Investment Securities (Mortgage-backed, Asset-backed Securities) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2014 Fixed rate CMBS	Jun. 30, 2014 Maximum Commercial Mortgage Backed Securities	Jun. 30, 2014 Fair Value	Dec. 31, 2013 Fair Value	Jun. 30, 2013 Fair Value	Dec. 31, 2012 Fair Value	Jun. 30, 2014 Fair Value Fixed rate CMBS	Jun. 30, 2014 Fair Value Floating rate CMBS	Jun. 30, 2014 Fair Value Commercial Mortgage Backed Securities	Dec. 31, 2013 Fair Value Commercial Mortgage Backed Securities	Jun. 30, 2014 Fair Value Non-Agency Residential Mortgage Resecuritization
Schedule of Trading Securities and Other Trading Assets [Line Items]
Average basis points of subordination	0.20
Percentage of underlying loans reported as non-performing		1.00%
Fair value investments			$ 6,777.0	$ 6,766.5	$ 6,565.5	$ 6,950.7	$ 231.5	$ 111.7	$ 343.2	$ 282.3	$ 57.6