Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 192.0	$ 233.3
Charge-Offs	(4.7)	(5.3)
Recoveries	2.7	2.6
Net (Charge-Offs) Recoveries	(2.0)	(2.7)
Provision for Credit Losses	(1.0)	2.0
Balance at end of period	189.0	232.6
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	104.9	114.8
Charge-Offs	(1.1)	(3.5)
Recoveries	1.6	1.2
Net (Charge-Offs) Recoveries	0.5	(2.3)
Provision for Credit Losses	6.4	2.7
Balance at end of period	111.8	115.2
Personal
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	87.1	118.5
Charge-Offs	(3.6)	(1.8)
Recoveries	1.1	1.4
Net (Charge-Offs) Recoveries	(2.5)	(0.4)
Provision for Credit Losses	(7.4)	(0.7)
Balance at end of period	$ 77.2	$ 117.4