Derivative Financial Instruments and Hedging Activities - Derivatives Income (Losses) Recognized in Income (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Derivatives, Fair Value [Line Items]
Total		$ 4
Interest expense	$ 732	596
Other operating expenses	144	131
Cash Flow Hedging [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	22	(1)
Gains (Losses) Reclassified From Accumulated Other Comprehensive Loss Into Income	(21)	(3)
Cash Flow Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	4	2
Gains (Losses) Reclassified From Accumulated Other Comprehensive Loss Into Income	(3)	1
Cash Flow Hedging [Member] \| Foreign Currency Contracts [Member]
Derivatives, Fair Value [Line Items]
Gains (Losses) Recognized In Accumulated Other Comprehensive Loss	18	(3)
Gains (Losses) Reclassified From Accumulated Other Comprehensive Loss Into Income	(18)	(4)
Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts		11
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts		(1)
Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts		6
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts		(5)
Foreign currency derivatives		$ (7)
Other Operating Income (Expense) [Member]
Derivatives, Fair Value [Line Items]
Total	46
Other Operating Income (Expense) [Member] \| Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Hedged items	0
Interest rate contracts and Foreign currency contracts	0
Other Operating Income (Expense) [Member] \| Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	0
Other Operating Income (Expense) [Member] \| Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	24
Other Operating Income (Expense) [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts	0
Foreign currency derivatives	22
Interest Expense [Member]
Derivatives, Fair Value [Line Items]
Total	(8)
Interest Expense [Member] \| Designated as Hedging Instrument [Member] \| Fair Value Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Hedged items	208
Interest rate contracts and Foreign currency contracts	(210)
Interest Expense [Member] \| Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Interest Rate Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	4
Interest Expense [Member] \| Designated as Hedging Instrument [Member] \| Cash Flow Hedging [Member] \| Foreign Currency Contracts [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts and Foreign currency contracts	(9)
Interest Expense [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Interest rate contracts	6
Foreign currency derivatives	$ (7)

Hedged Liability, Fair Value Hedge

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- Definition

Amount of the increase (decrease) in fair value of the hedged item in a fair value hedge recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

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- Definition

The effective portion of net gain (loss) reclassified from accumulated other comprehensive income into income on derivative instruments designated and qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624171-113959

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The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

+ References

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Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

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+ References

No definition available.

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- Definition

Amount of gain (loss) recognized in earnings in the period from the increase (decrease) in fair value of foreign currency derivatives not designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
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- Definition

Amount of gain (loss) included in earnings for the period from the increase (decrease) in fair value of interest rate derivatives not designated as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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- Definition

Amount of the cost of borrowed funds accounted for as interest expense.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
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- Definition

The total amount of other operating cost and expense items that are associated with the entity's normal revenue producing operation.

+ References

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-Name Accounting Standards Codification
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