Components of Net Interest Income (Detail) (USD $) In Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Interest Income
Loans and Leases	$ 229.8	$ 231.9	$ 719.5	$ 687.0
Securities - Taxable	54.8	47.7	160.4	142.5
- Non-Taxable	6.1	7.3	19.1	22.1
Interest-Bearing Deposits with Banks	49.2	40.2	131.6	100.8
Federal Reserve Deposits and Other	7.2	3.1	23.2	10.0
Total Interest Income	347.1	330.2	1,053.8	962.4
Interest Expense
Deposits	50.1	53.7	187.0	135.1
Federal Funds Purchased	0.1	1.0	1.8	3.9
Securities Sold Under Agreements to Repurchase	0.1	0.2	0.6	0.7
Other Borrowings	1.4	1.4	4.3	4.0
Senior Notes	16.4	11.5	47.6	34.4
Long-Term Debt	21.6	28.1	73.4	85.8
Floating Rate Capital Debt	0.6	0.8	1.8	1.8
Total Interest Expense	90.3	96.7	316.5	265.7
Net Interest Income	$ 256.8	$ 233.5	$ 737.3	$ 696.7