Components of Net Interest Income (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Interest Income
Loans and Leases	$ 183.9		$ 182.9
Securities - Taxable	76.6		69.5
Securities - Non-Taxable	1.3		2.2
Interest-Bearing Due from and Deposits with Banks	26.6	[1]	32.1	[1]
Federal Reserve Deposits and Other	10.4		8.7
Total Interest Income	298.8		295.4
Interest Expense
Deposits	16.7		20.1
Federal Funds Purchased	0.2		0.3
Securities Sold Under Agreements to Repurchase	0.1		0.1
Other Borrowings	1.2		0.7
Senior Notes	11.6		17.5
Long-Term Debt	7.8		10.4
Floating Rate Capital Debt	0.6		0.6
Total Interest Expense	38.2		49.7
Net Interest Income	$ 260.6		$ 245.7

[1] Interest income for the three months ended March 31, 2015, was earned on cash and due from banks of $2.2 billion and interest-bearing deposits with banks of $15.4 billion as of March 31, 2015.