Commitments and Contingencies - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Commitment and Contingencies [Line Items]
Estimate of possible loss	$ 70
Loss contingency accrual	23
Indirect tax contingency	19
Senior Notes [Member]
Commitment and Contingencies [Line Items]
Face amount of debt	37,300
Senior Notes [Member] \| Parent Company [Member]
Commitment and Contingencies [Line Items]
Face amount of debt	12,700
Senior Notes [Member] \| Senior Notes Issued By Subsidiaries in Canada and Mexico [Member]
Commitment and Contingencies [Line Items]
Face amount of debt	821
Senior Notes [Member] \| Euro Medium Term Notes [Member] \| Parent Company [Member]
Commitment and Contingencies [Line Items]
Face amount of debt	$ 2,000
Accounts Receivable [Member] \| Geographic Concentration Risk [Member]
Commitment and Contingencies [Line Items]
Concentration risk (percent)	12.80%
Administrative Offices And Other [Member] \| Maximum [Member]
Commitment and Contingencies [Line Items]
Term of contract	10 years

[Line Items] for Commitment and Contingencies [Table]

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- Definition

Indirect Tax Contingency

+ References

No definition available.

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

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- Definition

Amount of loss contingency liability.

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Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

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