Components of Net Interest Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Interest Income
Loans and Leases	$ 185.5	$ 205.8	$ 373.1	$ 423.4
Securities - Taxable	48.5	65.4	106.7	127.8
- Non-Taxable	3.0	4.5	6.3	9.8
Interest-Bearing Deposits with Banks	34.5	43.5	69.5	94.0
Federal Reserve Deposits and Other	3.8	2.3	6.4	7.5
Total Interest Income	275.3	321.5	562.0	662.5
Interest Expense
Deposits	25.0	32.7	54.1	79.1
Federal Funds Purchased	0.3	0.6	0.7	0.9
Securities Sold Under Agreements to Repurchase	0.1	0.1	0.2	0.2
Other Borrowings	1.0	1.2	1.6	2.1
Senior Notes	19.3	16.8	38.5	33.8
Long-Term Debt	8.9	15.3	19.5	34.4
Floating Rate Capital Debt	0.6	0.7	1.2	1.5
Total Interest Expense	55.2	67.4	115.8	152.0
Net Interest Income	$ 220.1	$ 254.1	$ 446.2	$ 510.5