurring | Long-term Investments
Assets:
Investments	1,136,000,000	3,635,000,000
Recurring | Derivatives
Liabilities:
Derivatives	15,000,000	48,000,000
Recurring | Restricted cash | Short-term investments:
Assets:
Investments	12,000,000	17,000,000
Recurring | Corporate debt securities | Short-term investments:
Assets:
Investments	2,177,000,000	2,606,000,000
Recurring | Corporate debt securities | Long-term Investments
Assets:
Investments	1,136,000,000	3,635,000,000
Recurring | Government and agency securities | Short-term investments:
Assets:
Investments		90,000,000
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets:
Cash and cash equivalents	897,000,000	2,052,000,000
Total financial assets	909,000,000	2,069,000,000
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Short-term investments:
Assets:
Investments	12,000,000	17,000,000
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives
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) | Derivatives
Liabilities:
Derivatives	0	0
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Restricted cash | Short-term investments:
Assets:
Investments	12,000,000	17,000,000
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	150,000,000
Total financial assets	3,420,000,000	6,595,000,000
Recurring | Significant Other Observable Inputs (Level 2) | Short-term investments:
Assets:
Investments	2,177,000,000	2,696,000,000
Recurring | Significant Other Observable Inputs (Level 2) | Derivatives
Assets:
Derivatives	107,000,000	114,000,000
Recurring | Significant Other Observable Inputs (Level 2) | Long-term Investments
Assets:
Investments	1,136,000,000	3,635,000,000
Recurring | Significant Other Observable Inputs (Level 2) | Derivatives
Liabilities:
Derivatives	15,000,000	48,000,000
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	2,177,000,000	2,606,000,000
Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities | Long-term Investments
Assets:
Investments	1,136,000,000	3,635,000,000
Recurring | Significant Other Observable Inputs (Level 2) | Government and agency securities | Short-term investments:
Assets:
Investments		90,000,000
Recurring | Significant Unobservable Inputs (Level 3)
Assets:
Cash and cash equivalents	0	0
Total financial assets	204,000,000	148,000,000
Recurring | Significant Unobservable Inputs (Level 3) | Short-term investments:
Assets:
Investments	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Derivatives
Assets:
Derivatives	204,000,000	148,000,000
Recurring | Significant Unobservable Inputs (Level 3) | Long-term Investments
Assets:
Investments	0	0
Recurring | Significant Unobservable Inputs (Level 3) | Derivatives
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