Guarantees - Additional Information (Details) - USD ($) shares in Millions, $ in Millions	1 Months Ended
May 31, 2009	Sep. 30, 2018	Dec. 31, 2017
Derivative Liability, Fair Value, Gross Asset		$ 2,185	$ 2,731
Standby Letters of Credit [Member]
Guarantor Obligations, Maximum Exposure, Undiscounted		3,100	2,600
Visa Interest [Member]
Derivative Liability, Fair Value, Gross Asset		7	15
Not Designated as Hedging Instrument [Member] \| Derivative Financial Instruments, Liabilities [Member] \| Visa Interest [Member]
Number Of Shares Sold To Selected Financial Institutions	3.2
Guarantee of Indebtedness of Others [Member]
Loss Contingency Related Loans Unpaid Principal Balance		3,400	3,400
Guarantor Obligations, Maximum Exposure, Undiscounted		978
Loss Contingency Accrual, at Carrying Value		$ 12	$ 11

Unpaid principal balance outstanding of loans sold related to commercial mortgage recourse obligations.

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- Definition

Number of shares sold to selected financial institutions.

+ References

No definition available.

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- Definition

Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226003-175313

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (a),(c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624163-113959

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- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=115931803&loc=d3e12069-110248

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- Definition

Amount of loss contingency liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

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