Investment Securities - Amount of Gross Gains and Losses Realized through Sales of Available-for-sale Investment Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments [Abstract]
Realized gains	$ 1	$ 5
Realized losses	(1)
Net realized gains (losses)		5
Income tax (benefit) on net realized gains (losses)		$ 2

Available For Sale Securities Gross Realized Gain Loss Excluding Other Than Temporary Impairments Income Tax Expense Benefit.

No definition available.

+ Details

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- Definition

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26805-111562

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- Details

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- Definition

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

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- Definition

This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities and excluding other than temporary impairments (OTTI), if any, recognized elsewhere.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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