Investment Securities (Mortgage-backed, Asset-backed Securities) (Details)	3 Months Ended
	Mar. 31, 2013
Fixed rate CMBS
Investment securities
Average basis points of subordination (as a percent)	0.25
Floating rate CMBS
Investment securities
Average basis points of subordination (as a percent)	0.30
Maximum | Commercial Mortgage Backed Securities
Investment securities
Percentage of underlying loans reported as non-performing	1.00%