Investment Securities (Schedule Of Investment Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale securities	$ 6,168.3	$ 3,708.2
Securities carried at fair value with changes recorded in net income	0.4	283.5
Total investment securities	6,469.9	4,491.1
Debt securities
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale securities	6,123.6	3,674.1
Held-to-maturity securities	0.0	243.0
Securities carried at fair value with changes recorded in net income	0.4	283.5
Equity securities
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Available-for-sale securities	44.7	34.1
Equity fund holdings issued by customers during loan work out situations	42.3	16.7
Equity securities | FRB and FHLB Securities
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Held-to-maturity securities	$ 258.9	239.7
Equity securities | Minimum
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Percentage of non-marketable equity method ownership interets	3.00%
Non-marketable investments
Schedule Of Available For Sale And Held To Maturity Securities [Line Items]
Total investment securities	$ 301.2	$ 256.4