Investment Securities (Cash Flow Model Inputs Used To Calculate Credit Losses) (Details)	Mar. 31, 2013
Significant Inputs Range, Minimum [Member]
Investment [Line Items]
Prepayment CPR	2.00%
Projected cumulative default	15.00%
Credit support	0.00%
Loss severity	17.00%
Significant Inputs Range, Maximum [Member]
Investment [Line Items]
Prepayment CPR	25.00%
Projected cumulative default	58.00%
Credit support	16.00%
Loss severity	95.00%