Investment Securities - Additional Information (Detail) (USD $) In Billions, unless otherwise specified	Mar. 31, 2015 Security	Dec. 31, 2014 Security
Net Investment Income [Line Items]
Pledged securities, carrying values	$ 1.3	$ 1.4
Number of debt securities, held	86	112
Unrealized losses on debt securities, percent of amortized cost	0.86%	1.31%
Obligations of State and Political Obligations [Member]
Net Investment Income [Line Items]
Number of securities, continuous loss position, over twelve months	2

Number of available for sale securities continuous unrealized loss position twelve months or longer.

No definition available.

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- Definition

The number of securities held in the investment portfolio with unrealized losses at the end of the current period.

+ References

No definition available.

+ Details

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- Definition

Unrealized losses on total debt securities, gross, as a percentage of the unamortized cost basis of the securities.

+ References

No definition available.

+ Details

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- Details

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- Definition

The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5086-111524

+ Details

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- Details

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