Derivatives and Hedging Activities - Cumulative Basis Adjustments on Fair Value Hedges (Detail) - Interest Rate [Member] $ in Millions	Sep. 30, 2018 USD ($)
Long-term Debt [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged item	$ 9,442
Hedge accounting basis adjustment	(145)
Certificates of Deposit [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged item	344
Hedge accounting basis adjustment	(1)
Bank Time Deposits [Member]
Derivatives, Fair Value [Line Items]
Carrying amount of hedged item	178
Hedge accounting basis adjustment	0
Derivatives Not Designated as Hedging Instruments [Member] \| Long-term Debt [Member]
Derivatives, Fair Value [Line Items]
Hedge accounting basis adjustment	$ (10)

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.

No definition available.

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- Definition

Amount of cumulative increase (decrease) in fair value of hedged asset in fair value hedge, attributable to hedged risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959

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- Definition

Amount of liability hedged in fair value hedging relationship.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4EE
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109999712-113959

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