Derivative Instruments - Impact on Statements of Income, Cash Flow Hedges (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivatives gains/(losses) recorded in income and other comprehensive income/(loss)
Recognition of gain (loss) related to cash flow hedges in Income			$ (118)
Maximum length of time hedged in forecasted transactions, terminated cash flow hedges			6 years
Maximum length of time hedged in forecasted transactions, open cash flow hedges			6 years
Cash Flow Hedging
Derivatives gains/(losses) recorded in income and other comprehensive income/(loss)
Amounts reclassified from AOCI to income	$ (9)	$ (10)	$ 62	$ (160)
Amounts recorded in OCI	(122)	29	(365)	111
Total change in OCI for period	(113)	39	(427)	271
Cash Flow Hedging \| Interest rate
Derivatives gains/(losses) recorded in income and other comprehensive income/(loss)
Amounts reclassified from AOCI to income	10	1	36	(16)
Amounts recorded in OCI	(30)	(1)	(141)	11
Total change in OCI for period	(40)	(2)	(177)	27
Cash Flow Hedging \| Foreign exchange
Derivatives gains/(losses) recorded in income and other comprehensive income/(loss)
Amounts reclassified from AOCI to income	(19)	(11)	26	(144)
Amounts recorded in OCI	(92)	30	(224)	100
Total change in OCI for period	$ (73)	$ 41	$ (250)	$ 244

Cash flow hedge gains and losses.

No definition available.

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- Definition

For an open cash flow hedge, maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

For a terminated cash flow hedge, maximum length of time over which the entity is hedging its exposure to the variability in future cash flows for forecasted transactions, excluding those forecasted transactions related to the payment of variable interest on existing financial instruments, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=112277219&loc=d3e80748-113994

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- Definition

Amount, before tax and after reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580

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- Definition

Amount, before tax and reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

+ References

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

Amount, before tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
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-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e689-108580

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