Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 232.6	$ 286.7	$ 233.3	$ 295.9
Charge-Offs	(4.9)	(6.1)	(10.2)	(13.6)
Recoveries	2.5	3.5	5.1	6.4
Net (Charge-Offs) Recoveries	(2.4)	(2.6)	(5.1)	(7.2)
Provision for Credit Losses	(3.0)	(10.0)	(1.0)	(14.5)
Effect of Foreign Exchange Rates	(0.1)	0.1	(0.1)	0.0
Balance at end of period	227.1	274.2	227.1	274.2
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	115.2	164.3	114.8	169.7
Charge-Offs	(0.9)	(2.5)	(4.4)	(5.2)
Recoveries	1.3	2.4	2.5	4.1
Net (Charge-Offs) Recoveries	0.4	(0.1)	(1.9)	(1.1)
Provision for Credit Losses	(3.2)	(11.6)	(0.5)	(15.9)
Effect of Foreign Exchange Rates	(0.1)	0.1	(0.1)	0.0
Balance at end of period	112.3	152.7	112.3	152.7
Personal
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	117.4	122.4	118.5	126.2
Charge-Offs	(4.0)	(3.6)	(5.8)	(8.4)
Recoveries	1.2	1.1	2.6	2.3
Net (Charge-Offs) Recoveries	(2.8)	(2.5)	(3.2)	(6.1)
Provision for Credit Losses	0.2	1.6	(0.5)	1.4
Effect of Foreign Exchange Rates	0.0	0.0	0.0	0.0
Balance at end of period	$ 114.8	$ 121.5	$ 114.8	$ 121.5