Loans TDR modifications (parenthetical) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Financing Receivable, Impaired [Line Items]
PrincipalForgivenessRestructuringImpact	$ 9,000,000	$ 17,000,000
Number of Loans Discharged but Not Reaffirmed in Chapter 7 Bankruptcy Moved to Nonaccrual	4,231
Loans Discharged but Not Reaffirmed in Chapter 7 Bankruptcy Moved to Nonaccrual	232,000,000
Amortized cost of newly designated troulbed debt restructuring [Member] [Member]
Financing Receivable, Impaired [Line Items]
Loans Discharged but Not Reaffirmed in Chapter 7 Bankruptcy Moved to Nonaccrual	$ 201,000,000