Loans and asset quality- Troubled Debt Restructurings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015 Contract	Dec. 31, 2014 Contract	Mar. 31, 2014 Contract
Financing Receivable, Modifications [Line Items]
Number of contracts (contracts)	19	22	32
Outstanding recorded investment Pre-modification	$ 4	$ 3	$ 10
Outstanding recorded investment Post- modification	4	4	9
Domestic \| Other residential mortgages
Financing Receivable, Modifications [Line Items]
Number of contracts (contracts)	19	22	31
Outstanding recorded investment Pre-modification	4	3	5
Outstanding recorded investment Post- modification	4	4	5
Foreign
Financing Receivable, Modifications [Line Items]
Number of contracts (contracts)	0	0	1
Outstanding recorded investment Pre-modification	0	0	5
Outstanding recorded investment Post- modification	$ 0	$ 0	$ 4

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Number of financing receivables that have been modified by troubled debt restructurings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 33

-URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953676-111524

+ Details

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Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

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