Investment Securities - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Weighted-average maturity of available-for-sale investment securities	5 years 6 months	5 years 1 month 6 days
Weighted-average yields of available-for-sale investment securities	2.29%	2.25%
Weighted-average maturity of held-to-maturity investment securities	5 years 2 months 12 days	4 years 8 months 12 days
Weighted-average yields of held-to-maturity investment securities	2.24%	2.14%
Fair value of securities pledged	$ 8,000	$ 12,800
Fair value of securities pledged as collateral where counterparty has right to repledge or resell	$ 571	$ 689

Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions where counterparty has the right to re-pledge such.

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- Definition

The fair value as of the balance sheet date of financial instruments and other positions owned by the entity and pledged to counterparties as collateral, including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

+ Details

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- References

No definition available.

+ Details

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- Definition

Available-for-sale securities weighted-average maturities.

+ References

No definition available.

+ Details

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- Definition

Available-for-sale securities weighted-average yield as of balance sheet date.

+ References

No definition available.

+ Details

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- Definition

Held-to-maturity securities weighted-average maturities.

+ References

No definition available.

+ Details

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- Definition

Held-to-maturity securities weighted-average yield as of balance sheet date.

+ References

No definition available.

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