Financial Instruments - Derivatives, Other Information (Details) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2018 USD ($) instrument	Dec. 31, 2017 USD ($) instrument
Derivative instruments in cash flow hedges \| Forward-starting interest rate swaps
Derivative Financial Instruments
Number of derivative instruments outstanding \| instrument	0	0
Derivative instruments in cash flow hedges \| Foreign exchange forward contracts
Derivative Financial Instruments
Maximum length of time hedged	4 years
Notional amount	$ 8,200	$ 7,800
Average remaining maturity	8 months 12 days	8 months 12 days
Net gains (losses) before taxes in other comprehensive income/(loss), cash flow hedges	$ (46)	$ 27
Gains (losses) expected to be reclassified to net income within the next 12 months	$ (137)
Derivative instruments in cash flow hedges \| Cross-currency swaps
Derivative Financial Instruments
Maximum length of time hedged	10 years
Notional amount	$ 6,500	6,500
Net gains (losses) before taxes in other comprehensive income/(loss), cash flow hedges	122	42
Gains (losses) expected to be reclassified to net income within the next 12 months	194
Instruments in net investment hedges
Derivative Financial Instruments
Notional amount	$ 6,700	$ 7,000
Average remaining maturity	2 months 12 days	2 months 12 days
Designated as hedging instruments \| Interest rate swaps
Derivative Financial Instruments
Notional amount	$ 9,900	$ 9,100
Average remaining maturity	4 years 9 months 18 days	4 years 9 months 18 days
Not designated as hedging instruments - economic hedges \| Foreign exchange contracts
Derivative Financial Instruments
Notional amount	$ 8,900	$ 11,500
Not designated as hedging instruments - economic hedges \| Foreign exchange contracts \| Maximum
Derivative Financial Instruments
Term of contract	1 year
Not designated as hedging instruments - economic hedges \| Equity contracts hedging employee compensation obligations
Derivative Financial Instruments
Notional amount	$ 1,200	$ 1,300
Not designated as hedging instruments - economic hedges \| Equity contracts hedging investment securities
Derivative Financial Instruments
Number of derivative instruments outstanding \| instrument	0	0
Not designated as hedging instruments - economic hedges \| Warrants qualifying as derivatives
Derivative Financial Instruments
Number of derivative instruments outstanding \| instrument	0	0
Not designated as hedging instruments - economic hedges \| Credit default swaps
Derivative Financial Instruments
Number of derivative instruments outstanding \| instrument	0	0

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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Amount before tax of increase (decrease) in accumulated equity from transactions and other events and circumstances from non-owner sources, attributable to parent. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners).

+ 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

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- Definition

Average remaining period until maturity of the derivative contract, 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

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

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- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

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Period the derivative contract is outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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- Definition

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994

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