Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Interest Income
Loans and Leases	$ 167.1	$ 291.0	$ 606.4	$ 889.8
Securities — Taxable	182.6	265.9	632.1	812.4
Securities - Non-Taxable	0.3	0.9	1.1	3.1
Interest-Bearing Due from and Deposits with Banks	2.7	18.6	20.0	55.7
Federal Reserve and Other Central Bank Deposits and Other	2.7	44.4	31.3	162.8
Total Interest Income	355.4	620.8	1,290.9	1,923.8
Interest Expense
Deposits	(3.5)	122.0	56.7	403.5
Federal Funds Purchased	0.1	2.4	2.1	22.8
Securities Sold Under Agreements to Repurchase	0.0	1.6	1.0	5.4
Other Borrowings	5.0	46.0	40.6	145.2
Senior Notes	19.1	19.6	57.0	54.0
Long-Term Debt	5.7	9.4	21.1	29.4
Floating Rate Capital Debt	0.4	2.1	3.6	6.4
Total Interest Expense	26.8	203.1	182.1	666.7
Net Interest Income	$ 328.6	$ 417.7	$ 1,108.8	$ 1,257.1

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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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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Amount of the cost of borrowed funds accounted for as interest expense.

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Aggregate amount of interest expense on all deposits.

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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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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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Amount of interest expense incurred on long-term debt classified as other, including, but not limited to, interest on long-term notes and amortization of issuance costs.

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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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Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities exempt from state, federal and other income tax.

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Amount of operating interest income, including amortization and accretion of premiums and discounts, on securities subject to state, federal and other income tax.

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