Components of Net Interest Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Interest Income
Loans and Leases	$ 184.8	$ 185.4	$ 553.5	$ 558.5
Securities - Taxable	65.1	60.9	198.0	167.6
- Non-Taxable	1.6	2.7	5.7	9.0
Interest-Bearing Deposits with Banks	30.9	36.3	96.6	105.8
Federal Reserve Deposits and Other	11.4	5.8	29.2	12.2
Total Interest Income	293.8	291.1	883.0	853.1
Interest Expense
Deposits	21.6	25.8	64.1	79.9
Federal Funds Purchased	0.5	0.4	1.1	1.0
Securities Sold Under Agreements to Repurchase	0.1	0.1	0.3	0.3
Other Borrowings	0.9	0.8	2.4	2.5
Senior Notes	11.6	18.4	42.8	56.9
Long-Term Debt	9.2	8.0	29.0	27.5
Floating Rate Capital Debt	0.6	0.6	1.7	1.8
Total Interest Expense	44.5	54.1	141.4	169.9
Net Interest Income	$ 249.3	$ 237.0	$ 741.6	$ 683.2