Financial Instruments - Fair Value of Derivative Financial Instruments and Related Notional Amounts (Details) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Derivative [Line Items]
Asset		$ 1,043	$ 822
Liability		1,174	691
Designated as Hedging Instrument [Member]
Derivative [Line Items]
Asset		925	760
Liability		1,126	637
Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Notional	[1]	19,955	18,723
Asset	[1]	590	179
Liability	[1]	464	459
Designated as Hedging Instrument [Member] | Interest rate contracts [Member]
Derivative [Line Items]
Notional		11,300	12,430
Asset		335	581
Liability		661	178
Not Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Notional		16,798	14,300
Asset		118	62
Liability		48	$ 54
Inventory sales [Member] | Designated as Hedging Instrument [Member] | Foreign exchange contracts [Member]
Derivative [Line Items]
Notional	[1]	$ 5,400

[1] As of September 30, 2018, the notional amount of outstanding foreign currency forward-exchange contracts hedging our intercompany forecasted inventory sales was $5.4 billion.