Securitization Activities (Summary Of Retained Interests In SPEs) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Residential mortgage-backed securities
Securitization Activities [Line Items]
U.S. government agency residential mortgage-backed securities	$ 9,083.2	$ 6,383.5
Retained Interests	570.9	28.2
Commercial mortgage-backed securities
Securitization Activities [Line Items]
U.S. government agency commercial mortgage-backed securities	1,724.0	2,075.7
Retained Interests	85.6	81.4
CLOs
Securitization Activities [Line Items]
CLOs	4,361.1	3,957.8
Retained Interests	17.8	20.3
Consumer and other loans
Securitization Activities [Line Items]
Retained Interests	46.5	47.8
Consumer and Other Loans Securitization Assets	$ 281.1	$ 247.6