Fair Value Measurements and Financial Instruments - Schedule of assets and liabilities that are measured at fair value on a recurring basis (Details) - Recurring - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Money market funds and highly liquid debt securities
Assets:
Money market funds and highly liquid debt securities	$ 1,502	$ 1,847
Government bonds
Assets:
Other investments:	1	1
Equity investments
Assets:
Other investments:	3	4
Gross foreign exchange contracts
Assets:
Derivatives	54	33
Liabilities:
Derivatives	8	6
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money market funds and highly liquid debt securities
Assets:
Money market funds and highly liquid debt securities	1,502	1,847
Quoted Prices in Active Markets for Identical Assets (Level 1) | Government bonds
Assets:
Other investments:	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity investments
Assets:
Other investments:	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Gross foreign exchange contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Significant Other Observable Inputs (Level 2) | Money market funds and highly liquid debt securities
Assets:
Money market funds and highly liquid debt securities	0	0
Significant Other Observable Inputs (Level 2) | Government bonds
Assets:
Other investments:	1	1
Significant Other Observable Inputs (Level 2) | Equity investments
Assets:
Other investments:	3	4
Significant Other Observable Inputs (Level 2) | Gross foreign exchange contracts
Assets:
Derivatives	54	33
Liabilities:
Derivatives	8	6
Significant Unobservable Inputs (Level 3) | Money market funds and highly liquid debt securities
Assets:
Money market funds and highly liquid debt securities	0	0
Significant Unobservable Inputs (Level 3) | Government bonds
Assets:
Other investments:	0	0
Significant Unobservable Inputs (Level 3) | Equity investments
Assets:
Other investments:	0	0
Significant Unobservable Inputs (Level 3) | Gross foreign exchange contracts
Assets:
Derivatives	0	0
Liabilities:
Derivatives	$ 0	$ 0