Loans TDR modifications (Additional Information) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012 contracts
Financing Receivable, Impaired [Line Items]
PrincipalForgivenessRestructuringImpact	$ 14	$ 2	$ 9
NumberOfLoansDischargedButNotReaffirmedInChapter7BankruptcyMovedToNonaccrual			4,231
Bankruptcy Claims, Amount of Claims Expunged by Bankruptcy Court			$ 201

The aggregate number of claims filed that the bankruptcy court has expunged.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant