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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Period remaining on line of credit facility before it terminates, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease) of the credit facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Data Type:	na
Balance Type:
Period Type:

- Details

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- Details

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Balance Type:
Period Type:

- Details

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Balance Type:
Period Type:

- Details

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Debt - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
Debt - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2017	Jan. 31, 2018	Dec. 31, 2016
Maximum [Member]
Debt Instrument [Line Items]
Expiration period	18 months
Revolving Credit Facilities [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Expiration period	5 years
Senior Notes [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	3.27%
Face amount of debt	$ 37,300
Senior Notes [Member] \| Senior Notes Issued By Subsidiaries in Canada and Mexico [Member]
Debt Instrument [Line Items]
Face amount of debt	$ 821
Senior Notes [Member] \| 6.75% Senior Notes Due June 2018 [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	6.75%
Face amount of debt	$ 500
Line of Credit [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	7.28%
Debt instrument term	4 years
Line of Credit [Member] \| Revolving Credit Facilities [Member]
Debt Instrument [Line Items]
Increase in unsecured committed credit facilities	$ 2,900
Unsecured Debt [Member]
Debt Instrument [Line Items]
Issuance costs	$ 122		$ 110
Secured Debt [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	2.37%
Issuance costs	$ 90		$ 75
Secured Debt [Member] \| Securitization Notes Payable [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	2.10%
Face amount of debt	$ 22,400
International [Member] \| Line of Credit [Member]
Debt Instrument [Line Items]
Increase in unsecured committed credit facilities	24
Parent Company [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Face amount of debt	$ 12,700
Parent Company [Member] \| Senior Notes [Member] \| Fixed Rate Senior Notes [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)	2.85%
Subsequent Event [Member] \| Parent Company [Member] \| Senior Notes [Member]
Debt Instrument [Line Items]
Weighted average interest rate (percent)		3.26%
Face amount of debt		$ 1,650