Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 274.2	$ 303.5	$ 295.9	$ 307.9
Charge-Offs	(11.9)	(8.6)	(25.5)	(27.9)
Recoveries	2.5	3.4	8.9	15.3
Net (Charge-Offs) Recoveries	(9.4)	(5.2)	(16.6)	(12.6)
Provision for Credit Losses	(10.0)	0.0	(24.5)	3.0
Effect of Foreign Exchange Rates	(0.1)	0.0	(0.1)	0.0
Balance at end of period	254.7	298.3	254.7	298.3
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	152.7	168.7	169.7	168.0
Charge-Offs	(7.7)	(2.5)	(12.9)	(8.8)
Recoveries	0.5	1.9	4.6	10.7
Net (Charge-Offs) Recoveries	(7.2)	(0.6)	(8.3)	1.9
Provision for Credit Losses	(6.2)	1.0	(22.1)	(0.8)
Effect of Foreign Exchange Rates	(0.1)	0.0	(0.1)	0.0
Balance at end of period	139.2	169.1	139.2	169.1
Personal
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	121.5	134.8	126.2	139.9
Charge-Offs	(4.2)	(6.1)	(12.6)	(19.1)
Recoveries	2.0	1.5	4.3	4.6
Net (Charge-Offs) Recoveries	(2.2)	(4.6)	(8.3)	(14.5)
Provision for Credit Losses	(3.8)	(1.0)	(2.4)	3.8
Effect of Foreign Exchange Rates	0.0	0.0	0.0	0.0
Balance at end of period	$ 115.5	$ 129.2	$ 115.5	$ 129.2