Investment Securities (Schedule Of Debt Securities AFS - Estimated Unrealized Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
AFS
Less than 12 months, Fair Value	$ 4,067.8	$ 2,525.8
Less than 12 months, Gross Unrealized Loss	(31.8)	(38.4)
12 months or greater, Fair Value	1,209.9	29.6
12 months or greater, Gross Unrealized Loss	(33.0)	(0.9)
HTM
Less than 12 months, Fair Value		72.0
Less than 12 months, Gross Unrealized Losses		(1.8)
12 months or greater, Fair Value		49.1
12 months or greater, Gross Unrealized Losses		(2.0)
Total
Less than 12 months, Fair Value		2,597.8
Less than 12 months, Gross Unrealized Losses		(40.2)
12 months or greater, Fair Value		78.7
12 months or greater, Gross Unrealized Losses		(2.9)
Mortgage-backed Securities, U.S. government agency securities
HTM
Less than 12 months, Fair Value		68.2
Less than 12 months, Gross Unrealized Losses		(1.7)
12 months or greater, Fair Value		26.7
12 months or greater, Gross Unrealized Losses		(1.6)
State and municipal
HTM
Less than 12 months, Fair Value		3.8
Less than 12 months, Gross Unrealized Losses		(0.1)
12 months or greater, Fair Value		22.4
12 months or greater, Gross Unrealized Losses		(0.4)
Mortgage-backed Securities, U.S. government agency securities
AFS
Less than 12 months, Fair Value	3,492.2	1,589.6
Less than 12 months, Gross Unrealized Loss	(30.9)	(31.8)
12 months or greater, Fair Value	1,151.4	13.8
12 months or greater, Gross Unrealized Loss	(31.2)	(0.5)
Mortgage-backed Securities, Non-agency securities
AFS
Less than 12 months, Fair Value	2.1	56.5
Less than 12 months, Gross Unrealized Loss	0.0	(1.4)
12 months or greater, Fair Value	0.4	15.8
12 months or greater, Gross Unrealized Loss	(0.5)	(0.4)
U.S. government agency obligations
AFS
Less than 12 months, Fair Value	24.8	546.1
Less than 12 months, Gross Unrealized Loss	(0.2)	(3.9)
12 months or greater, Fair Value	0.0	0.0
12 months or greater, Gross Unrealized Loss	0.0	0.0
U.S. Treasury securities
AFS
Less than 12 months, Fair Value	199.1	299.5
Less than 12 months, Gross Unrealized Loss	(0.2)	(0.4)
12 months or greater, Fair Value	0.0	0.0
12 months or greater, Gross Unrealized Loss	0.0	0.0
State and municipal
AFS
Less than 12 months, Fair Value	0.0
Less than 12 months, Gross Unrealized Loss	0.0
12 months or greater, Fair Value	13.6
12 months or greater, Gross Unrealized Loss	(0.4)
Supranational securities
AFS
Less than 12 months, Fair Value	349.5
Less than 12 months, Gross Unrealized Loss	(0.3)
12 months or greater, Fair Value	0.0
12 months or greater, Gross Unrealized Loss	0.0
Debt securities
AFS
Less than 12 months, Fair Value	4,067.7	2,491.7
Less than 12 months, Gross Unrealized Loss	(31.6)	(37.5)
12 months or greater, Fair Value	1,165.4	29.6
12 months or greater, Gross Unrealized Loss	(32.1)	(0.9)
Equity securities
AFS
Less than 12 months, Fair Value	0.1	34.1
Less than 12 months, Gross Unrealized Loss	(0.2)	(0.9)
12 months or greater, Fair Value	44.5	0.0
12 months or greater, Gross Unrealized Loss	$ (0.9)	$ 0.0