Components of Net Interest Income (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Interest Income
Loans and Leases	$ 828.6	$ 938.7	$ 932.6
Securities - Taxable	250.6	223.6	186.0
- Non-Taxable	17.7	25.0	29.5
Interest-Bearing Deposits with Banks	176.4	192.8	134.6
Federal Reserve Deposits and Other	14.4	28.5	14.0
Total Interest Income	1,287.7	1,408.6	1,296.7
Interest Expense
Deposits	156.7	230.0	201.0
Federal Funds Purchased	1.2	1.9	4.8
Securities Sold under Agreements to Repurchase	0.4	0.7	1.0
Other Borrowings	4.0	5.5	5.4
Senior Notes	72.0	64.4	48.6
Long-Term Debt	60.3	94.6	114.8
Floating Rate Capital Debt	2.8	2.4	2.4
Total Interest Expense	297.4	399.5	378.0
Net Interest Income	$ 990.3	$ 1,009.1	$ 918.7

Interest expense incurred during the reporting period on senior notes.

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Interest Income, Federal Reserve Deposits and Other

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Represents the total of interest and dividend income, including any amortization and accretion (as applicable) of discounts and premiums, earned from (1) loans and leases whether held-for-sale or held-in-portfolio; (2) investment securities; (3) federal funds sold; (4) securities purchased under agreements to resell; (5) investments in banker's acceptances, commercial paper, or certificates of deposit; (6) dividend income; or (7) other investments not otherwise specified herein.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.1-5)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 1, 2 , 3, 4, 5

-Article 9

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-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

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-Paragraph 9, 51, 54

-IssueDate 2006-05-01

-Chapter 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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The aggregate interest and fee income generated by: (1) loans the Entity has positive intent and ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (a) industrial and agricultural; (b) real estate; and (c) real estate construction loans; (d) trade financing; (e) lease financing; (f) home equity lines-of-credit; (g) automobile and other vehicle loans; and (h) credit card and other revolving-type loans and (2) loans and leases held-for-sale which may include mortgage loans, direct financing, and sales-type leases.

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The cost of borrowed funds accounted for as interest that was charged against earnings during the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 9

-Article 9

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-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Section 563c.102

-Paragraph 9

-Chapter V

-Subsection II

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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 34

-Paragraph 21

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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-Name Accounting Standards Codification

-Topic 835

-SubTopic 20

-Section 50

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-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.9)

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Aggregate amount of interest expense on all deposits.

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-Topic 942

-SubTopic 225

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-Paragraph 1

-Subparagraph (SX 210.9-04.6)

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-Section 563c.102

-Paragraph 6

-Chapter V

-Subsection II

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Gross expenses on the purchase of Federal funds at a specified price with a simultaneous agreement to sell the same to the same counterparty at a fixed or determinable price at a future date.

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-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Section 563c.102

-Paragraph 7

-Chapter V

-Subsection II

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Interest expense incurred during the reporting period on junior subordinated debentures. Includes amortization of expenses incurred in the issuance of subordinated notes and debentures.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Paragraph 8

-Article 9

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

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-Subparagraph (SX 210.9-04.8)

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Interest expense incurred on all other long-term debt, which may include (1) interest on long-term notes, and (2) amortization of issuance costs not otherwise separately disclosed.

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-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Section 563c.102

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-Subsection I

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Interest expense incurred during the reporting period on other short-term borrowings.

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Gross expenses on securities sold coupled with an agreement to repurchase the same from the same counterparty at a fixed or determinable price within a fixed or variable time period.

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Interest income derived from funds deposited with both domestic and foreign financial institutions including funds in money market and other accounts.

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The net amount of operating interest income (expense).

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Interest income derived from investment securities which are subject to federal income taxes.

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Interest income derived from securities which are exempt from federal income taxes.

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