Components of Net Interest Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Interest Income
Loans and Leases	$ 187.6	$ 217.6
Securities - Taxable	58.2	62.4
- Non-Taxable	3.3	5.2
Interest-Bearing Deposits with Banks	35.0	50.6
Federal Reserve Deposits and Other	2.6	5.2
Total Interest Income	286.7	341.0
Interest Expense
Deposits	29.1	46.3
Federal Funds Purchased	0.3	0.4
Securities Sold Under Agreements to Repurchase	0.1	0.1
Other Borrowings	0.7	1.0
Senior Notes	19.2	16.9
Long-Term Debt	10.6	19.1
Floating Rate Capital Debt	0.6	0.8
Total Interest Expense	60.6	84.6
Net Interest Income	$ 226.1	$ 256.4