Investment Securities (Weighted-Average Expected Maturity of Mortgage and Other Asset-Backed Debt Securities) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	4 years 7 months	4 years 11 months
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	4 years 4 months
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	5 years 10 months
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	3 years 2 months
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	3 years 1 month
Asset backed [Member]
Mortgage And Other Asset Backed Securities [Line Items]
Weighted average expected maturity	3 years 7 months