Investment Securities (Weighted-Average Expected Maturity of Mortgage and Other Asset-Backed Debt Securities) (Details)	9 Months Ended
	Sep. 30, 2012
Residential mortgage-backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	3 years 3 months
Residential mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	4 years 11 months
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	4 years 11 months
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	2 years 9 months
Asset backed [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	3 years 8 months