Investment Securities (Cash Flow Model Inputs Used to Calculate Credit Losses on Certain Non-agency Mortgage-Backed Securities with Other-Than-Temporary Impairment) (Details)	Sep. 30, 2011
Significant Inputs Range, Minimum [Member]
Prepayment CPR	6.00%
Projected cumulative default	11.00%
Credit support	0.00%
Loss severity	33.00%
Significant Inputs Range, Maximum [Member]
Prepayment CPR	25.00%
Projected cumulative default	56.00%
Credit support	18.00%
Loss severity	57.00%