Investment Securities (Mortgage-backed, Asset-backed Securities) (Details)	12 Months Ended
	Dec. 31, 2012
Fixed rate CMBS
Investment securities
Average basis points of subordination (as a percent)	25
Floating rate CMBS
Investment securities
Average basis points of subordination (as a percent)	50
Maximum | Commercial
Investment securities
Percentage of underlying loans reported as non-performing	1.00%