Contingent Liabilities and Guarantees - Guarantees (Detail) $ in Millions	Sep. 30, 2018 USD ($)
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	$ 10,695
Liability Recorded	168
Written Put Options [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	2,346
Liability Recorded	82
Standby Letters of Credit [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	3,097
Liability Recorded	71
Recourse Agreement with FNMA [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	3,750
Liability Recorded	7
Residential Mortgage Reserve [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	1,500
Liability Recorded	6
Return Guarantee Agreement with LIHTC Investors [Member]
Guarantor Obligations [Line Items]
Maximum Potential Undiscounted Future Payments	2
Liability Recorded	$ 2

The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

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 (c)
-URI http://asc.fasb.org/extlink&oid=115931803&loc=d3e12069-110248

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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

No definition available.

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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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