Financial Instruments (Fair Value of Foreign Exchange Contracts) (Details) - Foreign Exchange Contract [Member] - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 140	$ 813
Liability Derivatives	1,128	163
Designated as Hedging Instrument [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	84	207
Designated as Hedging Instrument [Member] | Other accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	197	66
Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	34	436
Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	880	36
Not Designated as Hedging Instrument [Member] | Other current assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	22	161
Not Designated as Hedging Instrument [Member] | Other accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	37	61
Not Designated as Hedging Instrument [Member] | Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives	0	9
Not Designated as Hedging Instrument [Member] | Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives	$ 14	$ 0