Investment Securities (Cash Flow Model Inputs Used To Calculate Credit Losses) (Details)	Mar. 31, 2019
Minimum [Member]
Investment [Line Items]
Prepayment CPR	0.00%
Projected cumulative default	8.00%
Credit support	0.00%
Loss severity	11.00%
Maximum [Member]
Investment [Line Items]
Prepayment CPR	37.00%
Projected cumulative default	50.00%
Credit support	20.00%
Loss severity	63.00%