Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Financial Instruments and Fair Value [Line Items]
Gross realized gains on the sale of our marketable securities	$ 21,000,000	$ 62,000,000	$ 193,000,000	$ 221,000,000
Gross realized losses on the sale of our marketable securities	65,000,000	12,000,000	274,000,000	347,000,000
Other-than-temporary impairment losses recognized	0	$ 0	0	$ 87,000,000
Cash collateral received from derivative financial instruments	47,000,000		47,000,000		$ 362,000,000
Effective portion of our cash flow hedges before tax effect	440,000,000		440,000,000
Foreign currency gain (loss) to be reclassified during next 12 months	473,000,000		473,000,000
Cash Flow Hedging Relationship | Foreign exchange contracts
Financial Instruments and Fair Value [Line Items]
Notional amount of derivative	11,700,000,000		$ 11,700,000,000		10,700,000,000
Foreign exchange option contracts, maximum maturities			24 months
Derivatives in Fair Value Hedging Relationship | Foreign exchange contracts
Financial Instruments and Fair Value [Line Items]
Notional amount of derivative	2,500,000,000		$ 2,500,000,000		2,400,000,000
Fair Value of Derivatives Not Designated as Hedging Instruments | Foreign exchange contracts
Financial Instruments and Fair Value [Line Items]
Notional amount of derivative	$ 17,200,000,000		$ 17,200,000,000		$ 7,900,000,000