Foreign Exchange Risk Management Classification of Outstanding Forward Contracts (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Accounts receivable
Foreign Exchange Risk Management
Forward contracts to purchase and sell foreign currency - Balance sheet location - Accounts receivable/Prepaid expenses and other current assets	$ 0	$ 6
Prepaid Expenses and Other Current Assets
Foreign Exchange Risk Management
Forward contracts to purchase and sell foreign currency - Balance sheet location - Accounts receivable/Prepaid expenses and other current assets	37	0
Other current liabilities
Foreign Exchange Risk Management
Forward contracts to purchase and sell foreign currency - Balance sheet location - Other current liabilities	(5)	(30)
Commitments to purchase foreign currency \| Foreign Exchange Forward
Foreign Exchange Risk Management
Commitments/Options to purchase/sell foreign currency, Notional	51	27
Commitments/Options to purchase/sell foreign currency, Estimated Fair Value	(1)	0
Commitments/Options to sell foreign currency \| Foreign Exchange Forward
Foreign Exchange Risk Management
Commitments/Options to purchase/sell foreign currency, Notional	969	968
Commitments/Options to purchase/sell foreign currency, Estimated Fair Value	24	(26)
Commitments/Options to sell foreign currency \| Foreign Exchange Option
Foreign Exchange Risk Management
Commitments/Options to purchase/sell foreign currency, Notional	28	27
Commitments/Options to purchase/sell foreign currency, Estimated Fair Value	$ 9	$ 2

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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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

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Fair value as of the balance sheet date of all foreign currency derivative liabilities not designated as hedging instruments.

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