Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 189.0	$ 232.6	$ 192.0	$ 233.3
Charge-Offs	(5.0)	(4.9)	(9.7)	(10.2)
Recoveries	1.8	2.5	4.5	5.1
Net (Charge-Offs) Recoveries	(3.2)	(2.4)	(5.2)	(5.1)
Provision for Credit Losses	(7.0)	(3.0)	(8.0)	(1.0)
Effect of Foreign Exchange Rates	0.0	(0.1)	0.0	(0.1)
Balance at end of period	178.8	227.1	178.8	227.1
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	111.8	115.2	104.9	114.8
Charge-Offs	(3.5)	(0.9)	(4.6)	(4.4)
Recoveries	0.9	1.3	2.5	2.5
Net (Charge-Offs) Recoveries	(2.6)	0.4	(2.1)	(1.9)
Provision for Credit Losses	(11.9)	(3.2)	(5.5)	(0.5)
Effect of Foreign Exchange Rates	0.0	(0.1)	0.0	(0.1)
Balance at end of period	97.3	112.3	97.3	112.3
Personal
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	77.2	117.4	87.1	118.5
Charge-Offs	(1.5)	(4.0)	(5.1)	(5.8)
Recoveries	0.9	1.2	2.0	2.6
Net (Charge-Offs) Recoveries	(0.6)	(2.8)	(3.1)	(3.2)
Provision for Credit Losses	4.9	0.2	(2.5)	(0.5)
Effect of Foreign Exchange Rates	0.0	0.0	0.0	0.0
Balance at end of period	$ 81.5	$ 114.8	$ 81.5	$ 114.8