Components of Net Interest Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Interest Income
Loans and Leases	$ 217.6	$ 246.4
Securities - Taxable	62.4	49.8
- Non-Taxable	5.2	6.8
Interest-Bearing Deposits with Banks	50.6	37.6
Federal Reserve Deposits and Other	5.2	6.5
Total Interest Income	341.0	347.1
Interest Expense
Deposits	46.3	66.8
Federal Funds Purchased	0.4	1.0
Securities Sold Under Agreements to Repurchase	0.1	0.3
Other Borrowings	1.0	1.2
Senior Notes	16.9	15.7
Long-Term Debt	19.1	27.1
Floating Rate Capital Debt	0.8	0.6
Total Interest Expense	84.6	112.7
Net Interest Income	$ 256.4	$ 234.4