Fair Value Measurements, Derivative Assets & Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Cumulative Amount of Fair Value Hedging Adjustment - Increase (Decrease) Included in Carrying Amount of Liability	$ (120)	$ (70)
Long-term Obligations [Member]
Derivatives, Fair Value [Line Items]
Hedged Liability, Fair Value Hedge	3,261	3,309
Cumulative Amount of Fair Value Hedging Adjustment - Increase (Decrease) Included in Carrying Amount of Liability	(120)	(70)
Hedged Liability, Discontinued Fair Value Hedge, Cumulative Increase (Decrease)	40	43
Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional Amount Of Derivatives	3,100	3,100
Interest Rate Swaps [Member] \| Derivatives Designated as Hedging Instrument [Member] \| Other Long-term Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value	162	124
Currency Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional Amount Of Derivatives	2,980	2,920
Currency Exchange Contracts [Member] \| Derivatives Not Designated as Hedging Instrument [Member] \| Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value	7	10
Currency Exchange Contracts [Member] \| Derivatives Not Designated as Hedging Instrument [Member] \| Other Accrued Expenses [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value	3	15
Fair Value, Measurements, Recurring [Member]
Derivatives, Fair Value [Line Items]
Total Derivative Assets	7	10
Total Derivative Liabilities	$ 165	$ 139

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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