Securitization Activities (Summary Of Retained Interests In SPEs) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Residential Mortgage-Backed Securities [Member]
Securitization Activities [Line Items]
U.S. government agency residential mortgage-backed securities	$ 11,480.4	$ 19,196.9
Retained Interests	162.0	226.9
Commercial Mortgage-Backed Securities [Member]
Securitization Activities [Line Items]
U.S. government agency commercial mortgage-backed securities	2,831.3	5,848.5
Retained Interests	213.2	204.7
Collateralized Loan Obligations Securitizations [Member]
Securitization Activities [Line Items]
Collateralized loan obligations	3,731.7	4,511.8
Retained Interests	$ 52.3	$ 108.4