Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 227.1	$ 274.2	$ 233.3	$ 295.9
Charge-Offs	(3.0)	(11.9)	(13.2)	(25.5)
Recoveries	3.8	2.5	8.9	8.9
Net (Charge-Offs) Recoveries	0.8	(9.4)	(4.3)	(16.6)
Provision for Credit Losses	(3.0)	(10.0)	(4.0)	(24.5)
Effect of Foreign Exchange Rates	0.0	(0.1)	(0.1)	(0.1)
Balance at end of period	224.9	254.7	224.9	254.7
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	112.3	152.7	114.8	169.7
Charge-Offs	(0.3)	(7.7)	(4.7)	(12.9)
Recoveries	1.0	0.5	3.5	4.6
Net (Charge-Offs) Recoveries	0.7	(7.2)	(1.2)	(8.3)
Provision for Credit Losses	4.0	(6.2)	3.5	(22.1)
Effect of Foreign Exchange Rates	0.0	(0.1)	(0.1)	(0.1)
Balance at end of period	117.0	139.2	117.0	139.2
Personal
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	114.8	121.5	118.5	126.2
Charge-Offs	(2.7)	(4.2)	(8.5)	(12.6)
Recoveries	2.8	2.0	5.4	4.3
Net (Charge-Offs) Recoveries	0.1	(2.2)	(3.1)	(8.3)
Provision for Credit Losses	(7.0)	(3.8)	(7.5)	(2.4)
Effect of Foreign Exchange Rates	0.0	0.0	0.0	0.0
Balance at end of period	$ 107.9	$ 115.5	$ 107.9	$ 115.5