Financial Instruments - Fair Value of Derivatives Segregated between those Derivatives that are Designated as Hedging Instruments and those that are Not Designated as Hedging Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	$ 483	$ 454
Fair Value of Derivative, Liability	110	160
U.S Dollar Notional Amount	28,359	29,742
Derivatives Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	330	338
Fair Value of Derivative, Liability	10	89
U.S Dollar Notional Amount	14,651	14,390
Derivatives Not Designated as Hedging Instruments
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	153	116
Fair Value of Derivative, Liability	100	71
U.S Dollar Notional Amount	13,708	15,352
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Other Assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	22	0
U.S Dollar Notional Amount	3,400	0
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Accrued and other current liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	3	0
U.S Dollar Notional Amount	1,250	0
Interest rate swap contracts | Derivatives Designated as Hedging Instruments | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	0	81
U.S Dollar Notional Amount	0	4,650
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other Assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	56	75
U.S Dollar Notional Amount	2,073	2,655
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Accrued and other current liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	6	7
U.S Dollar Notional Amount	775	774
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	1	1
U.S Dollar Notional Amount	9	89
Foreign exchange contracts | Derivatives Designated as Hedging Instruments | Other current assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	252	263
U.S Dollar Notional Amount	7,144	6,222
Foreign exchange contracts | Derivatives Not Designated as Hedging Instruments | Accrued and other current liabilities
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Liability	100	71
U.S Dollar Notional Amount	6,906	9,922
Foreign exchange contracts | Derivatives Not Designated as Hedging Instruments | Other current assets
Derivatives, Fair Value [Line Items]
Fair Value of Derivative, Asset	153	116
U.S Dollar Notional Amount	$ 6,802	$ 5,430