Components of Net Interest Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Interest Income
Loans and Leases	$ 206.9	$ 229.8	$ 630.4	$ 719.5
Securities - Taxable	63.2	54.8	191.0	160.4
- Non-Taxable	4.1	6.1	13.9	19.1
Interest-Bearing Deposits with Banks	44.8	49.2	138.8	131.6
Federal Reserve Deposits and Other	4.1	7.2	11.5	23.2
Total Interest Income	323.1	347.1	985.6	1,053.8
Interest Expense
Deposits	43.8	50.1	122.9	187.0
Federal Funds Purchased	0.1	0.1	1.1	1.8
Securities Sold Under Agreements to Repurchase	0.1	0.1	0.3	0.6
Other Borrowings	1.2	1.4	3.3	4.3
Senior Notes	18.6	16.4	52.4	47.6
Long-Term Debt	13.0	21.6	47.3	73.4
Floating Rate Capital Debt	0.7	0.6	2.2	1.8
Total Interest Expense	77.5	90.3	229.5	316.5
Net Interest Income	$ 245.6	$ 256.8	$ 756.1	$ 737.3