Northern Trust (NTRS) 10-Q 23 Apr 24 2024 Q1 Quarterly report Financial data

Cover Page

Cover Page	3 Months Ended
	Mar. 31, 2024 shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2024
Document Transition Report	false
Entity File Number	001-36609
Entity Registrant Name	NORTHERN TRUST CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	36-2723087
Entity Address, Address Line One	50 South LaSalle Street
Entity Address, City or Town	Chicago,
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60603
City Area Code	312
Local Phone Number	630-6000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)	204,591,724
Amendment Flag	false
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q1
Entity Central Index Key	0000073124
Current Fiscal Year End Date	--12-31
Common Stock, $1.66 2/3 Par Value
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, $1.66 2/3 Par Value
Trading Symbol	NTRS
Security Exchange Name	NASDAQ
Depositary Shares, each representing 1/1,000th interest in a share of Series E Non-Cumulative Perpetual Preferred Stock
Entity Information [Line Items]
Title of 12(b) Security	Depositary Shares, each representing 1/1,000th interest in a share of Series E Non-Cumulative Perpetual Preferred Stock
Trading Symbol	NTRSO
Security Exchange Name	NASDAQ

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
ASSETS
Cash and Due from Banks	$ 5,308.7	$ 4,791.5
Federal Reserve and Other Central Bank Deposits	40,269.9	34,326.2
Interest-Bearing Deposits with Banks	1,372.1	1,939
Securities Purchased under Agreements to Resell	500.1	784.7
Debt Securities
Available for Sale	25,638.9	23,089.8
Held to Maturity	23,497.9	26,221.7
Total Debt Securities	49,136.8	49,311.5
Loans
Total Loans (Net of unearned income of $6.6 and $5.9)	47,342.6	47,617
Allowance for Credit Losses	(175.8)	(192.3)
Buildings and Equipment	488	502.2
Client Security Settlement Receivables	116.4	212.6
Goodwill	697.5	702.3
Other Assets	11,054.7	10,788.4
Total Assets	156,111	150,783.1
Deposits
Demand and Other Noninterest-Bearing	16,484.5	14,246.4
Savings, Money Market and Other Interest-Bearing	25,893.5	25,252.1
Savings Certificates and Other Time	5,636.6	4,109.7
Non U.S. Offices — Noninterest-Bearing	8,842.4	8,584.7
Non U.S. Offices — Interest-Bearing	67,084.7	63,971.1
Total Deposits	123,941.7	116,164
Federal Funds Purchased	2,600.5	3,045.4
Securities Sold Under Agreements to Repurchase	511.4	784.7
Other Borrowings	6,526.2	6,567.8
Senior Notes	2,743.5	2,773.2
Long-Term Debt	4,069	4,065
Other Liabilities	3,616.9	5,485.1
Total Liabilities	144,009.2	138,885.2
STOCKHOLDERS' EQUITY
Common Stock	408.6	408.6
Additional Paid-In Capital	983.5	1,009.6
Retained Earnings	14,278.9	14,233.8
Accumulated Other Comprehensive Loss	(917.6)	(1,137.9)
Treasury Stock	(3,536.5)	(3,501.1)
Total Stockholders’ Equity	12,101.8	11,897.9
Total Liabilities and Stockholders’ Equity	156,111	150,783.1
Series D Preferred Stock
STOCKHOLDERS' EQUITY
Preferred Stock	493.5	493.5
Series E Preferred Stock
STOCKHOLDERS' EQUITY
Preferred Stock	391.4	391.4
Commercial
Loans
Total Loans (Net of unearned income of $6.6 and $5.9)	25,417.1	25,412.8
Personal
Loans
Total Loans (Net of unearned income of $6.6 and $5.9)	$ 21,925.5	$ 22,204.2

Consolidated Balance Sheets (_2

Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Available-for-sale securities, amortized cost	$ 25,941.9	$ 23,659
Held to maturity, fair value	21,641.4	24,473
Unearned income	$ 6.6	$ 5.9
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Common stock, par value (in dollars per share)	$ 1.6667	$ 1.6667
Common stock, authorized (in shares)	560,000,000	560,000,000
Common stock, outstanding (in shares)	204,591,724	205,126,224
Treasury stock, (in shares)	40,579,800	40,045,300
Series D Preferred Stock
Preferred stock, outstanding (in shares)	5,000	5,000
Series E Preferred Stock
Preferred stock, outstanding (in shares)	16,000	16,000

Consolidated Statements of Inco

Consolidated Statements of Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,142.9	$ 1,063.6
Foreign Exchange Trading Income	57	53
Treasury Management Fees	9.3	8.4
Security Commissions and Trading Income	37.9	34.7
Other Operating Income	61	46.8
Investment Security Gains (Losses), net	(189.4)	6.9
Total Noninterest Income	1,118.7	1,213.4
Net Interest Income
Interest Income	2,445.6	1,455.4
Interest Expense	1,917.5	924.2
Net Interest Income	528.1	531.2
Provision for Credit Losses	(8.5)	15
Net Interest Income after Provision for Credit Losses	536.6	516.2
Noninterest Expense
Compensation	627.1	595.2
Employee Benefits	101.1	101
Outside Services	229.3	210.8
Equipment and Software	252.7	231.7
Occupancy	54.1	61.3
Other Operating Expense	100.4	85.6
Total Noninterest Expense	1,364.7	1,285.6
Income before Income Taxes	290.6	444
Provision for Income Taxes	75.9	109.4
Net Income	214.7	334.6
Preferred Stock Dividends	16.2	16.2
Net Income Applicable to Common Stock	$ 198.5	$ 318.4
Per Common Share
Net Income — Basic (in dollars per share)	$ 0.96	$ 1.51
Net Income - Diluted (in dollars per share)	$ 0.96	$ 1.51
Average Number of Common Shares Outstanding
Basic (in shares)	204,628,796	208,186,841
Diluted (in shares)	205,134,845	208,730,389

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net Income	$ 214.7	$ 334.6
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Available for Sale Debt Securities	213.4	180.2
Net Unrealized Gains (Losses) on Cash Flow Hedges	(0.7)	(0.1)
Net Foreign Currency Adjustments	4.6	22.7
Net Pension and Other Postretirement Benefit Adjustments	3	0.2
Net Change	220.3	203
Comprehensive Income (Loss)	$ 435	$ 537.6

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) $ in Millions	Total	PREFERRED STOCK	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	TREASURY STOCK
Beginning balance at Dec. 31, 2022	$ 11,259.5	$ 884.9	$ 408.6	$ 983.5	$ 13,798.5	$ (1,569.2)	$ (3,246.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	334.6				334.6
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	203					203
Dividends Declared:
Common Stock	(158.6)				(158.6)
Preferred Stock	(16.2)				(16.2)
Stock Awards and Options Exercised	66.4			(19)			85.4
Stock Purchased	(100.9)						(100.9)
Ending balance at Mar. 31, 2023	11,587.8	884.9	408.6	964.5	13,958.3	(1,366.2)	(3,262.3)
Beginning balance at Dec. 31, 2023	11,897.9	884.9	408.6	1,009.6	14,233.8	(1,137.9)	(3,501.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	214.7				214.7
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	220.3					220.3
Dividends Declared:
Common Stock	(153.4)				(153.4)
Preferred Stock	(16.2)				(16.2)
Stock Awards and Options Exercised	71			(26.1)			97.1
Stock Purchased	(132)						(132)
Excise Tax on Share Repurchases	(0.5)						(0.5)
Ending balance at Mar. 31, 2024	$ 12,101.8	$ 884.9	$ 408.6	$ 983.5	$ 14,278.9	$ (917.6)	$ (3,536.5)

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Statement of Stockholders' Equity [Abstract]
Common stock dividends (in usd per share)	$ 0.75	$ 0.75

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income		$ 214.7	$ 334.6
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Investment Security Losses/(Gains)		189.4	(6.9)
Amortization and Accretion of Securities and Unearned Income, net		(7.7)	7
Provision for Credit Losses		(8.5)	15
Depreciation and Amortization		170.3	154.9
Pension Plan Contributions		(208)	(16.5)
Change in Receivables		(173.4)	(193.1)
Change in Interest Payable		56.4	59.8
Change in Collateral With Derivative Counterparties, net		(1,118)	(717.8)
Other Operating Activities, net		(567.8)	198.1
Net Cash Used in Operating Activities		(1,452.6)	(164.9)
CASH FLOWS FROM INVESTING ACTIVITIES
Change in Securities Purchased under Agreements to Resell		251.9	36.4
Change in Interest-Bearing Deposits with Banks		523.3	360
Net Change in Federal Reserve and Other Central Bank Deposits		(6,267.8)	1,021.6
Purchases of Held to Maturity Debt Securities		(6,134.3)	(9,867.8)
Proceeds from the Maturity and Redemption of Held to Maturity Debt Securities		8,606.3	10,412.9
Purchases of Available for Sale Debt Securities		(5,537.5)	(1,273.9)
Proceeds from the Maturity and Sales of Available for Sale Debt Securities		2,894.5	3,626.5
Change in Loans		253.7	528.9
Purchases of Buildings and Equipment		(14.3)	(11.5)
Purchases and Development of Computer Software		(113.5)	(117.6)
Change in Client Security Settlement Receivables		90.7	400.2
Other Investing Activities, net		653.6	(196.5)
Net Cash (Used in) / Provided by Investing Activities		(4,793.4)	4,919.2
CASH FLOWS FROM FINANCING ACTIVITIES
Change in Deposits		7,982.9	(10,478.1)
Change in Federal Funds Purchased		(445)	2,590.4
Change in Securities Sold under Agreements to Repurchase		(273.3)	(204.3)
Change in Short-Term Other Borrowings		(30.5)	3,766.3
Treasury Stock Purchased		(132)	(100.9)
Net Proceeds from Stock Options		4.1	1.6
Cash Dividends Paid on Common Stock		(153.6)	(156.5)
Cash Dividends Paid on Preferred Stock		(16.2)	(16.2)
Other Financing Activities, net		(0.4)	0
Net Cash Provided by / (Used in) Financing Activities		6,936	(4,597.7)
Effect of Foreign Currency Exchange Rates on Cash		(172.8)	15.1
Change in Cash and Due from Banks		517.2	171.7
Cash and Due from Banks at Beginning of Period		4,791.5	4,654.2
Cash and Due from Banks at End of Period		5,308.7	4,825.9
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest Paid		1,857	864.1
Income Taxes Paid		39.3	31.2
Reclassification of certain cash collateral received from Other Operating Activities to Deposits (1)	[1]	$ 765.3	$ 0
[1]Beginning January 1, 2024, Northern Trust reclassified certain cash collateral received from Other Liabilities to Deposits on the consolidated statement of financial condition. Prior periods have not been restated.

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of Northern Trust Corporation (Corporation) and its wholly-owned subsidiary, The Northern Trust Company (Bank), and various other wholly-owned subsidiaries of the Corporation and Bank. Throughout the notes to the consolidated financial statements, the term “Northern Trust” refers to the Corporation and its subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements, as of and for the periods ended March 31, 2024 and 2023, have not been audited by the Corporation’s independent registered public accounting firm. In the opinion of management, all accounting entries and adjustments, including normal recurring accruals, necessary for a fair presentation of the financial position and the results of operations for the interim periods have been made. The accounting and financial reporting policies of Northern Trust conform to U.S. generally accepted accounting principles (GAAP) and reporting practices prescribed for the banking industry. For a description of Northern Trust’s significant accounting policies, refer to Note 1—Summary of Significant Accounting Policies included under Item 8. Financial Statements and Supplementary Data in the Annual Report on Form 10-K for the year ended December 31, 2023.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2024
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements On January 1, 2024, Northern Trust adopted Accounting Standards Update (ASU) No. 2023-02, “Investments—Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Tax Credit Structures Using the Proportional Amortization Method—a consensus of the Emerging Issues Task Force” (ASU 2023-02). The amendments in ASU 2023-02 allow entities to elect the proportional amortization method to account for tax equity investments if certain conditions are met regardless of the tax credit program from which the income tax credits are received. Under the proportional amortization method, an entity amortizes the initial cost of the investment in proportion to the income tax credits and other income tax benefits received and recognizes the net amortization and income tax credits and other income tax benefits in the income statement as a component of income tax expense (benefit). In addition, ASU 2023-02 requires specific disclosures that must be applied to all investments that generate income tax credits and other income tax benefits for which the entity has elected to apply the proportional amortization method in accordance with Subtopic 323-740. Upon adoption of ASU 2023-02, there was no significant impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. Please refer to Note 19—Variable Interest Entities for further information. On January 1, 2024, Northern Trust adopted ASU No. 2022-03, “Fair Value Measurement (Topic 820): Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions” (ASU 2022-03). The amendments in ASU 2022-03 clarify that a contractual restriction on the sale of an equity security is not considered part of the unit of account of the equity security and, therefore, is not considered in measuring fair value. ASU 2022-03 also clarifies that an entity cannot, as a separate unit of account, recognize and measure a contractual sale restriction. Additionally, ASU 2022-03 introduces new disclosure requirements to provide investors with information about contractual sale restrictions including the nature and remaining duration of these restrictions. Upon adoption of ASU 2022-03, there was no impact to Northern Trust’s consolidated balance sheets or consolidated statements of income.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair Value Hierarchy. The following describes the hierarchy of valuation inputs (Levels 1, 2, and 3) used to measure fair value and the primary valuation methodologies used by Northern Trust for financial instruments measured at fair value on a recurring basis. Observable inputs reflect market data obtained from sources independent of the reporting entity; unobservable inputs reflect the entity’s own assumptions about how market participants would value an asset or liability based on the best information available. GAAP requires an entity measuring fair value to maximize the use of observable inputs and minimize the use of unobservable inputs and establishes a fair value hierarchy of inputs. Financial instruments are categorized within the hierarchy based on the lowest level input that is significant to their valuation. No transfers into or out of Level 3 occurred during the three months ended March 31, 2024 or the year ended December 31, 2023. Level 1 — Quoted, active market prices for identical assets or liabilities. Northern Trust’s Level 1 assets are comprised primarily of available for sale (AFS) investments in U.S. Treasury securities. Level 2 — Observable inputs other than Level 1 prices, such as quoted active market prices for similar assets or liabilities, quoted prices for identical or similar assets in inactive markets, and model-derived valuations in which all significant inputs are observable in active markets. Northern Trust’s Level 2 assets include AFS and certain trading account debt securities, the fair values of which are determined predominantly by external pricing vendors. Prices received from vendors are compared to other vendor and third-party prices. If a security price obtained from a pricing vendor is determined to exceed predetermined tolerance levels that are assigned based on an asset type’s characteristics, the exception is researched and, if the price is not able to be validated, an alternate pricing vendor is utilized, consistent with Northern Trust’s pricing source hierarchy. As of March 31, 2024, Northern Trust’s AFS debt securities portfolio included 910 Level 2 debt securities with an aggregate market value of $19.5 billion. Substantially all were valued by external pricing vendors. As of December 31, 2023, Northern Trust’s AFS debt securities portfolio included 929 Level 2 debt securities with an aggregate market value of $19.5 billion. All 929 debt securities were valued by external pricing vendors. Level 2 assets and liabilities also include derivative contracts which are valued internally using widely accepted income-based models that incorporate inputs readily observable in actively quoted markets and reflect the contractual terms of the contracts. Observable inputs include foreign exchange rates and interest rates for foreign exchange contracts; interest rates for interest rate swap contracts and forward contracts; and interest rates and volatility inputs for interest rate option contracts. Northern Trust evaluates the impact of counterparty credit risk and its own credit risk on the valuation of its derivative instruments. Factors considered include the likelihood of default by Northern Trust and its counterparties, the remaining maturities of the instruments, net exposures after giving effect to master netting arrangements or similar agreements, available collateral, and other credit enhancements in determining the appropriate fair value of derivative instruments. The resulting valuation adjustments have not been considered material. Level 3 — Valuation techniques in which one or more significant inputs are unobservable in the marketplace. Northern Trust’s Level 3 liabilities consist of swaps that Northern Trust entered into with the purchaser of 1.1 million and 1.0 million shares of Visa Inc. Class B common stock (Visa Class B common shares) previously held by Northern Trust and sold in June 2016 and 2015, respectively. Pursuant to the swaps, Northern Trust retains the risks associated with the ultimate conversion of the Visa Class B common shares into shares of Visa Inc. Class A common stock (Visa Class A common shares), such that the counterparty will be compensated for any dilutive adjustments to the conversion ratio and Northern Trust will be compensated for any anti-dilutive adjustments to the ratio. The swaps also require periodic payments from Northern Trust to the counterparty calculated by reference to the market price of Visa Class A common shares and a fixed rate of interest. The fair value of the swaps is determined using a discounted cash flow methodology. The significant unobservable inputs used in the fair value measurement are Northern Trust’s own assumptions about estimated changes in the conversion rate of the Visa Class B common shares into Visa Class A common shares, the date on which such conversion is expected to occur and the estimated growth rate of the Visa Class A common share price. See “Visa Class B Common Shares” under Note 20—Commitments and Contingent Liabilities for further information. Northern Trust believes its valuation methods for its assets and liabilities carried at fair value are appropriate; however, the use of different methodologies or assumptions, particularly as applied to Level 3 assets and liabilities, could have a material effect on the computation of their estimated fair values. The following table presents the fair values of Northern Trust’s Level 3 liabilities as of March 31, 2024 and December 31, 2023, as well as the valuation techniques, significant unobservable inputs, and quantitative information used to develop significant unobservable inputs for such liabilities as of such dates. TABLE 30: LEVEL 3 SIGNIFICANT UNOBSERVABLE INPUTS MARCH 31, 2024 FINANCIAL INSTRUMENT FAIR VALUE VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES (1) Swaps Related to Sale of Certain Visa Class B Common Shares $21.0 million Discounted Cash Flow Conversion Rate 1.59x 1.59x Visa Class A Appreciation 9.22% 9.22% Expected Duration 6 - 24 months 10 months (1) Weighted average of expected duration based on scenario probability. DECEMBER 31, 2023 FINANCIAL INSTRUMENT FAIR VALUE VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES (1) Swaps Related to Sale of Certain Visa Class B Common Shares $25.4 million Discounted Cash Flow Conversion Rate 1.59x 1.59x Visa Class A Appreciation 10.49% 10.49% Expected Duration 9 - 27 months 13 months (1) Weighted average of expected duration based on scenario probability. The following table presents assets and liabilities measured at fair value on a recurring basis as of March 31, 2024 and December 31, 2023, segregated by fair value hierarchy level. TABLE 31: RECURRING BASIS HIERARCHY LEVELING MARCH 31, 2024 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 6,112.3 $ — $ — $ — $ 6,112.3 Obligations of States and Political Subdivisions — 295.0 — — 295.0 Government Sponsored Agency — 12,351.4 — — 12,351.4 Non-U.S. Government — 307.6 — — 307.6 Corporate Debt — 250.2 — — 250.2 Covered Bonds — 296.8 — — 296.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,860.8 — — 2,860.8 Other Asset-Backed — 2,523.0 — — 2,523.0 Commercial Mortgage-Backed — 641.8 — — 641.8 Total Available for Sale Debt Securities 6,112.3 19,526.6 — — 25,638.9 Other Assets Money Market Investment 95.0 — — — 95.0 Derivative Assets Foreign Exchange Contracts — 1,357.1 — (699.0) 658.1 Interest Rate Contracts — 404.0 — (215.2) 188.8 Total Derivative Assets — 1,761.1 — (914.2) 846.9 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 1,318.1 — (1,051.2) 266.9 Interest Rate Contracts — 477.9 — (2.7) 475.2 Other Financial Derivatives (1) — — 21.0 (16.2) 4.8 Total Derivative Liabilities $ — $ 1,796.0 $ 21.0 $ (1,070.1) $ 746.9 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of March 31, 2024, derivative assets and liabilities shown above also include reductions of $181.0 million and $336.9 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties. DECEMBER 31, 2023 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 3,622.2 $ — $ — $ — $ 3,622.2 Obligations of States and Political Subdivisions — 295.8 — — 295.8 Government Sponsored Agency — 11,553.0 — — 11,553.0 Non-U.S. Government — 264.4 — — 264.4 Corporate Debt — 279.5 — — 279.5 Covered Bonds — 347.1 — — 347.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,899.9 — — 2,899.9 Other Asset-Backed — 2,962.6 — — 2,962.6 Commercial Mortgage-Backed — 865.3 — — 865.3 Total Available for Sale 3,622.2 19,467.6 — — 23,089.8 Trading Account — — — — — Total Available for Sale Debt Securities 3,622.2 19,467.6 — — 23,089.8 Other Assets Money Market Investment 95.0 — — — 95.0 Derivative Assets Foreign Exchange Contracts — 3,266.7 — (2,937.2) 329.5 Interest Rate Contracts — 301.5 — (189.5) 112.0 Total Derivative Assets — 3,568.2 — (3,126.7) 441.5 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 3,255.2 — (2,175.7) 1,079.5 Interest Rate Contracts — 369.2 — (6.0) 363.2 Other Financial Derivatives (1) — — 25.4 (23.7) 1.7 Total Derivative Liabilities $ — $ 3,624.4 $ 25.4 $ (2,205.4) $ 1,444.4 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of December 31, 2023, derivative assets and liabilities shown above also include reductions of $2,093.8 million and $1,172.5 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1) Consists of swaps related to the sale of certain Visa Class B common shares. The following table presents the changes in Level 3 liabilities for the three months ended March 31, 2024 and 2023. TABLE 32: CHANGES IN LEVEL 3 LIABILITIES (In Millions) SWAPS RELATED TO SALE OF CERTAIN VISA CLASS B COMMON SHARES THREE MONTHS ENDED MARCH 31, 2024 2023 Fair Value at January 1 $ 25.4 $ 34.8 Total (Gains) Losses: Included in Earnings (1) 1.2 7.6 Purchases, Issues, Sales, and Settlements Settlements (5.5) (7.8) Fair Value at March 31 $ 21.1 $ 34.6 (1) (Gains) losses are recorded in Other Operating Income on the consolidated statements of income. Carrying values of assets and liabilities that are not measured at fair value on a recurring basis may be adjusted to fair value in periods subsequent to their initial recognition, for example, to record an impairment of an asset. GAAP requires entities to separately disclose these subsequent fair value measurements and to classify them under the fair value hierarchy. Assets measured at fair value on a nonrecurring basis at March 31, 2024 and December 31, 2023, all of which were categorized as Level 3 under the fair value hierarchy, were comprised of nonaccrual loans whose values were based on real estate and other available collateral, and of other real estate owned (OREO) properties. Fair values of real estate loan collateral were estimated using a market approach typically supported by third-party valuations and property-specific fees and taxes. The fair values of real estate loan collateral are subject to adjustments to reflect management’s judgment as to realizable value. The fair value of collateral-dependent nonaccrual loans totaled $0.1 million at March 31, 2024. Due to immateriality, management did not apply a discount factor to the balance as of March 31, 2024. Collateral-dependent nonaccrual loans that have been adjusted to fair value totaled $43.3 million at December 31, 2023. Management adjustments consisted of a range of discount factors from 0.0% to 20.0% with a weighted average of 2.0% as of December 31, 2023. Other loan collateral, which typically consists of accounts receivable, inventory and equipment, is valued using a market approach adjusted for asset-specific characteristics and in limited instances third-party valuations are used. OREO assets are carried at the lower of cost or fair value less estimated costs to sell, with fair value typically based on third-party appraisals. The following table presents the fair values of Northern Trust’s Level 3 assets that were measured at fair value on a nonrecurring basis as of March 31, 2024 and December 31, 2023, as well as the valuation technique, significant unobservable inputs and quantitative information used to develop the significant unobservable inputs for such assets as of such dates. TABLE 33: LEVEL 3 NONRECURRING BASIS SIGNIFICANT UNOBSERVABLE INPUTS MARCH 31, 2024 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $0.1 million Market Approach Discount factor applied to real estate collateral-dependent loans to reflect realizable value N/A N/A (1) Includes real estate collateral-dependent loans and other collateral-dependent loans. DECEMBER 31, 2023 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $43.3 million Market Approach Discount factor applied to real estate collateral-dependent loans to reflect realizable value 0.0 % - 20.0% 2.0% (1) Includes real estate collateral-dependent loans and other collateral-dependent loans. The following tables present the book value and estimated fair value, including the fair value hierarchy level, of Northern Trust’s financial instruments that are not measured at fair value on the consolidated balance sheets as of March 31, 2024 and December 31, 2023. The following tables exclude those items measured at fair value on a recurring basis. TABLE 34: FAIR VALUE OF FINANCIAL INSTRUMENTS MARCH 31, 2024 ESTIMATED FAIR VALUE (In Millions) BOOK VALUE TOTAL ESTIMATED FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 FINANCIAL ASSETS Cash and Due from Banks $ 5,308.7 $ 5,308.7 $ 5,308.7 $ — $ — Federal Reserve and Other Central Bank Deposits 40,269.9 40,269.9 — 40,269.9 — Interest-Bearing Deposits with Banks 1,372.1 1,372.1 — 1,372.1 — Securities Purchased under Agreements to Resell 500.1 500.1 — 500.1 — Debt Securities - Held to Maturity 23,497.9 21,641.4 — 21,641.4 — Loans Held for Investment 47,180.1 47,179.4 — — 47,179.4 Other Assets 1,505.7 1,490.3 95.2 1,395.1 — FINANCIAL LIABILITIES Deposits 123,941.7 123,996.6 — 123,996.6 — Federal Funds Purchased 2,600.5 2,600.5 — 2,600.5 — Securities Sold Under Agreements to Repurchase 511.4 511.4 — 511.4 — Other Borrowings 6,526.2 6,544.3 — 6,544.3 — Senior Notes 2,743.5 2,771.3 — 2,771.3 — Long-Term Debt 4,069.0 4,135.7 — 4,135.7 — Unfunded Commitments 163.3 163.3 — 163.3 — Other Liabilities 42.7 42.7 — — 42.7 DECEMBER 31, 2023 ESTIMATED FAIR VALUE (In Millions) BOOK VALUE TOTAL ESTIMATED FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 FINANCIAL ASSETS Cash and Due from Banks $ 4,791.5 $ 4,791.5 $ 4,791.5 $ — $ — Federal Reserve and Other Central Bank Deposits 34,326.2 34,326.2 — 34,326.2 — Interest-Bearing Deposits with Banks 1,939.0 1,939.0 — 1,939.0 — Securities Purchased under Agreements to Resell 784.7 784.7 — 784.7 — Debt Securities - Held to Maturity 26,221.7 24,473.0 — 24,473.0 — Loans Held for Investment 47,438.3 47,598.3 — — 47,598.3 Other Assets 1,476.6 1,458.0 86.1 1,371.9 — FINANCIAL LIABILITIES Deposits 116,164.0 116,207.6 — 116,207.6 — Federal Funds Purchased 3,045.4 3,045.4 — 3,045.4 — Securities Sold Under Agreements to Repurchase 784.7 784.7 — 784.7 — Other Borrowings 6,567.8 6,607.4 — 6,607.4 — Senior Notes 2,773.2 2,798.1 — 2,798.1 — Long-Term Debt 4,065.0 4,186.8 — 4,186.8 — Unfunded Commitments 178.8 178.8 — 178.8 — Other Liabilities 74.9 74.9 — — 74.9

Securities

Securities	3 Months Ended
	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Securities	Securities Available for Sale Debt Securities. The following tables provide the amortized cost and fair values as of March 31, 2024 and December 31, 2023, and remaining maturities of AFS debt securities as of March 31, 2024. TABLE 35: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF AVAILABLE FOR SALE DEBT SECURITIES MARCH 31, 2024 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 6,121.6 $ 11.0 $ 20.3 $ 6,112.3 Obligations of States and Political Subdivisions 309.6 — 14.6 295.0 Government Sponsored Agency 12,501.9 12.5 163.0 12,351.4 Non-U.S. Government 325.0 0.1 17.5 307.6 Corporate Debt 256.5 0.2 6.5 250.2 Covered Bonds 302.7 0.3 6.2 296.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,912.6 3.8 55.6 2,860.8 Other Asset-Backed 2,552.4 1.6 31.0 2,523.0 Commercial Mortgage-Backed 659.6 0.2 18.0 641.8 Total $ 25,941.9 $ 29.7 $ 332.7 $ 25,638.9 DECEMBER 31, 2023 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 3,681.5 $ 2.2 $ 61.5 $ 3,622.2 Obligations of States and Political Subdivisions 315.8 — 20.0 295.8 Government Sponsored Agency 11,744.3 9.0 200.3 11,553.0 Non-U.S. Government 284.8 — 20.4 264.4 Corporate Debt 287.5 0.1 8.1 279.5 Covered Bonds 356.8 — 9.7 347.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,013.8 0.1 114.0 2,899.9 Other Asset-Backed 3,061.0 1.6 100.0 2,962.6 Commercial Mortgage-Backed 913.5 0.2 48.4 865.3 Total $ 23,659.0 $ 13.2 $ 582.4 $ 23,089.8 TABLE 36: REMAINING MATURITY OF AVAILABLE FOR SALE DEBT SECURITIES MARCH 31, 2024 ONE YEAR OR LESS ONE TO FIVE YEARS FIVE TO TEN YEARS OVER TEN YEARS TOTAL (In Millions) AMORTIZED COST FAIR VALUE AMORTIZED COST FAIR VALUE AMORTIZED COST FAIR VALUE AMORTIZED COST FAIR VALUE AMORTIZED COST FAIR VALUE U.S. Government $ 348.1 $ 344.2 $ 3,422.0 $ 3,412.9 $ 2,351.5 $ 2,355.2 $ — $ — $ 6,121.6 $ 6,112.3 Obligations of States and Political Subdivisions — — 111.2 106.5 198.4 188.5 — — 309.6 295.0 Government Sponsored Agency 2,631.6 2,606.9 5,460.5 5,396.1 3,409.8 3,375.2 1,000.0 973.2 12,501.9 12,351.4 Non-U.S. Government 64.8 63.5 260.2 244.1 — — — — 325.0 307.6 Corporate Debt 103.1 102.3 153.4 147.9 — — — — 256.5 250.2 Covered Bonds 66.4 65.9 236.3 230.9 — — — — 302.7 296.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 126.8 125.4 2,564.7 2,525.9 221.1 209.5 — — 2,912.6 2,860.8 Other Asset-Backed 218.3 213.5 2,108.8 2,083.8 122.7 123.0 102.6 102.7 2,552.4 2,523.0 Commercial Mortgage-Backed 21.7 20.6 577.1 570.2 60.8 51.0 — — 659.6 641.8 Total $ 3,580.8 $ 3,542.3 $ 14,894.2 $ 14,718.3 $ 6,364.3 $ 6,302.4 $ 1,102.6 $ 1,075.9 $ 25,941.9 $ 25,638.9 Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments. Available for Sale Debt Securities with Unrealized Losses. The following table provides information regarding AFS debt securities with no credit losses reported that had been in a continuous unrealized loss position for less than twelve months and for twelve months or longer as of March 31, 2024 and December 31, 2023. TABLE 37: AVAILABLE FOR SALE DEBT SECURITIES IN UNREALIZED LOSS POSITION WITH NO CREDIT LOSSES REPORTED MARCH 31, 2024 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ 87.4 $ 12.0 $ 819.5 $ 8.3 $ 906.9 $ 20.3 Obligations of States and Political Subdivisions 295.0 14.6 — — 295.0 14.6 Government Sponsored Agency 145.3 7.9 8,865.2 155.1 9,010.5 163.0 Non-U.S. Government 63.5 1.3 189.5 16.2 253.0 17.5 Corporate Debt 36.9 0.9 55.7 0.9 92.6 1.8 Covered Bonds 60.4 0.5 104.9 5.7 165.3 6.2 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 110.0 5.0 1,066.0 50.6 1,176.0 55.6 Other Asset-Backed 13.9 0.7 995.0 30.3 1,008.9 31.0 Commercial Mortgage-Backed 6.0 0.4 607.4 17.6 613.4 18.0 Total $ 818.4 $ 43.3 $ 12,703.2 $ 284.7 $ 13,521.6 $ 328.0 Note: Two corporate debt AFS securities with a fair value of $80.1 million and unrealized losses of $4.7 million have been excluded from the table above as these AFS securities have a $0.5 million allowance for credit losses reported as of March 31, 2024. Refer to the discussion further below and Note 6—Allowance for Credit Losses for further information. DECEMBER 31, 2023 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ — $ — $ 3,364.7 $ 61.5 $ 3,364.7 $ 61.5 Obligations of States and Political Subdivisions 87.8 5.9 208.0 14.1 295.8 20.0 Government Sponsored Agency 331.0 11.5 9,486.6 188.8 9,817.6 200.3 Non-U.S. Government — — 264.5 20.4 264.5 20.4 Corporate Debt 4.4 0.1 143.0 2.1 147.4 2.2 Covered Bonds — — 213.2 9.7 213.2 9.7 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — — 2,477.0 105.8 2,477.0 105.8 Other Asset-Backed 19.8 2.0 1,998.7 98.0 2,018.5 100.0 Commercial Mortgage-Backed 60.0 4.6 776.6 43.8 836.6 48.4 Total $ 503.0 $ 24.1 $ 18,932.3 $ 544.2 $ 19,435.3 $ 568.3 Note: Three corporate debt AFS securities with a fair value of $98.4 million and unrealized losses of $5.9 million and one sub-sovereign, supranational and non-U.S. agency bonds AFS security with a fair value of $71.0 million and unrealized loss of $8.2 million have been excluded from the table above as these AFS securities have a $1.2 million allowance for credit losses reported as of December 31, 2023. Refer to the discussion further below and Note 6—Allowance for Credit Losses for further information. As of March 31, 2024, 784 AFS debt securities with a combined fair value of $13.5 billion were in an unrealized loss position without an allowance for credit losses, with their unrealized losses totaling $328.0 million. As of March 31, 2024, unrealized losses related to AFS debt securities of $163.0 million, $55.6 million, and $31.0 million related to government-sponsored agency securities, sub-sovereign, supranational and non-U.S. agency bonds and other asset-backed, respectively, which are primarily attributable to higher intermediate rates. As of December 31, 2023, 898 AFS debt securities with a combined fair value of $19.4 billion were in an unrealized loss position without an allowance for credit losses, with their unrealized losses totaling $568.3 million. As of December 31, 2023, unrealized losses related to AFS debt securities of $200.3 million, $105.8 million, and $100.0 million related to government-sponsored agency, sub-sovereign, supranational and non-U.S. agency bonds, and other asset-backed, respectively, which are primarily attributable to lower yields and tighter spreads. AFS debt securities impairment reviews are conducted quarterly to identify and evaluate securities that have indications of possible credit losses. A determination as to whether a security’s decline in market value is related to credit impairment takes into consideration numerous factors and the relative significance of any single factor can vary by security. Factors Northern Trust considers in determining whether impairment is credit-related include, but are not limited to, the severity of the impairment; the cause of the impairment; the financial condition and near-term prospects of the issuer; activity in the market of the issuer, which may indicate adverse credit conditions; Northern Trust’s intent regarding the sale of the security as of the balance sheet date; and the likelihood that Northern Trust will not be required to sell the security for a period of time sufficient to allow for the recovery of the security’s amortized cost basis. For each security meeting the requirements of Northern Trust’s internal screening process, an extensive review is conducted to determine if a credit loss has occurred. In January 2024, the Corporation sold certain AFS debt securities that were in an unrealized loss position. The $189.4 million loss is recognized in Investment Security Gains (Losses), net on the consolidated statements of income for the period ended March 31, 2024. In November 2023, the Corporation sold certain AFS debt securities that were in an unrealized loss position. The $176.4 million loss is recognized in Investment Security Gains (Losses), net on the consolidated statements of income for the period ended December 31, 2023. There was a $0.7 million negative Provision for Credit Losses for AFS securities for the three months ended March 31, 2024. There was a $0.5 million Provision for Credit Losses for AFS securities for the three months ended March 31, 2023. There was a $0.5 million allowance for credit losses for AFS securities as of March 31, 2024 which was related to corporate debt securities and $1.2 million allowance for credit losses for AFS securities as of December 31, 2023, which was related to corporate debt securities and non-U.S. agency bonds. The process for identifying credit losses for AFS securities is based on the best estimate of cash flows to be collected from the security, discounted using the security’s effective interest rate. If the present value of the expected cash flows is found to be less than the current amortized cost of the security, an allowance for credit losses is generally recorded equal to the difference between the two amounts, limited to the amount the amortized cost basis exceeds the fair value of the security. For additional information, please refer to Note 6— Allowance for Credit Losses. Held to Maturity Debt Securities. Held to maturity (HTM) debt securities consist of securities that management intends to, and Northern Trust has the ability to, hold until maturity. The following tables provide the amortized cost and fair values as of March 31, 2024 and December 31, 2023, and remaining maturities of HTM debt securities as of March 31, 2024. TABLE 38: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF HELD TO MATURITY DEBT SECURITIES MARCH 31, 2024 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR Obligations of States and Political Subdivisions $ 2,571.6 $ 0.3 $ 89.5 $ 2,482.4 Government Sponsored Agency 9,223.3 1.6 1,099.2 8,125.7 Non-U.S. Government 2,742.1 0.1 92.3 2,649.9 Corporate Debt 610.3 — 24.7 585.6 Covered Bonds 2,110.3 0.7 103.8 2,007.2 Certificates of Deposit 403.2 — 0.2 403.0 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 5,024.5 1.6 289.4 4,736.7 Other Asset-Backed 193.7 1.3 0.2 194.8 Commercial Mortgage-Backed 37.6 — 0.3 37.3 Other 581.3 — 162.5 418.8 Total $ 23,497.9 $ 5.6 $ 1,862.1 $ 21,641.4 DECEMBER 31, 2023 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR Obligations of States and Political Subdivisions 2,563.9 0.5 72.4 2,492.0 Government Sponsored Agency 9,355.3 2.3 1,012.4 8,345.2 Non-U.S. Government 4,789.1 0.2 90.7 4,698.6 Corporate Debt 646.1 — 28.2 617.9 Covered Bonds 2,208.6 0.3 108.3 2,100.6 Certificates of Deposit 585.1 — 0.7 584.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 5,245.5 3.2 294.9 4,953.8 Other Asset-Backed 214.2 0.4 0.2 214.4 Commercial Mortgage-Backed 37.6 — 0.8 36.8 Other 576.3 — 147.0 429.3 Total $ 26,221.7 $ 6.9 $ 1,755.6 $ 24,473.0 As of March 31, 2024, the $23.5 billion HTM debt securities portfolio had unrealized losses of $1.1 billion and $289.4 million related to government-sponsored agency and sub-sovereign, supranational and non-U.S. agency bonds, respectively, which are primarily attributable to higher intermediate rates. As of December 31, 2023, the $26.2 billion HTM debt securities portfolio had unrealized losses of $1.0 billion and $294.9 million related to government-sponsored agency and sub-sovereign, supranational and non-U.S. agency bonds, respectively, which are primarily attributable to lower yields and tighter spreads. TABLE 39: REMAINING MATURITY OF HELD TO MATURITY DEBT SECURITIES MARCH 31, 2024 ONE YEAR OR LESS ONE TO FIVE YEARS FIVE TO TEN YEARS OVER TEN YEARS TOTAL (In Millions) Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Obligations of States and Political Subdivisions $ 60.4 $ 60.0 $ 1,206.8 $ 1,174.1 $ 1,039.9 $ 998.1 $ 264.5 $ 250.2 $ 2,571.6 $ 2,482.4 Government Sponsored Agency 990.3 883.6 3,419.8 3,038.5 3,138.9 2,768.6 1,674.3 1,435.0 9,223.3 8,125.7 Non-U.S. Government 1,569.9 1,564.7 1,139.3 1,056.5 32.9 28.7 — — 2,742.1 2,649.9 Corporate Debt 247.8 243.0 347.3 329.8 15.2 12.8 — — 610.3 585.6 Covered Bonds 493.8 492.7 1,389.9 1,310.4 226.6 204.1 — — 2,110.3 2,007.2 Certificates of Deposit 403.2 403.0 — — — — — — 403.2 403.0 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 1,058.4 1,035.1 3,960.5 3,697.1 5.6 4.5 — — 5,024.5 4,736.7 Other Asset-Backed 1.2 1.2 120.7 121.5 71.8 72.1 — — 193.7 194.8 Commercial Mortgage-Backed — — 37.6 37.3 — — — — 37.6 37.3 Other 50.7 49.2 319.8 285.0 33.1 24.9 177.7 59.7 581.3 418.8 Total $ 4,875.7 $ 4,732.5 $ 11,941.7 $ 11,050.2 $ 4,564.0 $ 4,113.8 $ 2,116.5 $ 1,744.9 $ 23,497.9 $ 21,641.4 Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments. Credit Quality Indicators. The following table provides the amortized cost of HTM debt securities by credit rating. TABLE 40: AMORTIZED COST OF HELD TO MATURITY DEBT SECURITIES BY CREDIT RATING MARCH 31, 2024 ($ In Millions) AAA AA A BBB NOT RATED TOTAL Obligations of States and Political Subdivisions $ 956.9 $ 1,614.7 $ — $ — $ — $ 2,571.6 Government Sponsored Agency 9,223.3 — — — — 9,223.3 Non-U.S. Government 896.7 707.4 812.9 325.1 — 2,742.1 Corporate Debt 2.2 298.7 309.4 — — 610.3 Covered Bonds 2,110.3 — — — — 2,110.3 Certificates of Deposit 355.4 — — — 47.8 403.2 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,840.8 1,153.1 29.5 1.1 — 5,024.5 Other Asset-Backed 193.7 — — — — 193.7 Commercial Mortgage-Backed 37.6 — — — — 37.6 Other 52.5 — — — 528.8 581.3 Total $ 17,669.4 $ 3,773.9 $ 1,151.8 $ 326.2 $ 576.6 $ 23,497.9 Percent of Total 75 % 16 % 5 % 1 % 3 % 100 % DECEMBER 31, 2023 ($ In Millions) AAA AA A BBB NOT RATED TOTAL U.S. Government $ — $ — $ — $ — $ — $ — Obligations of States and Political Subdivisions 954.7 1,609.0 — — 0.2 2,563.9 Government Sponsored Agency 9,355.3 — — — — 9,355.3 Non-U.S. Government 813.3 1,179.6 2,463.3 332.9 — 4,789.1 Corporate Debt 2.1 302.6 341.4 — — 646.1 Covered Bonds 2,208.6 — — — — 2,208.6 Certificates of Deposit 545.9 — — — 39.2 585.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 4,047.9 1,166.5 30.0 1.1 — 5,245.5 Other Asset-Backed 214.2 — — — — 214.2 Commercial Mortgage-Backed 37.6 — — — — 37.6 Other 54.8 — — — 521.5 576.3 Total $ 18,234.4 $ 4,257.7 $ 2,834.7 $ 334.0 $ 560.9 $ 26,221.7 Percent of Total 70 % 16 % 11 % 1 % 2 % 100 % Credit quality indicators are metrics that provide information regarding the relative credit risk of debt securities. Northern Trust maintains a high quality debt securities portfolio, with 96% and 97% of the HTM portfolio at March 31, 2024 and December 31, 2023, respectively, comprised of securities rated A or higher. The remaining HTM debt securities portfolio was comprised of 1% rated BBB at both March 31, 2024 and December 31, 2023 and 3% and 2% which were not rated by Moody’s, S&P Global, or Fitch Ratings at March 31, 2024 and December 31, 2023, respectively. Securities not explicitly rated were grouped where possible under the credit rating of the issuer of the security. Investment Security Gains and Losses. Proceeds of $2.0 billion from the sale of debt securities resulted in an investment security loss of $189.4 million for the three months ended March 31, 2024. The loss was comprised of $56.6 million in other asset-backed securities, $48.2 million in sub-sovereign, supranational and non-U.S. agency bonds, $34.8 million in U.S. government securities, $23.0 million in government-sponsored agency securities, $22.6 million in commercial mortgage-backed securities, and $4.2 million in covered bonds. Proceeds of $2.1 billion from the sale of debt securities resulted in investment security gains of $6.9 million for the three months ended March 31, 2023. The gain was comprised of a $9.8 million gain in obligations of states and political subdivisions, offset by losses of $1.2 million in corporate debt, $0.9 million in commercial mortgage-backed, and $0.8 million in other asset-backed securities.

Loans

Loans	3 Months Ended
	Mar. 31, 2024
Receivables [Abstract]
Loans	Loans Amounts outstanding for Loans, by segment and class, are shown in the following table. TABLE 41: LOANS (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Commercial Commercial and Institutional (1) $ 10,980.6 $ 11,555.3 Commercial Real Estate 5,333.0 5,134.2 Non-U.S. (1) 2,372.7 2,778.5 Other 6,730.8 5,944.8 Total Commercial 25,417.1 25,412.8 Personal Private Client 14,092.2 14,360.0 Residential Real Estate 6,315.2 6,327.1 Non-U.S. 387.2 428.8 Other 1,130.9 1,088.3 Total Personal 21,925.5 22,204.2 Total Loans $ 47,342.6 $ 47,617.0 (1) Commercial and institutional and commercial-non-U.S. combined include $5.1 billion and $4.5 billion of private equity capital call finance loans at March 31, 2024 and December 31, 2023, respectively. Residential real estate loans consist of traditional first lien mortgages and equity credit lines that generally require a loan-to-collateral value of no more than 65% to 80% at inception. Northern Trust’s equity credit line products generally have draw periods of up to 10 years and a balloon payment of any outstanding balance is due at maturity. Payments are interest-only with variable interest rates. Northern Trust does not offer equity credit lines that include an option to convert the outstanding balance to an amortizing payment loan. As of March 31, 2024 and December 31, 2023, equity credit lines totaled $229.9 million and $228.7 million, respectively, and equity credit lines for which first liens were held by Northern Trust represented 98% and 96% of the total equity credit lines as of March 31, 2024 and December 31, 2023, respectively. Included within the commercial-other, commercial-non-U.S., and personal-other classes are short-duration advances primarily related to the processing of custodied client investments, totaling $9.0 billion and $8.4 billion at March 31, 2024 and December 31, 2023, respectively. Demand deposit overdrafts reclassified as loan balances, primarily in personal-other, totaled $10.7 million and $12.1 million at March 31, 2024 and December 31, 2023, respectively. Loans classified as held for sale are recorded at the lower of cost or fair value. There were no loans classified as held for sale at March 31, 2024 or December 31, 2023. There were no loans sold for the three months ended March 31, 2024 and March 31, 2023. Credit Quality Indicators. Credit quality indicators are statistics, measurements or other metrics that provide information regarding the relative credit risk of loans. Northern Trust uses a variety of credit quality indicators to assess the credit risk of loans at the segment, class, and individual credit exposure levels. As part of its credit process, Northern Trust utilizes an internal borrower risk rating system to support identification, approval, and monitoring of credit risk. Borrower risk ratings are used in credit underwriting and management reporting. Risk ratings are used for ranking the credit risk of borrowers and their probability of their default. Each borrower is rated using one of a number of ratings models, which consider both quantitative and qualitative factors. The ratings models vary among classes of loans in order to capture the unique risk characteristics inherent within each particular type of credit exposure. Provided below are the more significant performance indicator attributes considered within Northern Trust’s borrower rating models, by loan class. • Commercial and Institutional: leverage, profit margin, liquidity, asset size and capital levels; • Commercial Real Estate: debt service coverage, loan-to-value ratio, leasing status and guarantor support; • Commercial-Other: leverage, profit margin, liquidity, asset size and capital levels; • Non-U.S.: leverage, profit margin, liquidity, return on assets and capital levels; • Residential Real Estate: payment history, credit bureau scores and loan-to-value ratio; • Private Client: cash-flow-to-debt and net worth ratios, leverage and liquidity; and • Personal-Other: cash-flow-to-debt and net worth ratios. While the criteria vary by model, the objective is for the borrower ratings to be consistent in both the measurement and ranking of risk. Each model is calibrated to a master rating scale to support this consistency. Ratings for borrowers not in default range from “1” for the strongest credits to “7” for the weakest non-defaulted credits. Ratings of “8” or “9” are used for defaulted borrowers. Borrower risk ratings are monitored and are revised when events or circumstances indicate a change is required. Risk ratings are generally validated at least annually. Loan segment and class balances as of March 31, 2024 and December 31, 2023 are provided in the following table, segregated by borrower ratings into “1 to 3,” “4 to 5” and “6 to 9” (watch list and nonaccrual status) categories by year of origination at amortized cost basis. Loans that are held for investment are reported at the principal amount outstanding, net of unearned income. TABLE 42: CREDIT QUALITY INDICATOR AT AMORTIZED COST BASIS BY ORIGINATION YEAR March 31, 2024 TERM LOANS REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2024 2023 2022 2021 2020 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 40.2 $ 411.4 $ 458.1 $ 715.7 $ 69.9 $ 539.6 $ 4,735.9 $ 15.0 $ 6,985.8 4 to 5 Category 51.1 757.9 757.4 627.1 117.6 218.3 1,196.2 78.6 3,804.2 6 to 9 Category — 4.2 75.5 57.6 3.9 1.7 45.9 1.8 190.6 Total Commercial and Institutional 91.3 1,173.5 1,291.0 1,400.4 191.4 759.6 5,978.0 95.4 10,980.6 C&I Gross Charge-offs — (7.3) (1.3) — — — — — (8.6) Commercial Real Estate Risk Rating: 1 to 3 Category 9.3 346.9 411.7 277.7 25.7 78.6 67.0 — 1,216.9 4 to 5 Category 151.9 1,617.5 1,087.7 392.9 208.6 340.6 204.5 7.8 4,011.5 6 to 9 Category — 16.1 35.3 30.3 2.5 20.4 — — 104.6 Total Commercial Real Estate 161.2 1,980.5 1,534.7 700.9 236.8 439.6 271.5 7.8 5,333.0 Commercial Real Estate Gross Charge-offs — — (2.4) — — — — — (2.4) Non-U.S. Risk Rating: 1 to 3 Category 950.4 — — 43.0 44.7 22.3 933.5 — 1,993.9 4 to 5 Category 176.9 26.9 0.8 — — 100.7 58.2 — 363.5 6 to 9 Category 1.1 — 14.2 — — — — — 15.3 Total Non-U.S. 1,128.4 26.9 15.0 43.0 44.7 123.0 991.7 — 2,372.7 Other Risk Rating: 1 to 3 Category 3,865.8 — — — — — — — 3,865.8 4 to 5 Category 2,865.0 — — — — — — — 2,865.0 Total Other 6,730.8 — — — — — — — 6,730.8 Other Gross Charge-offs — — — — — — — — — Total Commercial 8,111.7 3,180.9 2,840.7 2,144.3 472.9 1,322.2 7,241.2 103.2 25,417.1 Commercial Gross Charge-offs — (7.3) (3.7) — — — — — (11.0) Personal Private Client Risk Rating: 1 to 3 Category 28.9 472.7 109.5 49.5 60.1 96.0 5,056.1 168.2 6,041.0 4 to 5 Category 21.8 324.3 449.6 519.5 96.3 190.3 5,970.2 451.9 8,023.9 6 to 9 Category — 16.2 0.2 — — — 10.9 — 27.3 Total Private Client 50.7 813.2 559.3 569.0 156.4 286.3 11,037.2 620.1 14,092.2 Residential Real Estate Risk Rating: 1 to 3 Category 42.8 272.2 409.4 430.1 367.5 863.2 230.9 — 2,616.1 4 to 5 Category 44.3 203.3 738.1 766.8 675.2 1,042.9 161.7 — 3,632.3 6 to 9 Category — — 7.3 0.1 0.4 45.6 13.4 — 66.8 Total Residential Real Estate 87.1 475.5 1,154.8 1,197.0 1,043.1 1,951.7 406.0 — 6,315.2 Residential Real Estate Gross Charge-offs — — — — — (0.1) — — (0.1) Non-U.S. Risk Rating: 1 to 3 Category 0.4 3.8 — 0.6 — 4.5 43.9 — 53.2 4 to 5 Category — 23.9 15.5 23.3 — 24.9 231.0 7.4 326.0 6 to 9 Category 8.0 — — — — — — — 8.0 Total Non-U.S. 8.4 27.7 15.5 23.9 — 29.4 274.9 7.4 387.2 Other Risk Rating: 1 to 3 Category 636.3 — — — — — — — 636.3 4 to 5 Category 494.6 — — — — — — — 494.6 Total Other 1,130.9 — — — — — — — 1,130.9 Total Personal 1,277.1 1,316.4 1,729.6 1,789.9 1,199.5 2,267.4 11,718.1 627.5 21,925.5 Personal Gross Charge-offs — — — — — (0.1) — — (0.1) Total Loans $ 9,388.8 $ 4,497.3 $ 4,570.3 $ 3,934.2 $ 1,672.4 $ 3,589.6 $ 18,959.3 $ 730.7 $ 47,342.6 Total Loans Gross Charge-offs (1) $ — $ (7.3) $ (3.7) $ — $ — $ (0.1) $ — $ — $ (11.1) (1) There was $4 million of charge-offs for the three months ended March 31, 2023. December 31, 2023 TERM LOANS REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2023 2022 2021 2020 2019 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 443.9 $ 534.1 $ 668.3 $ 78.1 $ 137.2 $ 409.9 $ 4,909.8 $ 15.0 $ 7,196.3 4 to 5 Category 801.4 790.9 729.5 138.7 120.5 178.7 1,332.4 72.0 4,164.1 6 to 9 Category 13.8 70.0 60.8 12.0 0.1 1.7 34.7 1.8 194.9 Total Commercial and Institutional 1,259.1 1,395.0 1,458.6 228.8 257.8 590.3 6,276.9 88.8 11,555.3 Commercial Real Estate Risk Rating: 1 to 3 Category 403.6 389.9 159.1 23.9 37.8 44.8 51.0 — 1,110.1 4 to 5 Category 1,513.5 1,208.8 521.0 218.4 252.8 96.0 136.3 7.9 3,954.7 6 to 9 Category 16.1 — 30.5 — 8.2 14.6 — — 69.4 Total Commercial Real Estate 1,933.2 1,598.7 710.6 242.3 298.8 155.4 187.3 7.9 5,134.2 CRE Gross Charge-offs (0.7) (4.4) — — — — — — (5.1) Non-U.S. Risk Rating: 1 to 3 Category 487.9 — 43.2 65.2 34.2 3.3 760.0 — 1,393.8 4 to 5 Category 974.7 0.8 — — — 150.0 243.4 — 1,368.9 6 to 9 Category 1.5 14.3 — — — — — — 15.8 Total Non-U.S. 1,464.1 15.1 43.2 65.2 34.2 153.3 1,003.4 — 2,778.5 Other Risk Rating: 1 to 3 Category 4,313.2 — — — — — — — 4,313.2 4 to 5 Category 1,631.6 — — — — — — — 1,631.6 Total Other 5,944.8 — — — — — — — 5,944.8 Other Gross Charge-offs (0.6) — — — — — — — (0.6) Total Commercial 10,601.2 3,008.8 2,212.4 536.3 590.8 899.0 7,467.6 96.7 25,412.8 Commercial Gross Charge-offs (1.3) (4.4) — — — — — — (5.7) Personal Private Client Risk Rating: 1 to 3 Category 504.7 140.8 52.3 67.5 8.7 134.7 5,320.9 168.1 6,397.7 4 to 5 Category 290.1 488.2 655.1 100.9 158.8 44.7 5,721.5 447.8 7,907.1 6 to 9 Category 23.6 0.3 — — — 18.3 13.0 — 55.2 Total Private Client 818.4 629.3 707.4 168.4 167.5 197.7 11,055.4 615.9 14,360.0 Residential Real Estate Risk Rating: 1 to 3 Category 278.7 464.0 500.6 373.3 142.4 722.4 219.8 — 2,701.2 4 to 5 Category 191.6 694.9 717.4 686.7 290.0 805.3 170.3 — 3,556.2 6 to 9 Category — 10.9 — 0.7 1.6 43.6 12.9 — 69.7 Total Residential Real Estate 470.3 1,169.8 1,218.0 1,060.7 434.0 1,571.3 403.0 — 6,327.1 RRE Gross Charge-offs (0.8) — — — — (1.0) — — (1.8) Non-U.S. Risk Rating: 1 to 3 Category 15.5 — 0.6 — — 4.6 71.4 — 92.1 4 to 5 Category 12.7 16.0 39.2 — 16.4 8.9 236.1 7.4 336.7 6 to 9 Category — — — — — — — — — Total Non-U.S. 28.2 16.0 39.8 — 16.4 13.5 307.5 7.4 428.8 Other Risk Rating: 1 to 3 Category 461.7 — — — — — — — 461.7 4 to 5 Category 626.6 — — — — — — — 626.6 Total Other 1,088.3 — — — — — — — 1,088.3 Total Personal 2,405.2 1,815.1 1,965.2 1,229.1 617.9 1,782.5 11,765.9 623.3 22,204.2 Personal Gross Charge-Offs $ (0.8) $ — $ — $ — $ — $ (1.0) $ — $ — $ (1.8) Total Loans 13,006.4 4,823.9 4,177.6 1,765.4 1,208.7 2,681.5 19,233.5 720.0 47,617.0 Total Loans Gross Charge-Offs $ (2.1) $ (4.4) $ — $ — $ — $ (1.0) $ — $ — $ (7.5) Past Due Status. Past due status is based on the length of time from the contractual due date a principal or interest payment has been past due. For disclosure purposes, loans that are 29 days past due or less are reported as current. The following table provides balances and delinquency status of accrual and nonaccrual loans by segment and class, as well as the other real estate owned and nonaccrual asset balances, as of March 31, 2024 and December 31, 2023. TABLE 43: DELINQUENCY STATUS ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS March 31, 2024 Commercial Commercial and Institutional $ 10,963.0 $ 7.3 $ — $ 2.7 $ 10,973.0 $ 7.6 $ 10,980.6 $ 7.6 Commercial Real Estate 5,265.2 56.0 — 6.1 5,327.3 5.7 5,333.0 5.7 Non-U.S. 2,372.7 — — — 2,372.7 — 2,372.7 — Other 6,730.8 — — — 6,730.8 — 6,730.8 — Total Commercial 25,331.7 63.3 — 8.8 25,403.8 13.3 25,417.1 13.3 Personal Private Client 13,941.1 112.6 18.5 18.0 14,090.2 2.0 14,092.2 — Residential Real Estate 6,261.2 18.5 10.8 3.0 6,293.5 21.7 6,315.2 21.7 Non-U.S. 354.8 32.4 — — 387.2 — 387.2 — Other 1,130.9 — — — 1,130.9 — 1,130.9 — Total Personal 21,688.0 163.5 29.3 21.0 21,901.8 23.7 21,925.5 21.7 Total Loans $ 47,019.7 $ 226.8 $ 29.3 $ 29.8 $ 47,305.6 $ 37.0 $ 47,342.6 $ 35.0 Other Real Estate Owned $ — Total Nonaccrual Assets $ 37.0 ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS December 31, 2023 Commercial Commercial and Institutional $ 11,374.6 $ 163.7 $ 0.7 $ — $ 11,539.0 $ 16.3 $ 11,555.3 $ 4.1 Commercial Real Estate 5,123.7 4.4 6.1 — 5,134.2 — 5,134.2 — Non-U.S. 2,778.5 — — — 2,778.5 — 2,778.5 — Other 5,944.8 — — — 5,944.8 — 5,944.8 — Total Commercial 25,221.6 168.1 6.8 — 25,396.5 16.3 25,412.8 4.1 Personal Private Client 14,240.0 63.9 24.8 11.0 14,339.7 20.3 14,360.0 18.3 Residential Real Estate 6,283.0 7.5 0.5 9.1 6,300.1 27.0 6,327.1 27.0 Non-U.S 428.2 — 0.6 — 428.8 — 428.8 — Other 1,088.3 — — — 1,088.3 — 1,088.3 — Total Personal 22,039.5 71.4 25.9 20.1 22,156.9 47.3 22,204.2 45.3 Total Loans $ 47,261.1 $ 239.5 $ 32.7 $ 20.1 $ 47,553.4 $ 63.6 $ 47,617.0 $ 49.4 Other Real Estate Owned $ 1.5 Total Nonaccrual Assets $ 65.1 Interest income that would have been recorded for nonaccrual loans in accordance with their original terms was $0.7 million for the three months ended March 31, 2024 and 2023. Northern Trust may obtain physical possession of real estate via foreclosure on an in-substance repossession. As of March 31, 2024 and December 31, 2023, Northern Trust held foreclosed real estate properties with an immaterial carrying value as a result of obtaining physical possession. In addition, as of March 31, 2024 and December 31, 2023, Northern Trust had loans with a carrying value of $3.7 million and $3.5 million, respectively, for which formal foreclosure proceedings were in process. Loan Modifications to Borrowers Experiencing Financial Difficulty For borrowers experiencing financial difficulties, Northern Trust may provide payment relief by modifying the terms of the original loan. Loan modifications to borrowers experiencing financial difficulty involve primarily extensions of term, deferrals of principal and interest, interest rate concessions, and other modifications or a combination thereof. Northern Trust considers payment deferrals of less than 90 days as insignificant, absent any material modifications to other loan terms. The following table shows the amortized cost basis of loan modifications provided to financially distressed borrowers that impacted the respective cash flows of the underlying loans as of March 31, 2024 and March 31, 2023, disaggregated by relevant class of financing receivable and type of modification provided. TABLE 44: LOAN MODIFICATIONS MADE TO BORROWERS EXPERIENCING FINANCIAL DIFFICULTY THREE MONTHS ENDED MARCH 31, 2024 THREE MONTHS ENDED MARCH 31, 2023 ($ In Millions) LOAN MODIFICATION DETAIL AMORTIZED COST BASIS % OF TOTAL SEGMENT AMORTIZED COST BASIS % OF TOTAL SEGMENT Commercial Total Commercial $ — — % $ — — % Personal Residential Real Estate Deferred Principal and Interest $ — — % $ 2.9 0.05 % Residential Real Estate Extension of Term 0.1 — — — Private Client Extension of Term 0.2 — — — Total Personal $ 0.3 — % $ 2.9 0.05 % Total Loans $ 0.3 — % $ 2.9 0.05 % The following table describes the financial effect of the modifications made to borrowers experiencing financial difficulty. TABLE 45: FINANCIAL EFFECT OF MODIFICATIONS MADE TO BORROWERS EXPERIENCING FINANCIAL DIFFICULTY THREE MONTHS ENDED MARCH 31, 2024 THREE MONTHS ENDED MARCH 31, 2023 FINANCIAL EFFECT FINANCIAL EFFECT PRINCIPAL AND INTEREST DEFERRAL Personal Residential Real Estate — Northern Trust provided a weighted average of 180 days payment deferrals to borrowers for immaterial principal and interest deferral amounts. These payments are, in general, due at the end of the deferral period. TERM EXTENSION Personal Residential Real Estate Northern Trust provided weighted average term extensions of 14 months. — Private Client Northern Trust provided weighted average term extensions of 22 months. — The effectiveness of Northern Trust’s modification efforts is measured by the loans’ respective past due status under the modified terms as of the end of the period. Of the loans that were modified in the last 12 months, and were not performing in accordance with their modified terms and considered past due for purposes of these disclosures as of March 31, 2024, there were $0.5 million 30-89 days past due and $7.8 million 90 days and greater past due. Given that principal and interest were deferred under the modified terms for all financially distressed modifications processed in the first quarter of 2023, none of the modified loans were considered past-due as of March 31, 2023. As of three months ended March 31, 2024, Northern Trust charged-off $8.2 million related to modifications to borrowers experiencing financial difficulty that had been modified in the last 12 months. There were no defaults and related charge-offs since the adoption of the ASU 2022-02 as of January 1, 2023 through the three months ended March 31, 2023. There were no undrawn loan commitments or standby letters of credit issued to financially distressed borrowers for which Northern Trust has modified the payment terms of the loans as of March 31, 2024 and December 31, 2023, respectively. The expected credit loss for nonaccrual loans including loan modifications to borrowers experiencing financial difficulty is measured based on either the expected future cash flows, the value of collateral, or other factors that may impact the borrower’s ability to pay. If the discounted cash flow method is utilized, the credit loss is measured based upon the present value of expected future cash flows, discounted at the effective interest rate based on the post-modification contractual rate. If a loan’s contractual interest rate varies based on subsequent changes in an independent factor, such as an index or rate, the loan’s effective interest rate is calculated based on the factor as it changes over the life of the loan. Northern Trust elected not to project changes in the factor for purposes of estimating expected future cash flows. Further, Northern Trust elected not to adjust the effective interest rate for prepayments. If the loan is collateral dependent, the expected loss is measured based on the fair value of the collateral at the reporting date. If the loan valuation is less than the recorded value of the loan, either an allowance is established or a charge-off is recorded for the difference. The nature and extent of further deterioration in credit quality, including a subsequent default, is considered in the determination of an appropriate level of allowance for credit losses for all loan modifications to borrowers experiencing financial difficulty.

Allowance for Credit Losses

Allowance for Credit Losses	3 Months Ended
	Mar. 31, 2024
Receivables [Abstract]
Allowance for Credit Losses	Allowance for Credit Losses Allowance and Provision for Credit Losses. The allowance for credit losses—which represents management’s best estimate of lifetime expected credit losses related to various portfolios subject to credit risk, off-balance-sheet credit exposures, and specific borrower relationships—is determined by management through a disciplined credit review process. Northern Trust measures expected credit losses of financial assets with similar risk characteristics on a collective basis. A financial asset is measured individually if it does not share similar risk characteristics with other financial assets and the related allowance is determined through an individual evaluation. Management’s estimates utilized in establishing an appropriate level of allowance for credit losses are not dependent on any single assumption. In determining an appropriate allowance level, management evaluates numerous variables and takes into consideration past events, current conditions, and reasonable and supportable forecasts. The results of the credit reserve estimation methodology are reviewed quarterly by Northern Trust’s Credit Loss Reserve Committee, which receives input from Financial Risk Management, Treasury, Corporate Finance, the Economic Research Department, and each of Northern Trust’s reporting business units. The Credit Loss Reserve Committee determines the probability weights applied to each forecast approved by Northern Trust’s Macroeconomic Scenario Development Committee, and also reviews and approves qualitative adjustments to the collective allowance in line with Northern Trust’s qualitative adjustment framework. The Provision for Credit Losses on the consolidated statements of income represents the change in the Allowance for Credit Losses on the consolidated balance sheets after accounting for net charge-offs or recoveries and is the charge to current period earnings. It represents the amount needed to maintain the Allowance for Credit Losses on the consolidated balance sheets at an appropriate level to absorb lifetime expected credit losses related to financial assets in scope. Actual losses may vary from current estimates and the amount of the Provision for Credit Losses may be either greater or less than actual net charge-offs. The following table provides information regarding changes in the total allowance for credit losses during the three months ended March 31, 2024 and 2023. TABLE 46: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES THREE MONTHS ENDED MARCH 31, 2024 (In Millions) LOANS UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT HELD TO MATURITY DEBT SECURITIES OTHER FINANCIAL ASSETS TOTAL Balance at Beginning of Period $ 178.7 $ 26.9 $ 12.7 $ 0.9 $ 219.2 Charge-Offs (11.1) — — — (11.1) Recoveries 0.7 — — — 0.7 Net Recoveries (Charge-Offs) (10.4) — — — (10.4) Provision for Credit Losses (1) (5.9) (1.7) (0.3) 0.1 (7.8) Balance at End of Period $ 162.4 $ 25.2 $ 12.4 $ 1.0 $ 201.0 (1) The table excludes a negative provision for credit losses of $0.7 million for the three months ended March 31, 2024 for AFS debt securities. See further detail in Note 4—Securities. THREE MONTHS ENDED MARCH 31, 2023 (In Millions) LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT HELD TO MATURITY DEBT SECURITIES OTHER FINANCIAL ASSETS TOTAL Balance at Beginning of Period $ 144.3 $ 38.5 $ 16.0 $ 0.8 $ 199.6 Charge-Offs (4.0) — — — (4.0) Recoveries 1.1 — — — 1.1 Net Recoveries (Charge-Offs) (2.9) — — — (2.9) Provision for Credit Losses (1) 18.5 (4.2) — 0.2 14.5 Balance at End of Period $ 159.9 $ 34.3 $ 16.0 $ 1.0 $ 211.2 (1) The table excludes a provision for credit losses of $0.5 million for the three months ended March 31, 2023 for AFS debt securities. See further detail in Note 4—Securities. Excluding the impact of the negative provision for available for sale debt securities, there was a negative Provision for Credit Losses of $7.8 million in the current quarter, as compared to a $14.5 million provision in the prior-year quarter. The negative provision resulted from decreases in both individual and collective reserves. The decrease in individual reserves was driven by one Commercial and Institutional (C&I) loan that was charged-off in the current quarter. The decrease in collective reserve was primarily in the C&I portfolio, driven by improvement in the quality of the portfolio, and in the Commercial Real Estate (CRE) portfolio, driven by improved macroeconomic factors. The reserve evaluated on a collective basis relates to pooled financial assets sharing similar risk characteristics. There were net charge-offs of $10.4 million during the three months ended March 31, 2024, as compared to net charge-offs of $2.9 million for the three months ended March 31, 2023. For further detail, please see the Allowance for the Loan Portfolio and the Allowance for Held to Maturity Debt Securities Portfolio sections below. The portion of the allowance assigned to loans, HTM debt securities, and other financial assets is presented as a contra asset in Allowance for Credit Losses on the consolidated balance sheets. The portion of the allowance assigned to undrawn loan commitments and standby letters of credit is reported in Other Liabilities on the consolidated balance sheets. For credit exposure and the associated allowance related to fee receivables, please refer to Note 13—Revenue from Contracts with Clients. For information related to the allowance for AFS debt securities, please refer to Note 4—Securities. For all other financial assets recognized at amortized cost, which include Cash and Due from Banks, Other Central Bank Deposits, Interest Bearing Deposits with Banks, and Other Assets, please refer to the Allowance for Other Financial Assets section within this footnote. Forecasting and Reversion. Estimating expected lifetime credit losses requires the consideration of the effect of future economic conditions. Northern Trust employs multiple scenarios over a reasonable and supportable period (currently two years) to project future conditions. Key variables determined to be relevant for projecting credit losses on the portfolios in scope include macroeconomic factors, such as corporate profits, unemployment, disposable income, and real estate price indices, as well as financial market factors such as market volatility and credit spreads. For periods beyond the reasonable and supportable period, Northern Trust reverts to its own historical loss experiences on a straight-line basis over four quarters. The primary forecast in the current quarter reflects an outlook of steady growth, with inflation and labor markets stabilizing and interest rates falling. Recognizing the uncertainty in the primary forecast, an alternative scenario is also considered, which reflects a recession that incorporates the experiences of a wider set of historical economic cycles. Contractual Term. Northern Trust estimates expected credit losses over the contractual term of the financial assets adjusted for prepayments, unless prepayments are not relevant to specific portfolios or sub-portfolios. Extension and renewal options are typically not considered since it is not Northern Trust’s practice to enter into arrangements where the borrower has the unconditional option to renew, or a conditional extension option whereby the conditions are beyond Northern Trust’s control. Allowance for the Loan Portfolio. The following table provides information regarding changes in the total allowance for credit losses related to loans, including undrawn loan commitments and standby letters of credit, by segment during the three months ended March 31, 2024 and 2023. TABLE 47: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO LOANS THREE MONTHS ENDED MARCH 31, 2024 LOANS UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 146.8 $ 31.9 $ 178.7 $ 24.9 $ 2.0 $ 26.9 Charge-Offs (11.0) (0.1) (11.1) — — — Recoveries — 0.7 0.7 — — — Net Recoveries (Charge-Offs) (11.0) 0.6 (10.4) — — — Provision for Credit Losses (4.1) (1.8) (5.9) (2.4) 0.7 (1.7) Balance at End of Period $ 131.7 $ 30.7 $ 162.4 $ 22.5 $ 2.7 $ 25.2 THREE MONTHS ENDED MARCH 31, 2023 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 116.2 $ 28.1 $ 144.3 $ 36.3 $ 2.2 $ 38.5 Charge-Offs (4.0) — (4.0) — — — Recoveries — 1.1 1.1 — — — Net Recoveries (Charge-Offs) (4.0) 1.1 (2.9) — — — Provision for Credit Losses 18.6 (0.1) 18.5 (5.0) 0.8 (4.2) Balance at End of Period $ 130.8 $ 29.1 $ 159.9 $ 31.3 $ 3.0 $ 34.3 Allowance Related to Credit Exposure Evaluated on a Collective Basis. Expected credit losses are measured on a collective basis as long as the financial assets included in the respective pool share similar risk characteristics. If financial assets are deemed to not share similar risk characteristics, an individual assessment is warranted. The allowance estimation methodology for the collective assessment is based on data representative of the Corporation’s financial asset portfolio from a historical observation period that includes both expansionary and recessionary periods. The estimation methodology and the related qualitative adjustment framework segregate the loan portfolio into homogeneous segments based on similar risk characteristics or risk monitoring methods. Northern Trust utilizes a quantitative probability of default/loss given default approach for the calculation of its credit allowance on a collective basis. For each of the different parameters, specific credit models or qualitative estimation methodologies for the individual loan segments were developed. For each segment, the probability of default and the loss given default are applied to the exposure at default for each projected quarter to determine the quantitative component of the allowance. The quantitative allowance is then reviewed within the qualitative adjustment framework, through which management applies judgment by assessing internal risk factors, potential limitations in the quantitative methodology, and environmental factors that are not fully contemplated in the forecast to compute an adjustment to the quantitative allowance for each segment and class of the loan portfolio. Allowance Related to Credit Exposure Evaluated on an Individual Basis. The individual allowance is determined through individual evaluation of loans and lending-related commitments that have defaulted, generally those with borrower ratings of 8 and 9, that are based on expected future cash flows, the value of collateral, and other factors that may impact the borrower’s ability to pay. For defaulted loans for which the amount of allowance, if any, is determined based on the value of the underlying real estate collateral, third-party appraisals are typically obtained and utilized by management. These appraisals are generally less than twelve months old and are subject to adjustments to reflect management’s judgment as to the realizable value of the collateral. The following table provides information regarding the recorded investments in loans and the allowance for credit losses for loans and undrawn loan commitments and standby letters of credit by segment as of March 31, 2024 and December 31, 2023. TABLE 48: RECORDED INVESTMENTS IN LOANS MARCH 31, 2024 DECEMBER 31, 2023 (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Loans Evaluated on an Individual Basis $ 14.5 $ 38.7 $ 53.2 $ 33.7 $ 62.6 $ 96.3 Evaluated on a Collective Basis 25,402.6 21,886.8 47,289.4 25,379.1 22,141.6 47,520.7 Total Loans 25,417.1 21,925.5 47,342.6 25,412.8 22,204.2 47,617.0 Allowance for Credit Losses on Loans Evaluated on an Individual Basis 0.5 2.0 2.5 11.4 2.0 13.4 Evaluated on a Collective Basis 131.2 28.7 159.9 135.4 29.9 165.3 Allowance Assigned to Loans 131.7 30.7 162.4 146.8 31.9 178.7 Allowance for Undrawn Loan Commitments and Standby Letters of Credit Evaluated on a Collective Basis 22.5 2.7 25.2 24.9 2.0 26.9 Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit 22.5 2.7 25.2 24.9 2.0 26.9 Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit $ 154.2 $ 33.4 $ 187.6 $ 171.7 $ 33.9 $ 205.6 Northern Trust analyzes its exposure to credit losses from both on-balance-sheet and off-balance-sheet activity using a consistent methodology for the quantitative framework as well as the qualitative framework. For purposes of estimating the allowance for credit losses for undrawn loan commitments and standby letters of credit, the exposure at default includes an estimated drawdown of unused credit based on credit utilization factors, resulting in a proportionate amount of expected credit losses. Allowance for Held to Maturity Debt Securities Portfolio. The following table provides information regarding changes in the total allowance for credit losses for HTM debt securities during the three months ended March 31, 2024 and 2023. TABLE 49: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO HELD TO MATURITY DEBT SECURITIES THREE MONTHS ENDED MARCH 31, 2024 (In Millions) CORPORATE DEBT NON-U.S. GOVERNMENT SUB-SOVEREIGN, SUPRANATIONAL, AND NON-U.S. AGENCY BONDS OBLIGATIONS OF STATES AND POLITICAL SUBDIVISIONS (1) COVERED BONDS OTHER TOTAL Balance at Beginning of Period $ 0.9 $ 3.5 $ 2.2 $ 1.2 $ 0.1 $ 4.8 $ 12.7 Provision for Credit Losses (0.1) — (0.1) (0.1) — — (0.3) Balance at End of Period $ 0.8 $ 3.5 $ 2.1 $ 1.1 $ 0.1 $ 4.8 $ 12.4 (1) The allowance for Obligations of States and Political Subdivisions is related to (non pre-refunded) municipal securities that do not fall under Northern Trust’s zero-loss assumption. THREE MONTHS ENDED MARCH 31, 2023 (In Millions) CORPORATE DEBT NON-U.S. GOVERNMENT SUB-SOVEREIGN, SUPRANATIONAL, AND NON-U.S. AGENCY BONDS OBLIGATIONS OF STATES AND POLITICAL SUBDIVISIONS COVERED BONDS OTHER TOTAL Balance at Beginning of Period $ 1.9 $ 3.6 $ 4.0 $ 1.5 $ 0.1 $ 4.9 $ 16.0 Provision for Credit Losses — 0.3 0.1 (0.2) — (0.2) — Balance at End of Period $ 1.9 $ 3.9 $ 4.1 $ 1.3 $ 0.1 $ 4.7 $ 16.0 HTM debt securities classified as U.S. government, government sponsored agency, and certain securities classified as obligations of states and political subdivisions are considered to be guarantees of the U.S. government or an agency of the U.S. government and, therefore, an allowance for credit losses is not estimated for such investments as the expected probability of non-payment of the amortized cost basis is zero. HTM debt securities classified as “other asset-backed securities” represent pools of underlying receivables from which the cash flows are used to pay the bonds that vary in seniority. Utilizing a qualitative estimation approach, the allowance for other asset-backed securities is assessed by evaluating underlying pool performance based on delinquency rates and available credit support. HTM debt securities classified as “other” relate to investments purchased by Northern Trust to fulfill its obligations under the Community Reinvestment Act (CRA). Northern Trust fulfills its obligations under the CRA by making qualified investments for purposes of supporting institutions and programs that benefit low-to-moderate income communities within Northern Trust’s market area. The allowance for CRA investments is assessed using a qualitative estimation approach primarily based on internal historical performance experience and default history of the underlying CRA portfolios to determine a quantitative component of the allowance. The allowance estimation methodology for all other HTM debt securities is developed using a combination of external and internal data. The estimation methodology groups securities with shared characteristics for which the probability of default and the loss given default are applied to the total exposure at default to determine a quantitative component of the allowance. Allowance for Other Financial Assets. The allowance for Other Financial Assets consists of the allowance for Due from Banks, Other Central Bank Deposits, Interest Bearing Deposits with Banks, and Other Assets. The Other Assets category includes other miscellaneous credit exposures reported in Other Assets on the consolidated balance sheets. The allowance estimation methodology for Other Financial Assets primarily utilizes a similar approach as the one used for the HTM debt securities portfolio. It consists of a combination of externally and internally developed loss data, adjusted for the appropriate contractual term. Northern Trust’s portfolio of Other Financial Assets is composed mostly of institutions within the “1 to 3” internal borrower rating category and is expected to exhibit minimal to modest likelihood of loss. The Allowance for Credit Losses related to Other Financial Assets was $1.0 million and $0.9 million as of March 31, 2024 and December 31, 2023, respectively. Accrued Interest. Accrued interest balances are reported within Other Assets on the consolidated balance sheets. Northern Trust elected not to measure an allowance for credit losses for accrued interest receivables related to its loan and securities portfolio as its policy is to write-off uncollectible accrued interest receivable balances in a timely manner. Accrued interest is written off by reversing interest income during the period the financial asset is moved from an accrual to a nonaccrual status. The following table provides the amount of accrued interest excluded from the amortized cost basis of the following portfolios. TABLE 50: ACCRUED INTEREST (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Loans $ 253.0 $ 241.7 Debt Securities Held to Maturity 69.8 72.0 Available for Sale 175.0 129.2 Other Financial Assets 110.3 86.0 Total $ 608.1 $ 528.9 The amount of accrued interest reversed through interest income for loans was immaterial for the three months ended March 31, 2024 and 2023, and there was no accrued interest reversed through interest income related to any other financial assets for the three months ended March 31, 2024 and 2023.

Pledged Assets, Collateral and

Pledged Assets, Collateral and Restricted Assets	3 Months Ended
	Mar. 31, 2024
Transfers and Servicing [Abstract]
Pledged Assets, Collateral and Restricted Assets	Pledged Assets, Accepted Collateral and Restricted Assets Pledged Assets . For our liquidity management strategy, we may pledge loans and/or securities to various financial market utilities to allow for client payment, clearing and settlement processing as part of our custody services. We may pledge loans or securities to Central Banks, Federal Home Loan Bank (FHLB) of Chicago and third parties for various purposes, for example: securing public and trust deposits, repurchase agreements, borrowings and derivative contracts. As of March 31, 2024 and December 31, 2023, respectively, $1.4 billion and $1.1 billion of collateral we pledge, related to loans and/or securities, is eligible to be repledged or sold by the secured party. The following table presents the carrying value of Northern Trust's pledged assets by type. TABLE 51: TYPE OF PLEDGED ASSETS (In Billions) MARCH 31, 2024 DECEMBER 31, 2023 Debt Securities (1) $ 30.8 $ 33.0 Loans (2) 10.6 10.3 Total Pledged Assets $ 41.4 $ 43.3 (1) Debt securities are comprised of held to maturity and available for sale securities. (2) Loans pledged at the FHLB of Chicago and the Federal Reserve Bank of Chicago. Accepted Collateral. Northern Trust accepts financial assets as collateral that it may, in some instances, be permitted to repledge or sell. The collateral is generally obtained under certain reverse repurchase agreements and derivative contracts. The following table presents the fair value of securities accepted as collateral. TABLE 52: ACCEPTED COLLATERAL (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Collateral that may be repledged or sold Reverse repurchase agreements (1)(2) $ 66,327.9 $ 62,767.8 Derivative contracts 3.6 12.2 Collateral that may not be repledged or sold Reverse repurchase agreements — — Total Collateral Accepted $ 66,331.5 $ 62,780.0 (1) The fair value of securities collateral that was repledged or sold totaled $65.7 billion and $62.0 billion at March 31, 2024 and December 31, 2023, respectively. (2) This includes collateral accepted as related to the sponsored member program. Refer to Note 20—Commitments and Contingent Liabilities for further information. Restricted Assets . Certain cash may be restricted in terms of usage or withdrawal. As a result of the continuing military conflict involving Ukraine and the Russian Federation and related sanctions and legal restrictions in place, cash balances denominated in Russian rubles received for the benefit of certain clients in our Asset Servicing business are subject to distribution restrictions. As of March 31, 2024 and December 31, 2023, these balances totaled $818.9 million and $722.2 million, respectively, and are reported in Cash and Due from Banks on the consolidated balance sheets. At March 31, 2024 and December 31, 2023, Northern Trust held cash of $563.4 million and $575.2 million, respectively, to meet non-U.S. reserve requirements. As a result of the economic environment arising from the COVID-19 pandemic, the Federal Reserve reduced the U.S. reserve requirement to zero percent on March 26, 2020. There were no average deposits required to meet Federal Reserve Bank reserve requirements for the three months ended March 31, 2024 and 2023, respectively.

Goodwill and Other Intangibles

Goodwill and Other Intangibles	3 Months Ended
	Mar. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangibles	Goodwill and Other Intangibles Goodwill. Changes by reporting segment in the carrying amount of Goodwill for the three months ended March 31, 2024, including the effect of foreign exchange rates on non-U.S. dollar denominated balances, were as follows. TABLE 53: GOODWILL (In Millions) ASSET WEALTH MANAGEMENT TOTAL Balance at December 31, 2023 $ 621.9 $ 80.4 $ 702.3 Foreign Exchange Rates (4.8) — (4.8) Balance at March 31, 2024 $ 617.1 $ 80.4 $ 697.5 Other Intangible Assets Subject to Amortization . The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of March 31, 2024 and December 31, 2023 were as follows. TABLE 54: OTHER INTANGIBLE ASSETS (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Gross Carrying Amount $ 130.9 $ 135.0 Less: Accumulated Amortization 63.9 63.4 Net Book Value $ 67.0 $ 71.6 Other intangible assets consist primarily of the value of acquired client relationships and are included within Other Assets on the consolidated balance sheets. Amortization expense related to other intangible assets totaled $2.3 million for the three months ended March 31, 2024 and March 31, 2023. Amortization for the remainder of 2024 and for the years 2025, 2026, 2027, and 2028 is estimated to be $6.9 million, $8.6 million, $8.3 million, $8.0 million, and $7.4 million, respectively. Capitalized Software. The gross carrying amount and accumulated amortization of capitalized software as of March 31, 2024 and December 31, 2023 were as follows. TABLE 55: CAPITALIZED SOFTWARE (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Gross Carrying Amount $ 3,905.3 $ 3,781.7 Less: Accumulated Amortization 1,893.9 1,754.2 Net Book Value $ 2,011.4 $ 2,027.5 Capitalized software, which is included in Other Assets on the consolidated balance sheets, consists primarily of purchased software, software licenses, and allowable internal costs, including compensation relating to software developed for internal use. Fees paid for the use of software licenses that are not hosted by Northern Trust are expensed as incurred. Amortization expense, which is included in Equipment and Software on the consolidated statements of income, totaled $140.4 million and $121.3 million for the three months ended March 31, 2024 and March 31, 2023, respectively.

Reporting Segments

Reporting Segments	3 Months Ended
	Mar. 31, 2024
Segment Reporting [Abstract]
Reporting Segments	Reporting Segments Northern Trust is organized around its two client-focused reporting segments: Asset Servicing and Wealth Management. Asset management and related services are provided to Asset Servicing and Wealth Management clients primarily by the Asset Management business. The revenue and expenses of Asset Management and certain other support functions are allocated fully to Asset Servicing and Wealth Management. Reporting segment financial information, presented on an internal management-reporting basis, is determined by accounting systems used to allocate revenue and expense to each segment, and incorporates processes for allocating assets, liabilities, equity and the applicable interest income and expense utilizing a funds transfer pricing (FTP) methodology. Under the methodology, assets and liabilities receive a funding charge or credit that considers interest rate risk, liquidity risk, and other product characteristics on an instrument level. Additionally, segment information is presented on an FTE basis as management believes an FTE presentation provides a clearer indication of net interest income. The adjustment to an FTE basis has no impact on Net Income. Revenues, expenses and average assets are allocated to Asset Servicing and Wealth Management, with the exception of non-recurring activities such as certain corporate transactions and costs incurred associated with acquisitions, divestitures, litigation, restructuring, and tax adjustments not directly attributable to a specific reporting segment, which are reported within the Other segment. Effective January 2024, Northern Trust implemented certain enhancements to its FTP methodology, impacting the allocation of Net Interest Income to the Asset Servicing and Wealth Management segments. As a result, the approximate impact on the Asset Servicing and Wealth Management segments was a $31 million decrease and a $31 million increase in Net Interest Income, respectively, for the three months ended March 31, 2024. Prior-period segment results have not been revised to reflect this methodology change. Reporting segment results are subject to reclassification when organizational changes are made. The results are also subject to refinements in revenue and expense allocation methodologies, which are typically reflected on a prospective basis. The following table presents the earnings contributions and average assets of Northern Trust’s reporting segments for the three-month periods ended March 31, 2024 and 2023. TABLE 56: RESULTS OF REPORTING SEGMENTS ($ In Millions) ASSET SERVICING WEALTH MANAGEMENT OTHER RECONCILING ITEMS TOTAL CONSOLIDATED THREE MONTHS ENDED MARCH 31, 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Noninterest Income Trust, Investment and Other Servicing Fees $ 639.6 $ 603.0 $ 503.3 $ 460.6 $ — $ — $ — $ — $ 1,142.9 $ 1,063.6 Foreign Exchange Trading Income (Loss) 59.9 54.9 (2.9) (1.9) — — — — 57.0 53.0 Other Noninterest Income (Loss) 70.8 63.2 38.5 34.3 (190.5) (0.7) — — (81.2) 96.8 Total Noninterest Income (Loss) 770.3 721.1 538.9 493.0 (190.5) (0.7) — — 1,118.7 1,213.4 Net Interest Income 293.8 312.1 241.6 232.3 — — (7.3) (13.2) 528.1 531.2 Revenue 1,064.1 1,033.2 780.5 725.3 (190.5) (0.7) (7.3) (13.2) 1,646.8 1,744.6 Provision for Credit Losses (5.8) (2.9) (1.7) 17.9 (1.0) — — — (8.5) 15.0 Noninterest Expense 852.7 801.0 491.7 469.2 20.3 15.4 — — 1,364.7 1,285.6 Income before Income Taxes 217.2 235.1 290.5 238.2 (209.8) (16.1) (7.3) (13.2) 290.6 444.0 Provision for Income Taxes 56.6 60.5 81.4 66.1 (54.8) (4.0) (7.3) (13.2) 75.9 109.4 Net Income $ 160.6 $ 174.6 $ 209.1 $ 172.1 $ (155.0) $ (12.1) $ — $ — $ 214.7 $ 334.6 Percentage of Consolidated Net Income N/M 52 % N/M 52 % N/M (4) % N/A N/A 100 % 100 % Average Assets $ 106,955.0 $ 111,215.3 $ 38,163.3 $ 36,844.6 $ — $ — N/A N/A $ 145,118.3 $ 148,059.9 Note: Segment results are stated on an FTE basis. The FTE adjustments are eliminated in the reconciling items column with the Corporation’s total consolidated financial results stated on a GAAP basis. The adjustment to an FTE basis has no impact on Net Income.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock. The Corporation is authorized to issue 10 million shares of preferred stock without par value. The Board of Directors is authorized to fix the particular designations, preferences and relative, participating, optional and other special rights and qualifications, limitations or restrictions for each series of preferred stock issued. As of March 31, 2024, 5,000 shares of Series D Non-Cumulative Perpetual Preferred Stock (Series D Preferred Stock) and 16,000 shares of Series E Non-Cumulative Perpetual Preferred Stock (Series E Preferred Stock) were outstanding. Series D Preferred Stock. As of March 31, 2024, the Corporation had issued and outstanding 500,000 depositary shares, each representing a 1/100th ownership interest in a share of Series D Preferred Stock, issued in August 2016. Equity related to Series D Preferred Stock as of March 31, 2024 and December 31, 2023 was $493.5 million. Shares of the Series D Preferred Stock have no par value and a liquidation preference of $100,000 (equivalent to $1,000 per depositary share). Dividends on the Series D Preferred Stock, which are not mandatory, accrue and are payable on the liquidation preference amount, on a non-cumulative basis, at a rate per annum equal to (i) 4.60% from the original issue date of the Series D Preferred Stock to but excluding October 1, 2026; and (ii) a floating rate equal to the three-month CME Term Secured Overnight Finance Rate (SOFR), as administered by CME Group Benchmark Administration, Ltd., plus a statutory spread adjustment of 0.26161% (as set forth in the final rule to implement the LIBOR Act) plus 3.202% from and including October 1, 2026. Fixed rate dividends are payable in arrears on the first day of April and October of each year, through and including October 1, 2026, and floating rate dividends will be payable in arrears on the first day of January, April, July and October of each year, commencing on January 1, 2027. On January 17, 2024, the Corporation declared a cash dividend of $2,300.00 per share of Series D Preferred Stock payable on April 1, 2024, to stockholders of record as of March 15, 2024. Series E Preferred Stock. As of March 31, 2024, the Corporation had issued and outstanding 16 million depositary shares, each representing 1/1,000th ownership interest in a share of Series E Preferred Stock, issued in November 2019. Equity related to Series E Preferred Stock as of March 31, 2024 and December 31, 2023 was $391.4 million. Shares of the Series E Preferred Stock have no par value and a liquidation preference of $25,000 (equivalent to $25 per depositary share). Dividends on the Series E Preferred Stock, which are not mandatory, will accrue and be payable on the liquidation preference amount, on a non-cumulative basis, quarterly in arrears on the first day of January, April, July and October of each year, at a rate per annum equal to 4.70%. On January 17, 2024, the Corporation declared a cash dividend of $293.75 per share of Series E Preferred Stock payable on April 1, 2024, to stockholders of record as of March 15, 2024. Common Stock. The Corporation’s current stock repurchase authorization to repurchase up to 25 million shares was approved by the Board of Directors in October 2021. Shares are repurchased by the Corporation to, among other things, manage the Corporation’s capital levels. Repurchased shares are used for general purposes, including the issuance of shares under stock option and other incentive plans. The repurchase authorization approved by the Board of Directors has no expiration date. For the three months ended March 31, 2024, the Corporation repurchased 1,647,526 shares of common stock, at a total cost of $132.0 million ($80.11 average price per share), including 373,623 shares withheld to satisfy tax withholding obligations related to share-based compensation. For the three months ended March 31, 2023, the Corporation repurchased 1,050,227 shares of common stock, at a total cost of $100.9 million ($96.04 average prices per share), including 326,811 shares withheld to satisfy tax withholding obligations related to share-based compensation.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) The following tables summarize the components of Accumulated Other Comprehensive Income (Loss) (AOCI) at March 31, 2024 and 2023, and changes during the three months then ended. TABLE 57: SUMMARY OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED MARCH 31, 2024 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2023 $ (923.9) $ 0.8 $ 203.6 $ (418.4) $ (1,137.9) Net Change 213.4 (0.7) 4.6 3.0 220.3 Balance at March 31, 2024 $ (710.5) $ 0.1 $ 208.2 $ (415.4) $ (917.6) THREE MONTHS ENDED MARCH 31, 2023 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2022 $ (1,367.6) $ 1.2 $ 164.6 $ (367.4) $ (1,569.2) Net Change 180.2 (0.1) 22.7 0.2 203.0 Balance at March 31, 2023 $ (1,187.4) $ 1.1 $ 187.3 $ (367.2) $ (1,366.2) TABLE 58: DETAILS OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED MARCH 31, 2024 2023 (In Millions) PRE-TAX TAX AFTER TAX PRE-TAX TAX AFTER TAX Unrealized Gains (Losses) on Available for Sale Debt Securities Unrealized Gains (Losses) on Available for Sale Debt Securities $ 73.2 $ (19.4) $ 53.8 $ 229.3 $ (60.3) $ 169.0 Reclassification Adjustments for (Gains) Losses Included in Net Income: Interest Income on Debt Securities (1) 24.4 (6.2) 18.2 21.9 (5.5) 16.4 Net (Gains) Losses on Debt Securities (2) 189.4 (48.0) 141.4 (6.9) 1.7 (5.2) Net Change $ 287.0 $ (73.6) $ 213.4 $ 244.3 $ (64.1) $ 180.2 Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ 4.5 $ (1.1) $ 3.4 $ 0.5 $ (0.1) $ 0.4 Reclassification Adjustment for (Gains) Losses Included in Net Income (3) (5.5) 1.4 (4.1) (0.6) 0.1 (0.5) Net Change $ (1.0) $ 0.3 $ (0.7) $ (0.1) $ — $ (0.1) Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (58.5) $ 2.9 $ (55.6) $ 46.8 $ 0.2 $ 47.0 Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) (0.6) 0.1 (0.5) — — — Net Investment Hedge Gains (Losses) 81.3 (20.6) 60.7 (32.5) 8.2 (24.3) Net Change $ 22.2 $ (17.6) $ 4.6 $ 14.3 $ 8.4 $ 22.7 Pension and Other Postretirement Benefit Adjustments Net Actuarial Gains (Losses) $ 1.1 $ (0.5) $ 0.6 $ (1.1) $ 0.1 $ (1.0) Reclassification Adjustment for (Gains) Losses Included in Net Income (4) Amortization of Net Actuarial Loss 3.2 (0.8) 2.4 1.6 (0.4) 1.2 Net Change $ 4.3 $ (1.3) $ 3.0 $ 0.5 $ (0.3) $ 0.2 Total Net Change $ 312.5 $ (92.2) $ 220.3 $ 259.0 $ (56.0) $ 203.0 (1) The before-tax reclassification adjustment is related to the unrealized gains (losses) amortization on AFS debt securities that were transferred to HTM debt securities during the second quarter of 2021 and third quarter of 2022. (2) The net gains (losses) on AFS debt securities before-tax reclassification adjustment is recorded in Investment Security Gains (Losses), net on the consolidated statements of income. (3) See Note 21—Derivative Financial Instruments for the location of the reclassification adjustment related to cash flow hedges. (4) The pension and other postretirement benefit before-tax reclassification adjustment is recorded in Employee Benefits expense on the consolidated statements of income.

Net Income Per Common Share

Net Income Per Common Share	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Net Income Per Common Share	Net Income Per Common Share The computations of net income per common share are presented in the following table. TABLE 59: NET INCOME PER COMMON SHARE THREE MONTHS ENDED MARCH 31, ($ In Millions Except Per Common Share Information) 2024 2023 Basic Net Income Per Common Share Average Number of Common Shares Outstanding 204,628,796 208,186,841 Net Income $ 214.7 $ 334.6 Less: Dividends on Preferred Stock 16.2 16.2 Net Income Applicable to Common Stock 198.5 318.4 Less: Earnings Allocated to Participating Securities 2.4 3.2 Earnings Allocated to Common Shares Outstanding 196.1 315.2 Basic Net Income Per Common Share $ 0.96 $ 1.51 Diluted Net Income Per Common Share Average Number of Common Shares Outstanding 204,628,796 208,186,841 Plus: Dilutive Effect of Share-based Compensation 506,049 543,548 Average Common and Potential Common Shares 205,134,845 208,730,389 Earnings Allocated to Common and Potential Common Shares $ 196.1 $ 315.2 Diluted Net Income Per Common Share 0.96 1.51

Revenue from Contracts with Cli

Revenue from Contracts with Clients	3 Months Ended
	Mar. 31, 2024
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Clients	Revenue from Contracts with Clients Trust, Investment, and Other Servicing Fees. Custody and Fund Administration income is comprised of revenues received from our core asset servicing business for providing custody, fund administration, and middle-office-related services, primarily to Asset Servicing clients. Investment Management and Advisory income contains revenue received from providing asset management and related services to Wealth Management and Asset Servicing clients and to Northern Trust sponsored funds. Securities Lending income represents revenues generated from securities lending arrangements that Northern Trust enters into as agent, mainly with Asset Servicing clients. Other income largely consists of revenues received from providing employee benefit, investment risk and analytic and other services to Asset Servicing and Wealth Management clients. Other Noninterest Income. Treasury Management income represents revenues received from providing cash and liquidity management services to Asset Servicing and Wealth Management clients. The portion of Security Commissions and Trading Income that relates to revenue from contracts with clients is primarily comprised of commissions earned from providing securities brokerage services to Wealth Management and Asset Servicing clients. The portion of Other Operating Income that relates to revenue from contracts with clients is mainly comprised of service fees for banking-related services provided to Wealth Management and Asset Servicing clients. Performance Obligations. Clients are typically charged monthly or quarterly in arrears based on the fee arrangement agreed to with each client; payment terms will vary depending on the client and services offered. Substantially all revenues generated from contracts with clients for asset servicing, asset management, securities lending, treasury management and banking-related services are recognized on an accrual basis, over the period in which services are provided. The nature of Northern Trust’s performance obligations is to provide a series of distinct services in which the customer simultaneously receives and consumes the benefits of the promised services as they are performed. Fee arrangements are mainly comprised of variable amounts based on market value of client assets managed and serviced, transaction volumes, number of accounts, and securities lending volume and spreads. Revenue is recognized using the output method in an amount that reflects the consideration to which Northern Trust expects to be entitled in exchange for providing each month or quarter of service. For contracts with multiple performance obligations, revenue is allocated to each performance obligation based on the price agreed to with the client, representing its relative standalone selling price. Security brokerage revenue is primarily represented by securities commissions received in exchange for providing trade execution related services. Control is transferred at a point in time, on the trade date of the transaction, and fees are typically variable based on transaction volumes and security types. Northern Trust’s contracts with its clients are typically open-ended arrangements and are therefore considered to have an original duration of less than one year. Northern Trust has elected the practical expedient to not disclose the value of remaining performance obligations for contracts with an original expected duration of one year or less. The following table presents revenues disaggregated by major revenue source. TABLE 60: REVENUE DISAGGREGATION THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Noninterest Income Trust, Investment and Other Servicing Fees Custody and Fund Administration $ 467.4 $ 441.6 Investment Management and Advisory 593.9 540.5 Securities Lending 18.6 19.1 Other 63.0 62.4 Total Trust, Investment and Other Servicing Fees $ 1,142.9 $ 1,063.6 Other Noninterest Income Foreign Exchange Trading Income $ 57.0 $ 53.0 Treasury Management Fees 9.3 8.4 Security Commissions and Trading Income 37.9 34.7 Other Operating Income 61.0 46.8 Investment Security Gains (Losses), net (189.4) 6.9 Total Other Noninterest Income $ (24.2) $ 149.8 Total Noninterest Income $ 1,118.7 $ 1,213.4 On the consolidated statements of income, Trust, Investment and Other Servicing Fees and Treasury Management Fees represent revenue from contracts with clients. For the three months ended March 31, 2024, revenue from contracts with clients also includes $33.7 million of the $37.9 million total Security Commissions and Trading Income and $9.3 million of the $61.0 million total Other Operating Income. For the three months ended March 31, 2023, revenue from contracts with clients also includes $29.9 million of the $34.7 million total Security Commissions and Trading Income and $9.1 million of the $46.8 million total Other Operating Income. Receivables Balances. The table below represents receivables balances from contracts with clients, which are included in Other Assets on the consolidated balance sheets, at March 31, 2024 and December 31, 2023. TABLE 61: CLIENT RECEIVABLES (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Trust Fees Receivable, net (1) $ 949.4 $ 863.5 Other 47.7 64.9 Total Client Receivables $ 997.1 $ 928.4 (1) Trust Fees Receivable is net of a $14.8 million and $15.9 million fee receivable allowance as of March 31, 2024 and December 31, 2023, respectively.

Net Interest Income

Net Interest Income	3 Months Ended
	Mar. 31, 2024
Banking and Thrift, Interest [Abstract]
Net Interest Income	Net Interest Income The components of Net Interest Income were as follows. TABLE 62: NET INTEREST INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Interest Income Federal Reserve and Other Central Bank Deposits $ 459.7 $ 377.0 Interest-Bearing Due from and Deposits with Banks (1) 34.6 28.2 Federal Funds Sold — 0.2 Securities Purchased under Agreements to Resell 823.9 125.9 Securities — Taxable 445.3 337.8 — Nontaxable (2) 0.3 0.3 Loans 653.6 578.2 Other Interest-Earning Assets (3) 28.2 7.8 Total Interest Income $ 2,445.6 $ 1,455.4 Interest Expense Deposits $ 881.7 $ 564.6 Federal Funds Purchased 33.6 40.1 Securities Sold Under Agreements to Repurchase 813.9 116.1 Other Borrowings 88.6 135.0 Senior Notes 44.1 39.2 Long-Term Debt 55.6 29.2 Total Interest Expense $ 1,917.5 $ 924.2 Net Interest Income $ 528.1 $ 531.2 (1) Interest-Bearing Due from and Deposits with Banks includes the interest-bearing component of Cash and Due from Banks and Interest-Bearing Deposits with Banks as presented on the consolidated balance sheets. (2) Non-taxable Securities represent securities that are exempt from U.S. federal income taxes. (3) Other Interest-Earning Assets include certain community development investments, collateral deposits with certain securities depositories and clearing houses, Federal Home Loan Bank and Federal Reserve stock, and money market investments which are classified in Other Assets on the consolidated balance sheets.

Other Operating Income

Other Operating Income	3 Months Ended
	Mar. 31, 2024
Other Income and Expenses [Abstract]
Other Operating Income	Other Operating Income The components of Other Operating Income were as follows. TABLE 63: OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Loan Service Fees $ 15.7 $ 18.7 Banking Service Fees 13.3 12.2 Bank Owned Life Insurance 20.6 16.7 Other Income (1) 11.4 (0.8) Total Other Operating Income $ 61.0 $ 46.8 (1) Other Income includes the mark-to-market gain or loss on derivative swap activity primarily related to the sale of certain Visa Class B common shares. The components of Other Operating Expense were as follows. TABLE 64: OTHER OPERATING EXPENSE THREE MONTHS ENDED MARCH 31, In Millions) 2024 2023 Business Promotion $ 16.7 $ 16.2 Staff Related 14.2 7.8 FDIC Insurance Premiums (1) 18.7 6.2 Charitable Contributions 2.0 3.2 Other Expenses 48.8 52.2 Total Other Operating Expense $ 100.4 $ 85.6 (1)

Other Operating Expense

Other Operating Expense	3 Months Ended
	Mar. 31, 2024
Other Income and Expenses [Abstract]
Other Operating Expense	Other Operating Income The components of Other Operating Income were as follows. TABLE 63: OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Loan Service Fees $ 15.7 $ 18.7 Banking Service Fees 13.3 12.2 Bank Owned Life Insurance 20.6 16.7 Other Income (1) 11.4 (0.8) Total Other Operating Income $ 61.0 $ 46.8 (1) Other Income includes the mark-to-market gain or loss on derivative swap activity primarily related to the sale of certain Visa Class B common shares. The components of Other Operating Expense were as follows. TABLE 64: OTHER OPERATING EXPENSE THREE MONTHS ENDED MARCH 31, In Millions) 2024 2023 Business Promotion $ 16.7 $ 16.2 Staff Related 14.2 7.8 FDIC Insurance Premiums (1) 18.7 6.2 Charitable Contributions 2.0 3.2 Other Expenses 48.8 52.2 Total Other Operating Expense $ 100.4 $ 85.6 (1)

Pension

Pension	3 Months Ended
	Mar. 31, 2024
Retirement Benefits [Abstract]
Pension	Pension The following table sets forth the net periodic pension expense for Northern Trust’s U.S. Qualified Plan, Non-U.S. Pension Plans, and U.S. Non-Qualified Plan for the three months ended March 31, 2024 and 2023. TABLE 65: NET PERIODIC PENSION EXPENSE (BENEFIT) U.S. QUALIFIED PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Service Cost $ 13.4 $ 11.5 Interest Cost 13.9 13.5 Expected Return on Plan Assets (28.9) (25.3) Amortization Net Actuarial Loss 1.9 0.4 Net Periodic Pension Expense $ 0.3 $ 0.1 NON-U.S. PENSION PLANS THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Service Cost $ 0.5 $ 0.3 Interest Cost 1.1 1.2 Expected Return on Plan Assets (1.6) (1.5) Amortization Net Actuarial (Gain) — (0.1) Net Periodic Pension (Benefit) $ — $ (0.1) U.S. NON-QUALIFIED PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Service Cost $ 1.2 $ 1.2 Interest Cost 1.2 1.3 Amortization Net Actuarial Loss 1.3 1.3 Net Periodic Pension Expense $ 3.7 $ 3.8 The components of net periodic pension expense are recorded in Employee Benefits expense on the consolidated statements of income. There were $200.0 million of contributions to the U.S. Qualified Plan during the three months ended March 31, 2024. There were no contributions to the U.S. Qualified Plan during the three months ended March 31, 2023. There were $8.0 million and $16.5 million of contributions to the U.S. Non-Qualified Plan during the three months ended March 31, 2024 and 2023, respectively.

Share-Based Compensation Plans

Share-Based Compensation Plans	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Share-Based Compensation Plans	Share-Based Compensation Plans The Northern Trust Corporation 2017 Long-Term Incentive Plan provides for the grant of non-qualified and incentive stock options; tandem and free-standing stock appreciation rights; stock awards in the form of restricted stock, restricted stock units and other stock awards; and performance awards. Restricted stock unit and performance stock unit grants continue to vest in accordance with the original terms of the award if the applicable employee retires after satisfying applicable age and service requirements. The Corporation granted 1,086,910 stock units awards with a total grant-date fair value of $86.0 million during the three months ended March 31, 2024, compared to 1,029,713 stock units awards with a total grant-date fair value of $95.9 million during the three months ended March 31, 2023. Compensation expense for the three months ended March 31, 2024 included $28.8 million attributable to restricted stock units granted to retirement-eligible employees that were expensed in their entirety on the date of grant, compared to $31.4 million in the prior-year quarter. The Corporation granted 262,557 performance stock units with a total grant-date fair value of $21.0 million during the three months ended March 31, 2024, compared to 219,314 performance stock units with a total grant-date fair value of $20.6 million during the three months ended March 31, 2023. Compensation expense for the three months ended March 31, 2024 included $12.8 million attributable to performance stock units granted to retirement-eligible employees that were expensed in their entirety on the date of grant, compared to $14.2 million in the prior-year quarter. Restricted stock unit award compensation expense for the three months ended March 31, 2024 and 2023 included $4.5 million and $4.2 million, respectively, attributable to restricted stock units vested in full and expensed in their entirety upon date of grant. Total compensation expense for share-based payment arrangements and the associated tax impacts were as follows for the three months ended March 31, 2024 and 2023. TABLE 66: TOTAL COMPENSATION EXPENSE FOR SHARE-BASED PAYMENT ARRANGEMENTS THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Restricted Stock Unit Awards $ 49.4 $ 50.3 Performance Stock Units 17.0 14.1 Total Share-Based Compensation Expense 66.4 64.4 Tax Benefits Recognized $ 16.8 $ 16.2

Variable Interest Entities

Variable Interest Entities	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	Variable Interest Entities Northern Trust is involved with various entities in the normal course of business that are deemed to be variable interest entities (VIEs). VIEs are defined within GAAP as entities which either (1) lack sufficient equity at risk to permit the entity to finance its activities without additional subordinated financial support, (2) have equity investors that lack attributes typical of an equity investor, such as the ability to make significant decisions through voting rights affecting the entity’s operations, or the obligation to absorb expected losses or the right to receive residual returns of the entity, or (3) are structured with voting rights that are disproportionate to the equity investor’s obligation to absorb losses or right to receive returns, and substantially all of the activities are conducted on behalf of the holder of the equity investment at risk with disproportionately few voting rights. Investors that finance a VIE through debt or equity interests are variable interest holders in the entity and the variable interest holder, if any, that has both the power to direct the activities that most significantly impact the entity’s economic performance and, through its variable interest, the obligation to absorb losses or the right to receive returns that could potentially be significant to the entity is deemed to be the VIE’s primary beneficiary and is required to consolidate the VIE. Tax credit structures. Northern Trust holds tax-advantaged investments in unconsolidated entities that own and operate affordable housing and projects through the new markets tax credit program. These entities, which are limited partnerships and similar entities, are primarily VIEs and are designed to generate a return primarily through the realization of tax credits and other tax benefits, such as tax deductions from operating losses of the investments. Northern Trust invests as a limited partner/investor member and lacks both the power to direct the entities’ most significant activities and the obligation to absorb losses or right to receive benefits that could potentially be significant to the entities. Northern Trust is not required to consolidate these entities as it does not have a controlling financial interest and thus is not the primary beneficiary. Northern Trust’s maximum exposure to loss as a result of its involvement with these entities is limited to the carrying amounts of its investments, including any undrawn commitments. Northern Trust’s funding requirements are limited to its invested capital and undrawn commitments for future equity contributions. Northern Trust has no exposure to loss from liquidity arrangements and no obligation to purchase assets of these entities. Northern Trust’s investments in these unconsolidated entities and related unfunded commitments are reported in Other Assets and Other Liabilities, respectively, on the consolidated balance sheets. TABLE 67: SUMMARY OF UNCONSOLIDATED TAX CREDIT STRUCTURES (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Investment Carrying Amount Affordable Housing $ 603.3 $ 622.8 New Markets 263.1 266.3 Total Investment Carrying Amount (1) $ 866.4 $ 889.1 Unfunded Commitments Affordable Housing $ 163.3 $ 178.8 New Markets — — Total Unfunded Commitments (2) $ 163.3 $ 178.8 (1) As of March 31, 2024 and December 31, 2023, $835.7 million and $857.0 million are VIEs, respectively. (2) As of March 31, 2024 and December 31, 2023, $156.6 million and $172.0 million relate to undrawn commitments on VIEs, respectively. Upon adoption of ASU 2023-02 on January 1, 2024, Northern Trust elected to account for qualifying new markets tax credit investments under the proportional amortization method. Prior to the adoption of ASU 2023-02, Northern Trust accounted for qualifying affordable housing investments under the proportional amortization method and continues to do so subsequent to the adoption of ASU 2023-02. Under the proportional amortization method, the carrying amount of the investment is amortized in proportion to the income tax credits and other income tax benefits received in the current period as compared to the total income tax credits and income tax benefits expected to be received over the life of the investment. Income tax credits and other income tax benefits and amortization expense associated with unconsolidated tax credit structures are primarily reported in the Provision for Income Tax on the consolidated statement of income. Northern Trust adopted ASU 2023-02 on a modified retrospective basis. As a result, amortization expense related to new markets tax credit investments is reported in the Provision for Income Tax beginning January 1, 2024. Prior to January 1, 2024, amortization expense related to new markets tax credit investments was previously reported in Other Operating Expense. Refer to Note 2—Recent Accounting Pronouncements for additional information. TABLE 68: INCOME TAX CREDITS AND OTHER TAX BENEFITS AND AMORTIZATION EXPENSE ASSOCIATED WITH TAX CREDIT STRUCTURES (In Millions) MARCH 31, 2024 MARCH 31, 2023 Income Tax Credits and Other Income Tax Benefits Affordable Housing $ 21.7 $ 22.4 New Markets 5.0 5.9 Total Income Tax Credits and Other Income Tax Benefits $ 26.7 $ 28.3 Amortization Expense Affordable Housing $ 19.5 $ 19.8 New Markets 4.4 4.7 Total Amortization Expense $ 23.9 $ 24.5 Investment funds. Northern Trust acts as asset manager for various funds in which clients of Northern Trust are investors. As an asset manager of funds, Northern Trust earns a competitively priced fee that is based on assets managed and varies with each fund’s investment objective. Based on its analysis, Northern Trust has determined that it is not the primary beneficiary of these VIEs under GAAP. Some of the funds for which Northern Trust acts as asset manager comply or operate in accordance with requirements that are similar to those in Rule 2a-7 of the Investment Company Act of 1940 for registered money market funds and, therefore, the funds are exempt from the consolidation requirements in ASC 810-10. Northern Trust voluntarily waived $2.3 million and $2.0 million of money market fund fees for the three months ended March 31, 2024 and 2023, respectively, related to certain competitive factors. Northern Trust does not have any contractual obligations to provide financial support to the funds. Any potential future support of the funds will be at the discretion of Northern Trust after an evaluation of the specific facts and circumstances.

Commitments and Contingent Liab

Commitments and Contingent Liabilities	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingent Liabilities	Commitments and Contingent Liabilities Off-Balance Sheet Financial Instruments, Guarantees and Other Commitments. Northern Trust, in the normal course of business, enters into various types of commitments and issues letters of credit to meet the liquidity and credit enhancement needs of its clients. The contractual amounts of these instruments represent the maximum potential credit exposure should the instrument be fully drawn upon and the client default. To control the credit risk associated with entering into commitments and issuing letters of credit, Northern Trust subjects such activities to the same credit quality and monitoring controls as its lending activities. Northern Trust does not believe the total contractual amount of these instruments to be representative of its future credit exposure or funding requirements. The following table provides details of Northern Trust's off-balance sheet financial instruments as of March 31, 2024 and December 31, 2023. TABLE 69: SUMMARY OF OFF-BALANCE SHEET FINANCIAL INSTRUMENTS MARCH 31, 2024 DECEMBER 31, 2023 (In Millions) ONE YEAR AND LESS OVER ONE YEAR TOTAL ONE YEAR AND LESS OVER ONE YEAR TOTAL Undrawn Commitments (1) $ 10,322.2 $ 18,957.1 $ 29,279.3 $ 11,849.5 $ 18,909.6 $ 30,759.1 Standby Letters of Credit and Financial Guarantees (2)(3) 90,610.8 327.2 90,938.0 85,752.0 639.0 86,391.0 Commercial Letters of Credit 17.2 0.1 17.3 29.2 1.3 30.5 Securities Lent with Indemnification 138,278.1 — 138,278.1 140,539.1 — 140,539.1 Unsettled Reverse Repurchase Agreements 16,442.4 — 16,442.4 27,667.7 — 27,667.7 Total Off-Balance Sheet Financial Instruments $ 255,670.7 $ 19,284.4 $ 274,955.1 $ 265,837.5 $ 19,549.9 $ 285,387.4 (1) These amounts exclude $259.1 million and $222.2 million of commitments participated to others at March 31, 2024 and December 31, 2023, respectively. (2) These amounts include $41.0 million and $39.1 million of standby letters of credit secured by cash deposits or participated to others as of March 31, 2024 and December 31, 2023, respectively. (3) These amounts include a $89.3 billion and $84.6 billion guarantee to the Fixed Income Clearing Corporation (FICC) under the sponsored member program, without taking into consideration the related collateral, as of March 31, 2024 and December 31, 2023, respectively. Northern Trust became a sponsored member during the third quarter of 2021. Undrawn Commitments generally have fixed expiration dates or other termination clauses. Since a significant portion of the commitments are expected to expire without being drawn upon, the total commitment amount does not necessarily represent future loans or liquidity requirements. Standby Letters of Credit obligate Northern Trust to meet certain financial obligations of its clients, if, under the contractual terms of the agreement, the clients are unable to do so. These instruments are primarily issued to support public and private financial commitments, including commercial paper, bond financing, initial margin requirements on futures exchanges and similar transactions. Northern Trust is obligated to meet the entire financial obligation of these agreements and in certain cases is able to recover the amounts paid through recourse against collateral received or other participants. Since the vast majority of the standby letters of credit are never drawn, the total standby letters of credit amount does not necessarily represent future loans or liquidity requirements. Financial Guarantees are issued by Northern Trust to guarantee the performance of a client to a third party under certain arrangements. Commercial Letters of Credit are instruments issued by Northern Trust on behalf of its clients that authorize a third party (the beneficiary) to draw drafts up to a stipulated amount under the specified terms and conditions of the agreement and other similar instruments. Commercial letters of credit are issued primarily to facilitate international trade. Securities Lent with Indemnification involves Northern Trust lending securities owned by clients to borrowers who are reviewed and approved by the Northern Trust Capital Markets Credit Committee, as part of its securities custody activities and at the direction of its clients. In connection with these activities, Northern Trust has issued indemnifications to certain clients against certain losses that are a direct result of a borrower’s failure to return securities when due, should the value of such securities exceed the value of the collateral required to be posted. Borrowers are required to collateralize fully securities received with cash or marketable securities. As securities are loaned, collateral is maintained at a minimum of 100% of the fair value of the securities plus accrued interest. The collateral is revalued on a daily basis. The amount of securities loaned as of March 31, 2024 and December 31, 2023 subject to indemnification was $138.3 billion and $140.5 billion, respectively. Because of the credit quality of the borrowers and the requirement to fully collateralize securities borrowed, management believes that the exposure to credit loss from this activity is not significant and no liability was recorded as of March 31, 2024 or December 31, 2023, related to these indemnifications. Unsettled Repurchase and Reverse Repurchase Agreements. Northern Trust enters into repurchase agreements and reverse repurchase agreements which may settle at a future date. In repurchase agreements, Northern Trust receives cash from and provides securities as collateral to a counterparty. In reverse repurchase agreements, Northern Trust advances cash to and receives securities as collateral from a counterparty. These transactions are recorded on the consolidated balance sheets on the settlement date. As of March 31, 2024 and December 31, 2023, there were $16.4 billion and $27.7 billion unsettled reverse repurchase agreements, respectively, and no unsettled repurchase agreements. Sponsored Member Program . Northern Trust is an approved Government Securities Division (GSD) netting and sponsoring member in the FICC sponsored member program, through which Northern Trust submits eligible repurchase and reverse repurchase transactions in U.S. government securities between Northern Trust and its sponsored member clients for novation and clearing. Northern Trust may sponsor clients to clear their eligible repurchase transactions with the FICC. As a sponsoring member, Northern Trust guarantees to the FICC the prompt and full payment and performance of its sponsored member clients’ respective obligations under the FICC GSD’s rules. To mitigate Northern Trust’s credit exposure under this guarantee, Northern Trust obtains a security interest in its sponsored member clients’ collateral. See Note 23—Offsetting of Assets and Liabilities for additional information on Northern Trust’s repurchase and reverse repurchase agreements. Clearing and Settlement Organizations . The Bank is a participating member of various cash, securities and foreign exchange clearing and settlement organizations. It participates in these organizations on behalf of its clients and on its own behalf as a result of its own activities. A wide variety of cash and securities transactions are settled through these organizations, including those involving U.S. Treasuries, obligations of states and political subdivisions, asset-backed securities, commercial paper, dollar placements, and securities issued by the Government National Mortgage Association. Certain of these industry clearing and settlement exchanges require their members to guarantee their obligations and liabilities and/or to provide liquidity support in the event other members do not honor their obligations as stipulated in each clearing organization’s membership agreement. Exposure related to these agreements varies, primarily as a result of fluctuations in the volume of transactions cleared through the organizations. At March 31, 2024 and December 31, 2023, Northern Trust has not recorded any material liabilities under these arrangements as Northern Trust believes the likelihood that a clearing or settlement exchange (of which Northern Trust is a member) would become insolvent is remote. Controls related to these clearing transactions are closely monitored by management to protect the assets of Northern Trust and its clients. FDIC Special Assessment . In November 2023, the Federal Deposit Insurance Corporation (FDIC) issued a final rule to implement a special assessment to recoup losses to the deposit insurance fund associated with bank failures in the first half of 2023. In conjunction with the special assessment, $84.6 million was recognized as an accrued liability and related expense in the fourth quarter of 2023. During the current quarter, the FDIC published revised estimated losses as well as estimated recoveries from the related bank failures As a result, Northern Trust estimated an additional cost of $12.5 million in the current quarter, recorded to Other Operating Expense. Legal Proceedings. In the normal course of business, the Corporation and its subsidiaries are routinely defendants in or parties to pending and threatened legal actions, and are subject to regulatory examinations, information-gathering requests, investigations, and proceedings, both formal and informal. In certain legal actions, claims for substantial monetary damages are asserted. In regulatory matters, claims for disgorgement, restitution, penalties and/or other remedial actions or sanctions may be sought. Based on current knowledge, after consultation with legal counsel and after taking into account current accruals, management does not believe that losses, fines or penalties, if any, arising from pending litigation or threatened legal actions or regulatory matters either individually or in the aggregate, after giving effect to applicable reserves and insurance coverage will have a material adverse effect on the consolidated financial position or liquidity of the Corporation, although such matters could have a material adverse effect on the Corporation’s operating results for a particular period. Under GAAP, (i) an event is “probable” if the “future event or events are likely to occur”; (ii) an event is “reasonably possible” if “the chance of the future event or events occurring is more than remote but less than likely”; and (iii) an event is “remote” if “the chance of the future event or events occurring is slight.” The outcome of litigation and regulatory matters is inherently difficult to predict and/or the range of loss often cannot be reasonably estimated, particularly for matters that (i) will be decided by a jury, (ii) are in early stages, (iii) involve uncertainty as to the likelihood of a class being certified or the ultimate size of the class, (iv) are subject to appeals or motions, (v) involve significant factual issues to be resolved, including with respect to the amount of damages, (vi) do not specify the amount of damages sought or (vii) seek very large damages based on novel and complex damage and liability legal theories. Accordingly, the Corporation cannot reasonably estimate the eventual outcome of these pending matters, the timing of their ultimate resolution or what the eventual loss, fines or penalties, if any, related to each pending matter will be. In accordance with applicable accounting guidance, the Corporation records accruals for litigation and regulatory matters when those matters present loss contingencies that are both probable and reasonably estimable. When loss contingencies are not both probable and reasonably estimable, the Corporation does not record accruals. No material accruals have been recorded for pending litigation or threatened legal actions or regulatory matters. For a limited number of matters for which a loss is reasonably possible in future periods, whether in excess of an accrued liability or where there is no accrued liability, the Corporation is able to estimate a range of possible loss. As of March 31, 2024, the Corporation has estimated the range of reasonably possible loss for these matters to be from zero to approximately $25 million in the aggregate. The Corporation’s estimate with respect to the aggregate range of reasonably possible loss is based upon currently available information and is subject to significant judgment and a variety of assumptions and known and unknown uncertainties. The matters underlying the estimated range will change from time to time, and actual results may vary significantly from the current estimate. In certain other pending matters, there may be a range of reasonably possible loss (including reasonably possible loss in excess of amounts accrued) that cannot be reasonably estimated for the reasons described above. Such matters are not included in the estimated range of reasonably possible loss discussed above. In 2015, Northern Trust Fiduciary Services (Guernsey) Limited (NTFS), an indirect subsidiary of the Corporation, was charged by a French investigating magistrate judge with complicity in estate tax fraud in connection with the administration of two trusts for which it serves as trustee. Charges also were brought against a number of other persons and entities related to this matter. In 2017, a French court found no estate tax fraud had occurred and NTFS and all other persons and entities charged were acquitted. The Public Prosecutor’s Office of France appealed the court decision and in June 2018 a French appellate court issued its opinion on the matter, acquitting all persons and entities charged, including NTFS. In January 2021, the Cour de Cassation, the highest court in France, reversed the June 2018 appellate court ruling, requiring a re-trial at the appellate court level. This re-trial concluded in October 2023. On March 5, 2024 the appellate court rendered a judgment against all defendants, including NTFS. NTFS was ordered to pay a fine of €187,500 in conjunction with the judgment. In addition, the court ordered that certain of those convicted in relation to tax fraud or aiding and abetting tax fraud, including NTFS, are jointly and severally liable for any allegedly unpaid estate taxes owing, plus penalties and interest. NTFS provided no tax advice and was not involved in the preparation or filing of the challenged estate tax filings in this case. Further, NTFS believes it acted in accordance with all applicable laws and fully complied with its fiduciary duties. Accordingly, NTFS filed an appeal of the judgment on March 5, 2024. Under applicable law, upon the filing by NTFS of its appeal, the judgment, as well as its effects (including the fine and joint and several liability) will be stayed pending the outcome of the appeal. Visa Class B Common Shares. Northern Trust, as a member of Visa U.S.A. Inc. (Visa U.S.A.) and in connection with the 2007 restructuring of Visa U.S.A. and its affiliates and the 2008 initial public offering of Visa Inc. (Visa), received certain Visa Class B common shares. The Visa Class B common shares are subject to certain transfer restrictions until the final resolution of certain litigation related to interchange fees involving Visa (the covered litigation), at which time the shares are convertible into Visa Class A common shares based on a conversion rate dependent upon the ultimate cost of resolving the covered litigation. Since 2018, Visa has deposited an additional $2.8 billion into an escrow account previously established with respect to the covered litigation. As a result of the additional contributions to the escrow account, the rate at which Visa Class B common shares will convert into Visa Class A common shares was reduced to 1.5875 as of March 31, 2024. In September 2018, Visa reached a proposed class settlement agreement covering damage claims but not injunctive relief claims regarding the covered litigation. In December 2019, the district court granted final approval for the proposed class settlement agreement. In March 2023, the Second Circuit Court of Appeals affirmed the district court’s approval of the class settlement agreement. Certain merchants have opted out of the class settlement and are pursuing claims separately. In March 2024, Visa announced it reached a settlement agreement covering injunctive relief claims regarding the covered litigation, this settlement is subject to court approval. The ultimate resolution of the covered litigation, the timing for removal of the selling restrictions on the Visa Class B common shares and the rate at which such shares will ultimately convert into Visa Class A common shares are uncertain. On April 8, 2024, Visa commenced an offer to exchange outstanding shares of its Class B common stock (Exchange Offer). Under the Exchange Offer, Visa Class B common shareholders have the option to tender some or all of their Class B common shares and in return receive shares of a newly issued series of Visa Class B common shares with a value equal to half the value of the tendered shares and Visa Class C common shares with value equal to the other half of the tendered shares. The newly issued series of Visa Class B common shares are subject to the same transfer and convertibility restrictions as the currently outstanding Visa Class B common shares. The Visa Class C common shares will automatically be converted at the then applicable conversion rate into shares of Visa Class A common stock if transferred to a person other than a Visa member or an affiliate of a Visa member. One third of the Visa Class C common shares received are transferable within the first 45 days following the accepted exchange, up to two-thirds are transferable within the first 90 days, and all such shares are transferable after 90 days. After the initial exchange offer, Visa can, at its discretion, conduct up to three successive potential exchange offers, in each case, if more than 12 months have passed since the previous exchange offer and after a further 50% reduction of interchange fees at issue in the unresolved claims for damages in the covered litigation. Northern Trust has submitted its election to participate in the Exchange Offer and is tendering all of the Class B shares that it currently holds. In June 2016 and 2015, Northern Trust recorded a $123.1 million and $99.9 million net gain on the sale of 1.1 million and 1.0 million of its Visa Class B common shares, respectively. These sales do not affect Northern Trust’s risk related to the impact of the covered litigation on the rate at which such shares will ultimately convert into Visa Class A common shares. Northern Trust continued to hold approximately 4.1 million Visa Class B common shares, which are recorded at their original cost basis of zero, as of March 31, 2024 and December 31, 2023. Based upon the March 28, 2024, closing price of $279.08 for a Visa Class A common share, the estimated value of Northern Trust’s Visa Class B shares was approximately $1.8 billion at the current conversion rate of Visa Class B to Visa Class A common shares. The estimated value does not represent fair value given the shares’ limited transferability.

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments Northern Trust is a party to various derivative financial instruments that are used in the normal course of business to meet the needs of its clients, as part of its trading activity for its own account and as part of its risk management activities. These instruments may include foreign exchange contracts, interest rate contracts, total return swap contracts, and swaps related to the sale of certain Visa Class B common shares. Foreign exchange contracts are agreements to exchange specific amounts of currencies at a future date, at a specified rate of exchange. Foreign exchange contracts are entered into primarily to meet the foreign exchange needs of clients. Foreign exchange contracts are also used for trading and risk management purposes. For risk management purposes, Northern Trust uses foreign exchange contracts to reduce its exposure to changes in foreign exchange rates relating to certain forecasted non-functional-currency-denominated revenue and expenditure transactions, foreign-currency-denominated assets and liabilities, including debt securities, and net investments in non-U.S. affiliates. Interest rate contracts include swap and option contracts. Interest rate swap contracts involve the exchange of fixed and floating rate interest payment obligations without the exchange of the underlying principal amounts. Northern Trust enters into interest rate swap contracts with its clients and also may utilize such contracts to reduce or eliminate the exposure to changes in the cash flows or fair value of hedged assets or liabilities due to changes in interest rates. Interest rate option contracts may include caps, floors, collars and swaptions, and provide for the transfer or reduction of interest rate risk, typically in exchange for a fee. Northern Trust enters into option contracts primarily as a seller of interest rate protection to clients. Northern Trust receives a fee at the outset of the agreement for the assumption of the risk of an unfavorable change in interest rates. This assumed interest rate risk is then mitigated by entering into an offsetting position with an outside counterparty. Northern Trust may also purchase or enter into option contracts for risk management purposes including to reduce the exposure to changes in the cash flows of hedged assets due to changes in interest rates. The following table shows the notional and fair values of all derivative financial instruments as of March 31, 2024 and December 31, 2023. TABLE 70: NOTIONAL AND FAIR VALUES OF DERIVATIVE FINANCIAL INSTRUMENTS MARCH 31, 2024 DECEMBER 31, 2023 NOTIONAL VALUE FAIR VALUE NOTIONAL VALUE FAIR VALUE (In Millions) ASSET (1) LIABILITY (2) ASSET (1) LIABILITY (2) Derivatives Designated as Hedging under GAAP Interest Rate Contracts Fair Value Hedges $ 9,466.4 $ 182.4 $ 420.1 $ 7,042.7 $ 94.7 $ 71.0 Foreign Exchange Contracts Cash Flow Hedges 164.9 4.0 — 1,453.6 15.0 42.2 Net Investment Hedges 4,086.7 21.2 0.8 4,077.4 13.3 31.9 Total Derivatives Designated as Hedging under GAAP $ 13,718.0 $ 207.6 $ 420.9 $ 12,573.7 $ 123.0 $ 145.1 Derivatives Not Designated as Hedging under GAAP Non-Designated Risk Management Derivatives Foreign Exchange Contracts $ — $ — $ — $ 20.7 $ — $ 0.1 Other Financial Derivatives (3) 930.4 — 21.0 867.9 — 25.4 Total Non-Designated Risk Management Derivatives $ 930.4 $ — $ 21.0 $ 888.6 $ — $ 25.5 Client-Related and Trading Derivatives Foreign Exchange Contracts $ 317,051.6 $ 1,331.9 $ 1,317.3 $ 313,336.9 $ 3,238.4 $ 3,181.0 Interest Rate Contracts 15,892.9 221.6 57.8 13,584.1 206.8 298.2 Total Client-Related and Trading Derivatives $ 332,944.5 $ 1,553.5 $ 1,375.1 $ 326,921.0 $ 3,445.2 $ 3,479.2 Total Derivatives Not Designated as Hedging under GAAP $ 333,874.9 $ 1,553.5 $ 1,396.1 $ 327,809.6 $ 3,445.2 $ 3,504.7 Total Gross Derivatives $ 347,592.9 $ 1,761.1 $ 1,817.0 $ 340,383.3 $ 3,568.2 $ 3,649.8 Less: Netting (4) 914.2 1,070.1 3,126.7 2,205.4 Total Derivative Financial Instruments $ 846.9 $ 746.9 $ 441.5 $ 1,444.4 (1) Derivative assets are reported in Other Assets on the consolidated balance sheets. (2) Derivative liabilities are reported in Other Liabilities on the consolidated balance sheets. (3) Includes swaps related to sales of certain Visa Class B common shares. (4) See further detail in Note 23—Offsetting of Assets and Liabilities. Notional amounts of derivative financial instruments do not represent credit risk and are not recorded in the consolidated balance sheets. They are used merely to express the volume of this activity. Northern Trust’s credit-related risk of loss is limited to the positive fair value of the derivative instrument, net of any collateral received, which is significantly less than the notional amount. All derivative financial instruments, whether designated as hedges or not, are recorded on the consolidated balance sheets at fair value within Other Assets or Other Liabilities. Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. Hedging Derivative Instruments Designated under GAAP. Northern Trust uses derivative instruments to hedge its exposure to foreign currency, interest rate, and equity price. Certain hedging relationships are formally designated and qualify for hedge accounting under GAAP as fair value, cash flow or net investment hedges. Other derivatives that are entered into for risk management purposes as economic hedges are not formally designated as hedges and changes in fair value are recognized currently in Other Operating Income within the consolidated statements of income (see below section “Derivative Instruments Not Designated as Hedging under GAAP”). In order to qualify for hedge accounting, a formal assessment is performed on a calendar-quarter basis to verify that derivatives used in designated hedging transactions continue to be highly effective in offsetting the changes in fair value or cash flows of the hedged item. If a derivative ceases to be highly effective, matures, is sold or is terminated, or if a hedged forecasted transaction is no longer probable of occurring, hedge accounting is terminated and the derivative is treated as if it were a trading instrument. Fair Value Hedges. Derivatives are designated as fair value hedges to limit Northern Trust’s exposure to changes in the fair value of assets and liabilities due to movements in interest rates. Northern Trust may enter into interest rate swaps to hedge changes in fair value of AFS debt securities and long-term subordinated debt and senior notes. Northern Trust applied the “shortcut” method of accounting, available under GAAP, which assumes there is perfect effectiveness in a hedge, for all of its fair value hedges during the three month periods ended March 31, 2024 and 2023. Changes in the fair value of the derivative instrument and changes in the fair value of the hedged asset or liability attributable to the hedged risk are recognized currently in earnings within the same income statement line item. Cash Flow Hedges. Derivatives are also d esignated as cash flow hedges in order to minimize the variability in cash flows of earning assets or forecasted transactions caused by movements in interest or foreign exchange rates. Northern Trust may enter into foreign exchange contracts to hedge changes in cash flows due to movements in foreign exchange rates of forecasted foreign- currency-denominated transactions and foreign-currency-denominated debt securities. Northern Trust may also enter into interest rate contracts to hedge changes in cash flows due to movements in interest rates of AFS debt securities. The change in fair value of cash flow hedging derivative instruments are recorded in AOCI and reclassified to earnings when the hedged forecasted transaction impacts earnings within the same income statement line item. There were no material gains or losses reclassified into earnings during the three month periods ended March 31, 2024 and 2023, as a result of the discontinuance of forecasted transactions that were no longer probable of occurring. It is estimated that net gains of $4.0 million will be reclassified into Net Income within the next twelve months relating to cash flow hedges of foreign-currency-denominated debt securities. As of March 31, 2024, one month was the maximum length of time over which the exposure to variability in future cash flows of forecasted foreign-currency-denominated debt securities was being hedged. The following tables provide fair value and cash flow hedge derivative gains and losses recognized in income during the three month periods ended March 31, 2024 and 2023. TABLE 71: LOCATION AND AMOUNT OF FAIR VALUE AND CASH FLOW HEDGE DERIVATIVE GAINS AND LOSSES RECORDED IN INCOME (In Millions) INTEREST INCOME INTEREST EXPENSE OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, 2024 2023 2024 2023 2024 2023 Total amounts on the consolidated statements of income $ 2,445.6 $ 1,455.4 $ 1,917.5 $ 924.2 $ 61.0 $ 46.8 Gains (Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives 123.0 (18.5) (30.1) 49.1 — — Recognized on hedged items (123.0) 18.5 30.1 (49.1) — — Amounts related to interest settlements on derivatives 22.3 12.3 (19.9) (18.4) — — Total gains (losses) recognized on fair value hedges $ 22.3 $ 12.3 $ (19.9) $ (18.4) $ — $ — Gains (Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gains (losses) reclassified from AOCI to net income $ 5.5 $ — $ — $ — $ — $ 0.6 Total gains (losses) reclassified from AOCI to net income on cash flow hedges $ 5.5 $ — $ — $ — $ — $ 0.6 The following table provides the impact of fair value hedge accounting on the carrying value of the designated hedged items as of March 31, 2024 and December 31, 2023. TABLE 72: HEDGED ITEMS IN FAIR VALUE HEDGES MARCH 31, 2024 DECEMBER 31, 2023 (In Millions) CARRYING VALUE OF THE HEDGED ITEMS CUMULATIVE HEDGE ACCOUNTING BASIS ADJUSTMENT (1)(3) CARRYING VALUE OF THE HEDGED ITEMS CUMULATIVE HEDGE ACCOUNTING BASIS ADJUSTMENT (2)(3) Available for Sale Debt Securities (4) $ 7,319.0 $ (45.5) $ 5,048.8 $ 77.5 Senior Notes and Long-Term Subordinated Debt 2,469.9 (274.8) 2,495.9 (248.7) (1) The cumulative hedge accounting basis adjustment includes $2.1 million related to discontinued hedging relationships of AFS debt securities and $25.6 million related to discontinued hedging relationships in the cumulative hedge accounting basis adjustment of senior notes and long-term debt as of March 31, 2024. (2) The cumulative hedge accounting basis adjustment includes $2.2 million related to discontinued hedging relationships of AFS debt securities and $29.6 million related to discontinued hedging relationships in the cumulative hedge accounting basis adjustment of senior notes and long-term debt as of December 31, 2023. (3) Positive (negative) amounts related to AFS securities represent cumulative fair value hedge basis adjustments that will reduce (increase) net interest income in future periods. Positive (negative) amounts related to Senior Notes and Long-Term Subordinated Debt represent cumulative fair value hedge basis adjustments that will increase (reduce) net interest income in future periods. (4) Carrying value represents amortized cost. Net Investment Hedges. Certain foreign exchange contracts are designated as net investment hedges to minimize Northern Trust’s exposure to variability in the foreign currency translation of net investments in non-U.S. branches and subsidiaries. Net investment hedge gains of $81.3 million and losses of $32.5 million were recognized in AOCI related to foreign exchange contracts for the three months ended March 31, 2024 and 2023, respectively. Derivative Instruments Not Designated as Hedging under GAAP. Northern Trust’s derivative instruments that are not designated as hedging under GAAP include derivatives for purposes of client-related and trading activities, as well as other risk management purposes. These activities consist principally of providing foreign exchange services to clients in connection with Northern Trust’s global custody business. However, in the normal course of business, Northern Trust also engages in trading of currencies for its own account. Non-designated risk management derivatives may include foreign exchange contracts entered into to manage the foreign currency risk of non-U.S.-dollar-denominated assets and liabilities, the net investment in certain non-U.S. affiliates, commercial loans and forecasted foreign-currency-denominated transactions. Swaps related to sales of certain Visa Class B common shares were entered into pursuant to which Northern Trust retains the risks associated with the ultimate conversion of the Visa Class B common shares into Visa Class A common shares. Total return swaps are entered into to manage the equity price risk associated with certain investments. Changes in the fair value of derivative instruments not designated as hedges under GAAP are recognized currently in income. The following table provides the location and amount of gains and losses recorded in the consolidated statements of income for the three and three months ended March 31, 2024 and 2023 for derivative instruments not designated as hedges under GAAP. TABLE 73: LOCATION AND AMOUNT OF GAINS AND LOSSES RECORDED IN INCOME FOR DERIVATIVES NOT DESIGNATED AS HEDGING UNDER GAAP (In Millions) DERIVATIVE GAINS (LOSSES) LOCATION RECOGNIZED IN INCOME AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME THREE MONTHS ENDED MARCH 31, 2024 2023 Non-designated risk management derivatives Foreign Exchange Contracts Other Operating Income $ (0.2) $ 0.7 Other Financial Derivatives (1) Other Operating Income (1.2) (8.8) Gains (Losses) from non-designated risk management derivatives $ (1.4) $ (8.1) Client-related and trading derivatives Foreign Exchange Contracts Foreign Exchange Trading Income $ 57.0 $ 53.0 Interest Rate Contracts Security Commissions and Trading Income 1.2 2.5 Gains from client-related and trading derivatives $ 58.2 $ 55.5 Total gains from derivatives not designated as hedging under GAAP $ 56.8 $ 47.4 (1) Includes swaps related to the sale of certain Visa Class B common shares.

Securities Sold Under Agreement

Securities Sold Under Agreements to Repurchase	3 Months Ended
	Mar. 31, 2024
Banking and Thrift, Other Disclosure [Abstract]
Securities Sold Under Agreements to Repurchase	Securities Sold Under Agreements to Repurchase Securities sold under agreements to repurchase are accounted for as collateralized financings and recorded at the amounts at which the securities were sold plus accrued interest. To minimize any potential credit risk associated with these transactions, the fair value of the securities sold is monitored, limits are set on exposure with counterparties, and the financial condition of counterparties is regularly assessed. Securities sold under agreements to repurchase are either directly held by, or pledged to the counterparty until the repurchase. Northern Trust nets securities sold under repurchase agreements against those purchased under resale agreements when there is a legally enforceable master netting arrangement and the other conditions to net are met. The following table provides information regarding repurchase agreements that are accounted for as secured borrowings as of March 31, 2024 and December 31, 2023. TABLE 74: REPURCHASE AGREEMENTS ACCOUNTED FOR AS SECURED BORROWINGS REMAINING CONTRACTUAL MATURITY OF THE AGREEMENTS MARCH 31, 2024 DECEMBER 31, 2023 (In Millions) OVERNIGHT AND CONTINUOUS U.S. Treasury and Agency Securities $ 511.4 $ 784.7 Total Borrowings 511.4 784.7 Net Amount of Recognized Liabilities for Repurchase Agreements in Note 23 511.4 784.7

Offsetting of Assets and Liabil

Offsetting of Assets and Liabilities	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Offsetting of Assets and Liabilities	Offsetting of Assets and Liabilities The following table provides information regarding the offsetting of derivative assets and securities purchased under agreements to resell within the consolidated balance sheets as of March 31, 2024 and December 31, 2023. TABLE 75: OFFSETTING OF DERIVATIVE ASSETS AND SECURITIES PURCHASED UNDER AGREEMENTS TO RESELL MARCH 31, 2024 (In Millions) GROSS RECOGNIZED ASSETS GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (3) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET (4) NET AMOUNT (5) Derivative Assets (1) Foreign Exchange Contracts Over the Counter (OTC) $ 923.3 $ 699.0 $ 224.3 $ 3.6 $ 220.7 Interest Rate Swaps OTC 399.5 215.2 184.3 — 184.3 Interest Rate Swaps Exchange Cleared 4.5 — 4.5 — 4.5 Total Derivatives Subject to a Master Netting Arrangement 1,327.3 914.2 413.1 3.6 409.5 Total Derivatives Not Subject to a Master Netting Arrangement 433.8 — 433.8 — 433.8 Total Derivatives 1,761.1 914.2 846.9 3.6 843.3 Securities Purchased under Agreements to Resell (2) $ 66,364.6 $ 65,864.5 $ 500.1 $ 500.1 $ — DECEMBER 31, 2023 (In Millions) GROSS RECOGNIZED ASSETS GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (3) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET (4) NET AMOUNT (5) Derivative Assets (1) Foreign Exchange Contracts OTC $ 3,006.3 $ 2,937.2 $ 69.1 $ 12.2 $ 56.9 Interest Rate Swaps OTC 301.4 189.5 111.9 — 111.9 Interest Rate Swaps Exchange Cleared 0.1 — 0.1 — 0.1 Total Derivatives Subject to a Master Netting Arrangement 3,307.8 3,126.7 181.1 12.2 168.9 Total Derivatives Not Subject to a Master Netting Arrangement 260.4 — 260.4 — 260.4 Total Derivatives 3,568.2 3,126.7 441.5 12.2 429.3 Securities Purchased under Agreements to Resell (2) $ 62,860.2 $ 62,075.5 $ 784.7 $ 784.7 $ — (1) Derivative assets are reported in Other Assets on the consolidated balance sheets. Other Assets (excluding derivative assets) totaled $10.2 billion and $10.3 billion as of March 31, 2024 and December 31, 2023, respectively. (2) Offsetting of Securities Purchased under Agreements to Resell primarily relates to our involvement in the FICC. (3) Including cash collateral received from counterparties. (4) Including financial assets accepted as collateral which are received from counterparties. (5) Northern Trust did not possess any cash collateral that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2024 and December 31, 2023. The following table provides information regarding the offsetting of derivative liabilities and securities sold under agreements to repurchase within the consolidated balance sheets as of March 31, 2024 and December 31, 2023. TABLE 76: OFFSETTING OF DERIVATIVE LIABILITIES AND SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE MARCH 31, 2024 (In Millions) GROSS RECOGNIZED LIABILITIES GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (3) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET (4) NET AMOUNT (5) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 1,131.3 $ 1,051.2 $ 80.1 $ — $ 80.1 Interest Rate Swaps OTC 477.7 2.7 475.0 — 475.0 Interest Rate Swaps Exchange Cleared 0.2 — 0.2 — 0.2 Other Financial Derivatives 21.0 16.2 4.8 — 4.8 Total Derivatives Subject to a Master Netting Arrangement 1,630.2 1,070.1 560.1 — 560.1 Total Derivatives Not Subject to a Master Netting Arrangement 186.8 — 186.8 — 186.8 Total Derivatives 1,817.0 1,070.1 746.9 — 746.9 Securities Sold under Agreements to Repurchase (2) $ 66,375.9 $ 65,864.5 $ 511.4 $ 511.4 $ — DECEMBER 31, 2023 (In Millions) GROSS RECOGNIZED LIABILITIES GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (3) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET (4) NET AMOUNT (5) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 2,411.7 $ 2,175.7 $ 236.0 $ — $ 236.0 Interest Rate Swaps OTC 368.3 6.0 362.3 — 362.3 Interest Rate Swaps Exchange Cleared 0.9 — 0.9 — 0.9 Other Financial Derivatives 25.4 23.7 1.7 — 1.7 Total Derivatives Subject to a Master Netting Arrangement 2,806.3 2,205.4 600.9 — 600.9 Total Derivatives Not Subject to a Master Netting Arrangement 843.5 — 843.5 — 843.5 Total Derivatives 3,649.8 2,205.4 1,444.4 — 1,444.4 Securities Sold under Agreements to Repurchase (2) $ 62,860.2 $ 62,075.5 $ 784.7 $ 784.7 $ — (1) Derivative liabilities are reported in Other Liabilities on the consolidated balance sheets. Other Liabilities (excluding derivative liabilities) totaled $2.9 billion and $4.0 billion as of March 31, 2024 and December 31, 2023, respectively. (2) Offsetting of Securities Sold under Agreements to Repurchase primarily relates to our involvement in the FICC. (3) Including cash collateral deposited with counterparties. (4) Including financial assets accepted as collateral which are deposited with counterparties. (5) Northern Trust did not place any cash collateral with counterparties that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2024 and December 31, 2023. All of Northern Trust’s securities sold under agreements to repurchase (repurchase agreements) and securities purchased under agreements to resell (reverse repurchase agreements) involve the transfer of financial assets in exchange for cash subject to a right and obligation to repurchase those assets for an agreed upon amount. In the event of a repurchase failure, the cash or financial assets are available for offset. All of Northern Trust’s repurchase agreements and reverse repurchase agreements are subject to a master netting arrangement, which sets forth the rights and obligations for repurchase and offset. Under the master netting arrangement, Northern Trust is entitled to offset receivables from and collateral placed with a single counterparty against obligations owed to that counterparty. In addition, collateral held by Northern Trust can be offset against receivables from that counterparty. Northern Trust has elected to net securities sold under repurchase agreements against those purchased under resale agreements when the GAAP requirements to net are met. Derivative asset and liability positions with a single counterparty can be offset against each other in cases where legally enforceable master netting arrangements or similar agreements exist. Derivative assets and liabilities can be further offset by cash collateral received from, and deposited with, the transacting counterparty. The basis for this view is that, upon termination of transactions subject to a master netting arrangement or similar agreement, the individual derivative receivables do not represent resources to which general creditors have rights and individual derivative payables do not represent claims that are equivalent to the claims of general creditors. Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. Credit risk associated with derivative instruments relates to the failure of the counterparty and the failure of Northern Trust to pay based on the contractual terms of the agreement, and is generally limited to the unrealized fair value gains and losses on these instruments, net of any collateral received or deposited. The amount of credit risk will increase or decrease during the lives of the instruments as interest rates, foreign exchange rates, or equity prices fluctuate. Northern Trust’s risk is controlled by limiting such activity to an approved list of counterparties and by subjecting such activity to the same credit and quality controls as are followed in lending and investment activities. Credit support annexes and other similar agreements are currently in place with a number of Northern Trust’s counterparties which mitigate the aforementioned credit risk associated with derivative activity conducted with those counterparties by requiring that significant net unrealized fair value gains be supported by collateral placed with Northern Trust. Additional cash collateral received from and deposited with derivative counterparties totaling $78.3 million and $60.5 million, respectively, as of March 31, 2024, and $373.1 million and $21.3 million, respectively, as of December 31, 2023, was not offset against derivative assets and liabilities in the consolidated balance sheets as the amounts exceeded the net derivative positions with those counterparties. Certain master netting arrangements Northern Trust enters into with derivative counterparties contain credit-risk-related contingent features in which the counterparty has the option to declare Northern Trust in default and accelerate cash settlement of net derivative liabilities with the counterparty in the event Northern Trust’s credit rating falls below specified levels. The aggregate fair value of all derivative instruments with credit-risk-related contingent features that were in a liability position was $92.7 million and $1.2 billion at March 31, 2024 and December 31, 2023, respectively. Cash collateral amounts deposited with derivative counterparties on those dates included $75.3 million and $1.1 billion, respectively, posted against these liabilities, resulting in a net maximum amount of termination payments that could have been required at March 31, 2024 and December 31, 2023, of $17.4 million and $52.2 million, respectively. Accelerated settlement of these liabilities would not have a material effect on the consolidated financial position or liquidity of Northern Trust.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Pay vs Performance Disclosure
Net Income	$ 214.7	$ 334.6

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Mar. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2024
Accounting Changes and Error Corrections [Abstract]
Basis of Presentation	The consolidated financial statements include the accounts of Northern Trust Corporation (Corporation) and its wholly-owned subsidiary, The Northern Trust Company (Bank), and various other wholly-owned subsidiaries of the Corporation and Bank. Throughout the notes to the consolidated financial statements, the term “Northern Trust” refers to the Corporation and its subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements, as of and for the periods ended March 31, 2024 and 2023, have not been audited by the Corporation’s independent registered public accounting firm. In the opinion of management, all accounting entries and adjustments, including normal recurring accruals, necessary for a fair presentation of the financial position and the results of operations for the interim periods have been made. The accounting and financial reporting policies of Northern Trust conform to U.S. generally accepted accounting principles (GAAP) and reporting practices prescribed for the banking industry.
Recent Accounting Pronouncements	On January 1, 2024, Northern Trust adopted Accounting Standards Update (ASU) No. 2023-02, “Investments—Equity Method and Joint Ventures (Topic 323): Accounting for Investments in Tax Credit Structures Using the Proportional Amortization Method—a consensus of the Emerging Issues Task Force” (ASU 2023-02). The amendments in ASU 2023-02 allow entities to elect the proportional amortization method to account for tax equity investments if certain conditions are met regardless of the tax credit program from which the income tax credits are received. Under the proportional amortization method, an entity amortizes the initial cost of the investment in proportion to the income tax credits and other income tax benefits received and recognizes the net amortization and income tax credits and other income tax benefits in the income statement as a component of income tax expense (benefit). In addition, ASU 2023-02 requires specific disclosures that must be applied to all investments that generate income tax credits and other income tax benefits for which the entity has elected to apply the proportional amortization method in accordance with Subtopic 323-740. Upon adoption of ASU 2023-02, there was no significant impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. Please refer to Note 19—Variable Interest Entities for further information. On January 1, 2024, Northern Trust adopted ASU No. 2022-03, “Fair Value Measurement (Topic 820): Fair Value Measurement of Equity Securities Subject to Contractual Sale Restrictions” (ASU 2022-03). The amendments in ASU 2022-03 clarify that a contractual restriction on the sale of an equity security is not considered part of the unit of account of the equity security and, therefore, is not considered in measuring fair value. ASU 2022-03 also clarifies that an entity cannot, as a separate unit of account, recognize and measure a contractual sale restriction. Additionally, ASU 2022-03 introduces new disclosure requirements to provide investors with information about contractual sale restrictions including the nature and remaining duration of these restrictions. Upon adoption of ASU 2022-03, there was no impact to Northern Trust’s consolidated balance sheets or consolidated statements of income.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurement Inputs and Valuation Techniques	The following table presents the fair values of Northern Trust’s Level 3 liabilities as of March 31, 2024 and December 31, 2023, as well as the valuation techniques, significant unobservable inputs, and quantitative information used to develop significant unobservable inputs for such liabilities as of such dates. TABLE 30: LEVEL 3 SIGNIFICANT UNOBSERVABLE INPUTS MARCH 31, 2024 FINANCIAL INSTRUMENT FAIR VALUE VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES (1) Swaps Related to Sale of Certain Visa Class B Common Shares $21.0 million Discounted Cash Flow Conversion Rate 1.59x 1.59x Visa Class A Appreciation 9.22% 9.22% Expected Duration 6 - 24 months 10 months (1) Weighted average of expected duration based on scenario probability. DECEMBER 31, 2023 FINANCIAL INSTRUMENT FAIR VALUE VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES (1) Swaps Related to Sale of Certain Visa Class B Common Shares $25.4 million Discounted Cash Flow Conversion Rate 1.59x 1.59x Visa Class A Appreciation 10.49% 10.49% Expected Duration 9 - 27 months 13 months (1) Weighted average of expected duration based on scenario probability. The following table presents the fair values of Northern Trust’s Level 3 assets that were measured at fair value on a nonrecurring basis as of March 31, 2024 and December 31, 2023, as well as the valuation technique, significant unobservable inputs and quantitative information used to develop the significant unobservable inputs for such assets as of such dates. TABLE 33: LEVEL 3 NONRECURRING BASIS SIGNIFICANT UNOBSERVABLE INPUTS MARCH 31, 2024 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $0.1 million Market Approach Discount factor applied to real estate collateral-dependent loans to reflect realizable value N/A N/A (1) Includes real estate collateral-dependent loans and other collateral-dependent loans. DECEMBER 31, 2023 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $43.3 million Market Approach Discount factor applied to real estate collateral-dependent loans to reflect realizable value 0.0 % - 20.0% 2.0% (1) Includes real estate collateral-dependent loans and other collateral-dependent loans.
Recurring Basis Hierarchy Leveling	The following table presents assets and liabilities measured at fair value on a recurring basis as of March 31, 2024 and December 31, 2023, segregated by fair value hierarchy level. TABLE 31: RECURRING BASIS HIERARCHY LEVELING MARCH 31, 2024 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 6,112.3 $ — $ — $ — $ 6,112.3 Obligations of States and Political Subdivisions — 295.0 — — 295.0 Government Sponsored Agency — 12,351.4 — — 12,351.4 Non-U.S. Government — 307.6 — — 307.6 Corporate Debt — 250.2 — — 250.2 Covered Bonds — 296.8 — — 296.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,860.8 — — 2,860.8 Other Asset-Backed — 2,523.0 — — 2,523.0 Commercial Mortgage-Backed — 641.8 — — 641.8 Total Available for Sale Debt Securities 6,112.3 19,526.6 — — 25,638.9 Other Assets Money Market Investment 95.0 — — — 95.0 Derivative Assets Foreign Exchange Contracts — 1,357.1 — (699.0) 658.1 Interest Rate Contracts — 404.0 — (215.2) 188.8 Total Derivative Assets — 1,761.1 — (914.2) 846.9 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 1,318.1 — (1,051.2) 266.9 Interest Rate Contracts — 477.9 — (2.7) 475.2 Other Financial Derivatives (1) — — 21.0 (16.2) 4.8 Total Derivative Liabilities $ — $ 1,796.0 $ 21.0 $ (1,070.1) $ 746.9 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of March 31, 2024, derivative assets and liabilities shown above also include reductions of $181.0 million and $336.9 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties. DECEMBER 31, 2023 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 3,622.2 $ — $ — $ — $ 3,622.2 Obligations of States and Political Subdivisions — 295.8 — — 295.8 Government Sponsored Agency — 11,553.0 — — 11,553.0 Non-U.S. Government — 264.4 — — 264.4 Corporate Debt — 279.5 — — 279.5 Covered Bonds — 347.1 — — 347.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,899.9 — — 2,899.9 Other Asset-Backed — 2,962.6 — — 2,962.6 Commercial Mortgage-Backed — 865.3 — — 865.3 Total Available for Sale 3,622.2 19,467.6 — — 23,089.8 Trading Account — — — — — Total Available for Sale Debt Securities 3,622.2 19,467.6 — — 23,089.8 Other Assets Money Market Investment 95.0 — — — 95.0 Derivative Assets Foreign Exchange Contracts — 3,266.7 — (2,937.2) 329.5 Interest Rate Contracts — 301.5 — (189.5) 112.0 Total Derivative Assets — 3,568.2 — (3,126.7) 441.5 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 3,255.2 — (2,175.7) 1,079.5 Interest Rate Contracts — 369.2 — (6.0) 363.2 Other Financial Derivatives (1) — — 25.4 (23.7) 1.7 Total Derivative Liabilities $ — $ 3,624.4 $ 25.4 $ (2,205.4) $ 1,444.4 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of December 31, 2023, derivative assets and liabilities shown above also include reductions of $2,093.8 million and $1,172.5 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1)
Changes in Level 3 Liabilities	The following table presents the changes in Level 3 liabilities for the three months ended March 31, 2024 and 2023. TABLE 32: CHANGES IN LEVEL 3 LIABILITIES (In Millions) SWAPS RELATED TO SALE OF CERTAIN VISA CLASS B COMMON SHARES THREE MONTHS ENDED MARCH 31, 2024 2023 Fair Value at January 1 $ 25.4 $ 34.8 Total (Gains) Losses: Included in Earnings (1) 1.2 7.6 Purchases, Issues, Sales, and Settlements Settlements (5.5) (7.8) Fair Value at March 31 $ 21.1 $ 34.6 (1) (Gains) losses are recorded in Other Operating Income on the consolidated statements of income.
Fair Value of Financial Instruments	The following tables present the book value and estimated fair value, including the fair value hierarchy level, of Northern Trust’s financial instruments that are not measured at fair value on the consolidated balance sheets as of March 31, 2024 and December 31, 2023. The following tables exclude those items measured at fair value on a recurring basis. TABLE 34: FAIR VALUE OF FINANCIAL INSTRUMENTS MARCH 31, 2024 ESTIMATED FAIR VALUE (In Millions) BOOK VALUE TOTAL ESTIMATED FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 FINANCIAL ASSETS Cash and Due from Banks $ 5,308.7 $ 5,308.7 $ 5,308.7 $ — $ — Federal Reserve and Other Central Bank Deposits 40,269.9 40,269.9 — 40,269.9 — Interest-Bearing Deposits with Banks 1,372.1 1,372.1 — 1,372.1 — Securities Purchased under Agreements to Resell 500.1 500.1 — 500.1 — Debt Securities - Held to Maturity 23,497.9 21,641.4 — 21,641.4 — Loans Held for Investment 47,180.1 47,179.4 — — 47,179.4 Other Assets 1,505.7 1,490.3 95.2 1,395.1 — FINANCIAL LIABILITIES Deposits 123,941.7 123,996.6 — 123,996.6 — Federal Funds Purchased 2,600.5 2,600.5 — 2,600.5 — Securities Sold Under Agreements to Repurchase 511.4 511.4 — 511.4 — Other Borrowings 6,526.2 6,544.3 — 6,544.3 — Senior Notes 2,743.5 2,771.3 — 2,771.3 — Long-Term Debt 4,069.0 4,135.7 — 4,135.7 — Unfunded Commitments 163.3 163.3 — 163.3 — Other Liabilities 42.7 42.7 — — 42.7 DECEMBER 31, 2023 ESTIMATED FAIR VALUE (In Millions) BOOK VALUE TOTAL ESTIMATED FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 FINANCIAL ASSETS Cash and Due from Banks $ 4,791.5 $ 4,791.5 $ 4,791.5 $ — $ — Federal Reserve and Other Central Bank Deposits 34,326.2 34,326.2 — 34,326.2 — Interest-Bearing Deposits with Banks 1,939.0 1,939.0 — 1,939.0 — Securities Purchased under Agreements to Resell 784.7 784.7 — 784.7 — Debt Securities - Held to Maturity 26,221.7 24,473.0 — 24,473.0 — Loans Held for Investment 47,438.3 47,598.3 — — 47,598.3 Other Assets 1,476.6 1,458.0 86.1 1,371.9 — FINANCIAL LIABILITIES Deposits 116,164.0 116,207.6 — 116,207.6 — Federal Funds Purchased 3,045.4 3,045.4 — 3,045.4 — Securities Sold Under Agreements to Repurchase 784.7 784.7 — 784.7 — Other Borrowings 6,567.8 6,607.4 — 6,607.4 — Senior Notes 2,773.2 2,798.1 — 2,798.1 — Long-Term Debt 4,065.0 4,186.8 — 4,186.8 — Unfunded Commitments 178.8 178.8 — 178.8 — Other Liabilities 74.9 74.9 — — 74.9

Securities (Tables)

Securities (Tables)	3 Months Ended
	Mar. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Reconciliation of Amortized Cost to Fair Value of Securities Available for Sale	The following tables provide the amortized cost and fair values as of March 31, 2024 and December 31, 2023, and remaining maturities of AFS debt securities as of March 31, 2024. TABLE 35: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF AVAILABLE FOR SALE DEBT SECURITIES MARCH 31, 2024 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 6,121.6 $ 11.0 $ 20.3 $ 6,112.3 Obligations of States and Political Subdivisions 309.6 — 14.6 295.0 Government Sponsored Agency 12,501.9 12.5 163.0 12,351.4 Non-U.S. Government 325.0 0.1 17.5 307.6 Corporate Debt 256.5 0.2 6.5 250.2 Covered Bonds 302.7 0.3 6.2 296.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,912.6 3.8 55.6 2,860.8 Other Asset-Backed 2,552.4 1.6 31.0 2,523.0 Commercial Mortgage-Backed 659.6 0.2 18.0 641.8 Total $ 25,941.9 $ 29.7 $ 332.7 $ 25,638.9 DECEMBER 31, 2023 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 3,681.5 $ 2.2 $ 61.5 $ 3,622.2 Obligations of States and Political Subdivisions 315.8 — 20.0 295.8 Government Sponsored Agency 11,744.3 9.0 200.3 11,553.0 Non-U.S. Government 284.8 — 20.4 264.4 Corporate Debt 287.5 0.1 8.1 279.5 Covered Bonds 356.8 — 9.7 347.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,013.8 0.1 114.0 2,899.9 Other Asset-Backed 3,061.0 1.6 100.0 2,962.6 Commercial Mortgage-Backed 913.5 0.2 48.4 865.3 Total $ 23,659.0 $ 13.2 $ 582.4 $ 23,089.8
Remaining Maturity of Securities Available for Sale and Held to Maturity	TABLE 36: REMAINING MATURITY OF AVAILABLE FOR SALE DEBT SECURITIES MARCH 31, 2024 ONE YEAR OR LESS ONE TO FIVE YEARS FIVE TO TEN YEARS OVER TEN YEARS TOTAL (In Millions) AMORTIZED COST FAIR VALUE AMORTIZED COST FAIR VALUE AMORTIZED COST FAIR VALUE AMORTIZED COST FAIR VALUE AMORTIZED COST FAIR VALUE U.S. Government $ 348.1 $ 344.2 $ 3,422.0 $ 3,412.9 $ 2,351.5 $ 2,355.2 $ — $ — $ 6,121.6 $ 6,112.3 Obligations of States and Political Subdivisions — — 111.2 106.5 198.4 188.5 — — 309.6 295.0 Government Sponsored Agency 2,631.6 2,606.9 5,460.5 5,396.1 3,409.8 3,375.2 1,000.0 973.2 12,501.9 12,351.4 Non-U.S. Government 64.8 63.5 260.2 244.1 — — — — 325.0 307.6 Corporate Debt 103.1 102.3 153.4 147.9 — — — — 256.5 250.2 Covered Bonds 66.4 65.9 236.3 230.9 — — — — 302.7 296.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 126.8 125.4 2,564.7 2,525.9 221.1 209.5 — — 2,912.6 2,860.8 Other Asset-Backed 218.3 213.5 2,108.8 2,083.8 122.7 123.0 102.6 102.7 2,552.4 2,523.0 Commercial Mortgage-Backed 21.7 20.6 577.1 570.2 60.8 51.0 — — 659.6 641.8 Total $ 3,580.8 $ 3,542.3 $ 14,894.2 $ 14,718.3 $ 6,364.3 $ 6,302.4 $ 1,102.6 $ 1,075.9 $ 25,941.9 $ 25,638.9 Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments. TABLE 39: REMAINING MATURITY OF HELD TO MATURITY DEBT SECURITIES MARCH 31, 2024 ONE YEAR OR LESS ONE TO FIVE YEARS FIVE TO TEN YEARS OVER TEN YEARS TOTAL (In Millions) Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Amortized Cost Fair Value Obligations of States and Political Subdivisions $ 60.4 $ 60.0 $ 1,206.8 $ 1,174.1 $ 1,039.9 $ 998.1 $ 264.5 $ 250.2 $ 2,571.6 $ 2,482.4 Government Sponsored Agency 990.3 883.6 3,419.8 3,038.5 3,138.9 2,768.6 1,674.3 1,435.0 9,223.3 8,125.7 Non-U.S. Government 1,569.9 1,564.7 1,139.3 1,056.5 32.9 28.7 — — 2,742.1 2,649.9 Corporate Debt 247.8 243.0 347.3 329.8 15.2 12.8 — — 610.3 585.6 Covered Bonds 493.8 492.7 1,389.9 1,310.4 226.6 204.1 — — 2,110.3 2,007.2 Certificates of Deposit 403.2 403.0 — — — — — — 403.2 403.0 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 1,058.4 1,035.1 3,960.5 3,697.1 5.6 4.5 — — 5,024.5 4,736.7 Other Asset-Backed 1.2 1.2 120.7 121.5 71.8 72.1 — — 193.7 194.8 Commercial Mortgage-Backed — — 37.6 37.3 — — — — 37.6 37.3 Other 50.7 49.2 319.8 285.0 33.1 24.9 177.7 59.7 581.3 418.8 Total $ 4,875.7 $ 4,732.5 $ 11,941.7 $ 11,050.2 $ 4,564.0 $ 4,113.8 $ 2,116.5 $ 1,744.9 $ 23,497.9 $ 21,641.4
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	The following table provides information regarding AFS debt securities with no credit losses reported that had been in a continuous unrealized loss position for less than twelve months and for twelve months or longer as of March 31, 2024 and December 31, 2023. TABLE 37: AVAILABLE FOR SALE DEBT SECURITIES IN UNREALIZED LOSS POSITION WITH NO CREDIT LOSSES REPORTED MARCH 31, 2024 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ 87.4 $ 12.0 $ 819.5 $ 8.3 $ 906.9 $ 20.3 Obligations of States and Political Subdivisions 295.0 14.6 — — 295.0 14.6 Government Sponsored Agency 145.3 7.9 8,865.2 155.1 9,010.5 163.0 Non-U.S. Government 63.5 1.3 189.5 16.2 253.0 17.5 Corporate Debt 36.9 0.9 55.7 0.9 92.6 1.8 Covered Bonds 60.4 0.5 104.9 5.7 165.3 6.2 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 110.0 5.0 1,066.0 50.6 1,176.0 55.6 Other Asset-Backed 13.9 0.7 995.0 30.3 1,008.9 31.0 Commercial Mortgage-Backed 6.0 0.4 607.4 17.6 613.4 18.0 Total $ 818.4 $ 43.3 $ 12,703.2 $ 284.7 $ 13,521.6 $ 328.0 Note: Two corporate debt AFS securities with a fair value of $80.1 million and unrealized losses of $4.7 million have been excluded from the table above as these AFS securities have a $0.5 million allowance for credit losses reported as of March 31, 2024. Refer to the discussion further below and Note 6—Allowance for Credit Losses for further information. DECEMBER 31, 2023 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ — $ — $ 3,364.7 $ 61.5 $ 3,364.7 $ 61.5 Obligations of States and Political Subdivisions 87.8 5.9 208.0 14.1 295.8 20.0 Government Sponsored Agency 331.0 11.5 9,486.6 188.8 9,817.6 200.3 Non-U.S. Government — — 264.5 20.4 264.5 20.4 Corporate Debt 4.4 0.1 143.0 2.1 147.4 2.2 Covered Bonds — — 213.2 9.7 213.2 9.7 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — — 2,477.0 105.8 2,477.0 105.8 Other Asset-Backed 19.8 2.0 1,998.7 98.0 2,018.5 100.0 Commercial Mortgage-Backed 60.0 4.6 776.6 43.8 836.6 48.4 Total $ 503.0 $ 24.1 $ 18,932.3 $ 544.2 $ 19,435.3 $ 568.3 Note: Three corporate debt AFS securities with a fair value of $98.4 million and unrealized losses of $5.9 million and one sub-sovereign, supranational and non-U.S. agency bonds AFS security with a fair value of $71.0 million and unrealized loss of $8.2 million have been excluded from the table above as these AFS securities have a $1.2 million allowance for credit losses reported as of December 31, 2023. Refer to the discussion further below and Note 6—Allowance for Credit Losses for further information.
Debt Securities, Held-to-maturity	The following tables provide the amortized cost and fair values as of March 31, 2024 and December 31, 2023, and remaining maturities of HTM debt securities as of March 31, 2024. TABLE 38: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF HELD TO MATURITY DEBT SECURITIES MARCH 31, 2024 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR Obligations of States and Political Subdivisions $ 2,571.6 $ 0.3 $ 89.5 $ 2,482.4 Government Sponsored Agency 9,223.3 1.6 1,099.2 8,125.7 Non-U.S. Government 2,742.1 0.1 92.3 2,649.9 Corporate Debt 610.3 — 24.7 585.6 Covered Bonds 2,110.3 0.7 103.8 2,007.2 Certificates of Deposit 403.2 — 0.2 403.0 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 5,024.5 1.6 289.4 4,736.7 Other Asset-Backed 193.7 1.3 0.2 194.8 Commercial Mortgage-Backed 37.6 — 0.3 37.3 Other 581.3 — 162.5 418.8 Total $ 23,497.9 $ 5.6 $ 1,862.1 $ 21,641.4 DECEMBER 31, 2023 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR Obligations of States and Political Subdivisions 2,563.9 0.5 72.4 2,492.0 Government Sponsored Agency 9,355.3 2.3 1,012.4 8,345.2 Non-U.S. Government 4,789.1 0.2 90.7 4,698.6 Corporate Debt 646.1 — 28.2 617.9 Covered Bonds 2,208.6 0.3 108.3 2,100.6 Certificates of Deposit 585.1 — 0.7 584.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 5,245.5 3.2 294.9 4,953.8 Other Asset-Backed 214.2 0.4 0.2 214.4 Commercial Mortgage-Backed 37.6 — 0.8 36.8 Other 576.3 — 147.0 429.3 Total $ 26,221.7 $ 6.9 $ 1,755.6 $ 24,473.0
Debt Securities, Held-to-maturity, Credit Quality Indicator	The following table provides the amortized cost of HTM debt securities by credit rating. TABLE 40: AMORTIZED COST OF HELD TO MATURITY DEBT SECURITIES BY CREDIT RATING MARCH 31, 2024 ($ In Millions) AAA AA A BBB NOT RATED TOTAL Obligations of States and Political Subdivisions $ 956.9 $ 1,614.7 $ — $ — $ — $ 2,571.6 Government Sponsored Agency 9,223.3 — — — — 9,223.3 Non-U.S. Government 896.7 707.4 812.9 325.1 — 2,742.1 Corporate Debt 2.2 298.7 309.4 — — 610.3 Covered Bonds 2,110.3 — — — — 2,110.3 Certificates of Deposit 355.4 — — — 47.8 403.2 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,840.8 1,153.1 29.5 1.1 — 5,024.5 Other Asset-Backed 193.7 — — — — 193.7 Commercial Mortgage-Backed 37.6 — — — — 37.6 Other 52.5 — — — 528.8 581.3 Total $ 17,669.4 $ 3,773.9 $ 1,151.8 $ 326.2 $ 576.6 $ 23,497.9 Percent of Total 75 % 16 % 5 % 1 % 3 % 100 % DECEMBER 31, 2023 ($ In Millions) AAA AA A BBB NOT RATED TOTAL U.S. Government $ — $ — $ — $ — $ — $ — Obligations of States and Political Subdivisions 954.7 1,609.0 — — 0.2 2,563.9 Government Sponsored Agency 9,355.3 — — — — 9,355.3 Non-U.S. Government 813.3 1,179.6 2,463.3 332.9 — 4,789.1 Corporate Debt 2.1 302.6 341.4 — — 646.1 Covered Bonds 2,208.6 — — — — 2,208.6 Certificates of Deposit 545.9 — — — 39.2 585.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 4,047.9 1,166.5 30.0 1.1 — 5,245.5 Other Asset-Backed 214.2 — — — — 214.2 Commercial Mortgage-Backed 37.6 — — — — 37.6 Other 54.8 — — — 521.5 576.3 Total $ 18,234.4 $ 4,257.7 $ 2,834.7 $ 334.0 $ 560.9 $ 26,221.7 Percent of Total 70 % 16 % 11 % 1 % 2 % 100 %

Loans (Tables)

Loans (Tables)	3 Months Ended
	Mar. 31, 2024
Receivables [Abstract]
Loans	Amounts outstanding for Loans, by segment and class, are shown in the following table. TABLE 41: LOANS (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Commercial Commercial and Institutional (1) $ 10,980.6 $ 11,555.3 Commercial Real Estate 5,333.0 5,134.2 Non-U.S. (1) 2,372.7 2,778.5 Other 6,730.8 5,944.8 Total Commercial 25,417.1 25,412.8 Personal Private Client 14,092.2 14,360.0 Residential Real Estate 6,315.2 6,327.1 Non-U.S. 387.2 428.8 Other 1,130.9 1,088.3 Total Personal 21,925.5 22,204.2 Total Loans $ 47,342.6 $ 47,617.0 (1)
Borrower Ratings	Loan segment and class balances as of March 31, 2024 and December 31, 2023 are provided in the following table, segregated by borrower ratings into “1 to 3,” “4 to 5” and “6 to 9” (watch list and nonaccrual status) categories by year of origination at amortized cost basis. Loans that are held for investment are reported at the principal amount outstanding, net of unearned income. TABLE 42: CREDIT QUALITY INDICATOR AT AMORTIZED COST BASIS BY ORIGINATION YEAR March 31, 2024 TERM LOANS REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2024 2023 2022 2021 2020 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 40.2 $ 411.4 $ 458.1 $ 715.7 $ 69.9 $ 539.6 $ 4,735.9 $ 15.0 $ 6,985.8 4 to 5 Category 51.1 757.9 757.4 627.1 117.6 218.3 1,196.2 78.6 3,804.2 6 to 9 Category — 4.2 75.5 57.6 3.9 1.7 45.9 1.8 190.6 Total Commercial and Institutional 91.3 1,173.5 1,291.0 1,400.4 191.4 759.6 5,978.0 95.4 10,980.6 C&I Gross Charge-offs — (7.3) (1.3) — — — — — (8.6) Commercial Real Estate Risk Rating: 1 to 3 Category 9.3 346.9 411.7 277.7 25.7 78.6 67.0 — 1,216.9 4 to 5 Category 151.9 1,617.5 1,087.7 392.9 208.6 340.6 204.5 7.8 4,011.5 6 to 9 Category — 16.1 35.3 30.3 2.5 20.4 — — 104.6 Total Commercial Real Estate 161.2 1,980.5 1,534.7 700.9 236.8 439.6 271.5 7.8 5,333.0 Commercial Real Estate Gross Charge-offs — — (2.4) — — — — — (2.4) Non-U.S. Risk Rating: 1 to 3 Category 950.4 — — 43.0 44.7 22.3 933.5 — 1,993.9 4 to 5 Category 176.9 26.9 0.8 — — 100.7 58.2 — 363.5 6 to 9 Category 1.1 — 14.2 — — — — — 15.3 Total Non-U.S. 1,128.4 26.9 15.0 43.0 44.7 123.0 991.7 — 2,372.7 Other Risk Rating: 1 to 3 Category 3,865.8 — — — — — — — 3,865.8 4 to 5 Category 2,865.0 — — — — — — — 2,865.0 Total Other 6,730.8 — — — — — — — 6,730.8 Other Gross Charge-offs — — — — — — — — — Total Commercial 8,111.7 3,180.9 2,840.7 2,144.3 472.9 1,322.2 7,241.2 103.2 25,417.1 Commercial Gross Charge-offs — (7.3) (3.7) — — — — — (11.0) Personal Private Client Risk Rating: 1 to 3 Category 28.9 472.7 109.5 49.5 60.1 96.0 5,056.1 168.2 6,041.0 4 to 5 Category 21.8 324.3 449.6 519.5 96.3 190.3 5,970.2 451.9 8,023.9 6 to 9 Category — 16.2 0.2 — — — 10.9 — 27.3 Total Private Client 50.7 813.2 559.3 569.0 156.4 286.3 11,037.2 620.1 14,092.2 Residential Real Estate Risk Rating: 1 to 3 Category 42.8 272.2 409.4 430.1 367.5 863.2 230.9 — 2,616.1 4 to 5 Category 44.3 203.3 738.1 766.8 675.2 1,042.9 161.7 — 3,632.3 6 to 9 Category — — 7.3 0.1 0.4 45.6 13.4 — 66.8 Total Residential Real Estate 87.1 475.5 1,154.8 1,197.0 1,043.1 1,951.7 406.0 — 6,315.2 Residential Real Estate Gross Charge-offs — — — — — (0.1) — — (0.1) Non-U.S. Risk Rating: 1 to 3 Category 0.4 3.8 — 0.6 — 4.5 43.9 — 53.2 4 to 5 Category — 23.9 15.5 23.3 — 24.9 231.0 7.4 326.0 6 to 9 Category 8.0 — — — — — — — 8.0 Total Non-U.S. 8.4 27.7 15.5 23.9 — 29.4 274.9 7.4 387.2 Other Risk Rating: 1 to 3 Category 636.3 — — — — — — — 636.3 4 to 5 Category 494.6 — — — — — — — 494.6 Total Other 1,130.9 — — — — — — — 1,130.9 Total Personal 1,277.1 1,316.4 1,729.6 1,789.9 1,199.5 2,267.4 11,718.1 627.5 21,925.5 Personal Gross Charge-offs — — — — — (0.1) — — (0.1) Total Loans $ 9,388.8 $ 4,497.3 $ 4,570.3 $ 3,934.2 $ 1,672.4 $ 3,589.6 $ 18,959.3 $ 730.7 $ 47,342.6 Total Loans Gross Charge-offs (1) $ — $ (7.3) $ (3.7) $ — $ — $ (0.1) $ — $ — $ (11.1) (1) There was $4 million of charge-offs for the three months ended March 31, 2023. December 31, 2023 TERM LOANS REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2023 2022 2021 2020 2019 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 443.9 $ 534.1 $ 668.3 $ 78.1 $ 137.2 $ 409.9 $ 4,909.8 $ 15.0 $ 7,196.3 4 to 5 Category 801.4 790.9 729.5 138.7 120.5 178.7 1,332.4 72.0 4,164.1 6 to 9 Category 13.8 70.0 60.8 12.0 0.1 1.7 34.7 1.8 194.9 Total Commercial and Institutional 1,259.1 1,395.0 1,458.6 228.8 257.8 590.3 6,276.9 88.8 11,555.3 Commercial Real Estate Risk Rating: 1 to 3 Category 403.6 389.9 159.1 23.9 37.8 44.8 51.0 — 1,110.1 4 to 5 Category 1,513.5 1,208.8 521.0 218.4 252.8 96.0 136.3 7.9 3,954.7 6 to 9 Category 16.1 — 30.5 — 8.2 14.6 — — 69.4 Total Commercial Real Estate 1,933.2 1,598.7 710.6 242.3 298.8 155.4 187.3 7.9 5,134.2 CRE Gross Charge-offs (0.7) (4.4) — — — — — — (5.1) Non-U.S. Risk Rating: 1 to 3 Category 487.9 — 43.2 65.2 34.2 3.3 760.0 — 1,393.8 4 to 5 Category 974.7 0.8 — — — 150.0 243.4 — 1,368.9 6 to 9 Category 1.5 14.3 — — — — — — 15.8 Total Non-U.S. 1,464.1 15.1 43.2 65.2 34.2 153.3 1,003.4 — 2,778.5 Other Risk Rating: 1 to 3 Category 4,313.2 — — — — — — — 4,313.2 4 to 5 Category 1,631.6 — — — — — — — 1,631.6 Total Other 5,944.8 — — — — — — — 5,944.8 Other Gross Charge-offs (0.6) — — — — — — — (0.6) Total Commercial 10,601.2 3,008.8 2,212.4 536.3 590.8 899.0 7,467.6 96.7 25,412.8 Commercial Gross Charge-offs (1.3) (4.4) — — — — — — (5.7) Personal Private Client Risk Rating: 1 to 3 Category 504.7 140.8 52.3 67.5 8.7 134.7 5,320.9 168.1 6,397.7 4 to 5 Category 290.1 488.2 655.1 100.9 158.8 44.7 5,721.5 447.8 7,907.1 6 to 9 Category 23.6 0.3 — — — 18.3 13.0 — 55.2 Total Private Client 818.4 629.3 707.4 168.4 167.5 197.7 11,055.4 615.9 14,360.0 Residential Real Estate Risk Rating: 1 to 3 Category 278.7 464.0 500.6 373.3 142.4 722.4 219.8 — 2,701.2 4 to 5 Category 191.6 694.9 717.4 686.7 290.0 805.3 170.3 — 3,556.2 6 to 9 Category — 10.9 — 0.7 1.6 43.6 12.9 — 69.7 Total Residential Real Estate 470.3 1,169.8 1,218.0 1,060.7 434.0 1,571.3 403.0 — 6,327.1 RRE Gross Charge-offs (0.8) — — — — (1.0) — — (1.8) Non-U.S. Risk Rating: 1 to 3 Category 15.5 — 0.6 — — 4.6 71.4 — 92.1 4 to 5 Category 12.7 16.0 39.2 — 16.4 8.9 236.1 7.4 336.7 6 to 9 Category — — — — — — — — — Total Non-U.S. 28.2 16.0 39.8 — 16.4 13.5 307.5 7.4 428.8 Other Risk Rating: 1 to 3 Category 461.7 — — — — — — — 461.7 4 to 5 Category 626.6 — — — — — — — 626.6 Total Other 1,088.3 — — — — — — — 1,088.3 Total Personal 2,405.2 1,815.1 1,965.2 1,229.1 617.9 1,782.5 11,765.9 623.3 22,204.2 Personal Gross Charge-Offs $ (0.8) $ — $ — $ — $ — $ (1.0) $ — $ — $ (1.8) Total Loans 13,006.4 4,823.9 4,177.6 1,765.4 1,208.7 2,681.5 19,233.5 720.0 47,617.0 Total Loans Gross Charge-Offs $ (2.1) $ (4.4) $ — $ — $ — $ (1.0) $ — $ — $ (7.5)
Delinquency Status	The following table provides balances and delinquency status of accrual and nonaccrual loans by segment and class, as well as the other real estate owned and nonaccrual asset balances, as of March 31, 2024 and December 31, 2023. TABLE 43: DELINQUENCY STATUS ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS March 31, 2024 Commercial Commercial and Institutional $ 10,963.0 $ 7.3 $ — $ 2.7 $ 10,973.0 $ 7.6 $ 10,980.6 $ 7.6 Commercial Real Estate 5,265.2 56.0 — 6.1 5,327.3 5.7 5,333.0 5.7 Non-U.S. 2,372.7 — — — 2,372.7 — 2,372.7 — Other 6,730.8 — — — 6,730.8 — 6,730.8 — Total Commercial 25,331.7 63.3 — 8.8 25,403.8 13.3 25,417.1 13.3 Personal Private Client 13,941.1 112.6 18.5 18.0 14,090.2 2.0 14,092.2 — Residential Real Estate 6,261.2 18.5 10.8 3.0 6,293.5 21.7 6,315.2 21.7 Non-U.S. 354.8 32.4 — — 387.2 — 387.2 — Other 1,130.9 — — — 1,130.9 — 1,130.9 — Total Personal 21,688.0 163.5 29.3 21.0 21,901.8 23.7 21,925.5 21.7 Total Loans $ 47,019.7 $ 226.8 $ 29.3 $ 29.8 $ 47,305.6 $ 37.0 $ 47,342.6 $ 35.0 Other Real Estate Owned $ — Total Nonaccrual Assets $ 37.0 ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS December 31, 2023 Commercial Commercial and Institutional $ 11,374.6 $ 163.7 $ 0.7 $ — $ 11,539.0 $ 16.3 $ 11,555.3 $ 4.1 Commercial Real Estate 5,123.7 4.4 6.1 — 5,134.2 — 5,134.2 — Non-U.S. 2,778.5 — — — 2,778.5 — 2,778.5 — Other 5,944.8 — — — 5,944.8 — 5,944.8 — Total Commercial 25,221.6 168.1 6.8 — 25,396.5 16.3 25,412.8 4.1 Personal Private Client 14,240.0 63.9 24.8 11.0 14,339.7 20.3 14,360.0 18.3 Residential Real Estate 6,283.0 7.5 0.5 9.1 6,300.1 27.0 6,327.1 27.0 Non-U.S 428.2 — 0.6 — 428.8 — 428.8 — Other 1,088.3 — — — 1,088.3 — 1,088.3 — Total Personal 22,039.5 71.4 25.9 20.1 22,156.9 47.3 22,204.2 45.3 Total Loans $ 47,261.1 $ 239.5 $ 32.7 $ 20.1 $ 47,553.4 $ 63.6 $ 47,617.0 $ 49.4 Other Real Estate Owned $ 1.5 Total Nonaccrual Assets $ 65.1
Financing Receivable, Troubled Debt Restructuring	The following table shows the amortized cost basis of loan modifications provided to financially distressed borrowers that impacted the respective cash flows of the underlying loans as of March 31, 2024 and March 31, 2023, disaggregated by relevant class of financing receivable and type of modification provided. TABLE 44: LOAN MODIFICATIONS MADE TO BORROWERS EXPERIENCING FINANCIAL DIFFICULTY THREE MONTHS ENDED MARCH 31, 2024 THREE MONTHS ENDED MARCH 31, 2023 ($ In Millions) LOAN MODIFICATION DETAIL AMORTIZED COST BASIS % OF TOTAL SEGMENT AMORTIZED COST BASIS % OF TOTAL SEGMENT Commercial Total Commercial $ — — % $ — — % Personal Residential Real Estate Deferred Principal and Interest $ — — % $ 2.9 0.05 % Residential Real Estate Extension of Term 0.1 — — — Private Client Extension of Term 0.2 — — — Total Personal $ 0.3 — % $ 2.9 0.05 % Total Loans $ 0.3 — % $ 2.9 0.05 % The following table describes the financial effect of the modifications made to borrowers experiencing financial difficulty. TABLE 45: FINANCIAL EFFECT OF MODIFICATIONS MADE TO BORROWERS EXPERIENCING FINANCIAL DIFFICULTY THREE MONTHS ENDED MARCH 31, 2024 THREE MONTHS ENDED MARCH 31, 2023 FINANCIAL EFFECT FINANCIAL EFFECT PRINCIPAL AND INTEREST DEFERRAL Personal Residential Real Estate — Northern Trust provided a weighted average of 180 days payment deferrals to borrowers for immaterial principal and interest deferral amounts. These payments are, in general, due at the end of the deferral period. TERM EXTENSION Personal Residential Real Estate Northern Trust provided weighted average term extensions of 14 months. — Private Client Northern Trust provided weighted average term extensions of 22 months. —

Allowance for Credit Losses (Ta

Allowance for Credit Losses (Tables)	3 Months Ended
	Mar. 31, 2024
Receivables [Abstract]
Allowance for Credit Loss	The following table provides information regarding changes in the total allowance for credit losses during the three months ended March 31, 2024 and 2023. TABLE 46: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES THREE MONTHS ENDED MARCH 31, 2024 (In Millions) LOANS UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT HELD TO MATURITY DEBT SECURITIES OTHER FINANCIAL ASSETS TOTAL Balance at Beginning of Period $ 178.7 $ 26.9 $ 12.7 $ 0.9 $ 219.2 Charge-Offs (11.1) — — — (11.1) Recoveries 0.7 — — — 0.7 Net Recoveries (Charge-Offs) (10.4) — — — (10.4) Provision for Credit Losses (1) (5.9) (1.7) (0.3) 0.1 (7.8) Balance at End of Period $ 162.4 $ 25.2 $ 12.4 $ 1.0 $ 201.0 (1) The table excludes a negative provision for credit losses of $0.7 million for the three months ended March 31, 2024 for AFS debt securities. See further detail in Note 4—Securities. THREE MONTHS ENDED MARCH 31, 2023 (In Millions) LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT HELD TO MATURITY DEBT SECURITIES OTHER FINANCIAL ASSETS TOTAL Balance at Beginning of Period $ 144.3 $ 38.5 $ 16.0 $ 0.8 $ 199.6 Charge-Offs (4.0) — — — (4.0) Recoveries 1.1 — — — 1.1 Net Recoveries (Charge-Offs) (2.9) — — — (2.9) Provision for Credit Losses (1) 18.5 (4.2) — 0.2 14.5 Balance at End of Period $ 159.9 $ 34.3 $ 16.0 $ 1.0 $ 211.2 (1) The table excludes a provision for credit losses of $0.5 million for the three months ended March 31, 2023 for AFS debt securities. See further detail in Note 4—Securities. The following table provides information regarding changes in the total allowance for credit losses related to loans, including undrawn loan commitments and standby letters of credit, by segment during the three months ended March 31, 2024 and 2023. TABLE 47: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO LOANS THREE MONTHS ENDED MARCH 31, 2024 LOANS UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 146.8 $ 31.9 $ 178.7 $ 24.9 $ 2.0 $ 26.9 Charge-Offs (11.0) (0.1) (11.1) — — — Recoveries — 0.7 0.7 — — — Net Recoveries (Charge-Offs) (11.0) 0.6 (10.4) — — — Provision for Credit Losses (4.1) (1.8) (5.9) (2.4) 0.7 (1.7) Balance at End of Period $ 131.7 $ 30.7 $ 162.4 $ 22.5 $ 2.7 $ 25.2 THREE MONTHS ENDED MARCH 31, 2023 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 116.2 $ 28.1 $ 144.3 $ 36.3 $ 2.2 $ 38.5 Charge-Offs (4.0) — (4.0) — — — Recoveries — 1.1 1.1 — — — Net Recoveries (Charge-Offs) (4.0) 1.1 (2.9) — — — Provision for Credit Losses 18.6 (0.1) 18.5 (5.0) 0.8 (4.2) Balance at End of Period $ 130.8 $ 29.1 $ 159.9 $ 31.3 $ 3.0 $ 34.3 The following table provides information regarding the recorded investments in loans and the allowance for credit losses for loans and undrawn loan commitments and standby letters of credit by segment as of March 31, 2024 and December 31, 2023. TABLE 48: RECORDED INVESTMENTS IN LOANS MARCH 31, 2024 DECEMBER 31, 2023 (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Loans Evaluated on an Individual Basis $ 14.5 $ 38.7 $ 53.2 $ 33.7 $ 62.6 $ 96.3 Evaluated on a Collective Basis 25,402.6 21,886.8 47,289.4 25,379.1 22,141.6 47,520.7 Total Loans 25,417.1 21,925.5 47,342.6 25,412.8 22,204.2 47,617.0 Allowance for Credit Losses on Loans Evaluated on an Individual Basis 0.5 2.0 2.5 11.4 2.0 13.4 Evaluated on a Collective Basis 131.2 28.7 159.9 135.4 29.9 165.3 Allowance Assigned to Loans 131.7 30.7 162.4 146.8 31.9 178.7 Allowance for Undrawn Loan Commitments and Standby Letters of Credit Evaluated on a Collective Basis 22.5 2.7 25.2 24.9 2.0 26.9 Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit 22.5 2.7 25.2 24.9 2.0 26.9 Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit $ 154.2 $ 33.4 $ 187.6 $ 171.7 $ 33.9 $ 205.6
Debt Securities, Held-to-maturity, Allowance for Credit Loss	The following table provides information regarding changes in the total allowance for credit losses for HTM debt securities during the three months ended March 31, 2024 and 2023. TABLE 49: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO HELD TO MATURITY DEBT SECURITIES THREE MONTHS ENDED MARCH 31, 2024 (In Millions) CORPORATE DEBT NON-U.S. GOVERNMENT SUB-SOVEREIGN, SUPRANATIONAL, AND NON-U.S. AGENCY BONDS OBLIGATIONS OF STATES AND POLITICAL SUBDIVISIONS (1) COVERED BONDS OTHER TOTAL Balance at Beginning of Period $ 0.9 $ 3.5 $ 2.2 $ 1.2 $ 0.1 $ 4.8 $ 12.7 Provision for Credit Losses (0.1) — (0.1) (0.1) — — (0.3) Balance at End of Period $ 0.8 $ 3.5 $ 2.1 $ 1.1 $ 0.1 $ 4.8 $ 12.4 (1) The allowance for Obligations of States and Political Subdivisions is related to (non pre-refunded) municipal securities that do not fall under Northern Trust’s zero-loss assumption. THREE MONTHS ENDED MARCH 31, 2023 (In Millions) CORPORATE DEBT NON-U.S. GOVERNMENT SUB-SOVEREIGN, SUPRANATIONAL, AND NON-U.S. AGENCY BONDS OBLIGATIONS OF STATES AND POLITICAL SUBDIVISIONS COVERED BONDS OTHER TOTAL Balance at Beginning of Period $ 1.9 $ 3.6 $ 4.0 $ 1.5 $ 0.1 $ 4.9 $ 16.0 Provision for Credit Losses — 0.3 0.1 (0.2) — (0.2) — Balance at End of Period $ 1.9 $ 3.9 $ 4.1 $ 1.3 $ 0.1 $ 4.7 $ 16.0
Schedule of Accrued Liabilities	The following table provides the amount of accrued interest excluded from the amortized cost basis of the following portfolios. TABLE 50: ACCRUED INTEREST (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Loans $ 253.0 $ 241.7 Debt Securities Held to Maturity 69.8 72.0 Available for Sale 175.0 129.2 Other Financial Assets 110.3 86.0 Total $ 608.1 $ 528.9

Pledged Assets, Collateral an_2

Pledged Assets, Collateral and Restricted Assets (Tables)	3 Months Ended
	Mar. 31, 2024
Transfers and Servicing [Abstract]
Schedule of Financial Instruments Owned and Pledged as Collateral	The following table presents the carrying value of Northern Trust's pledged assets by type. TABLE 51: TYPE OF PLEDGED ASSETS (In Billions) MARCH 31, 2024 DECEMBER 31, 2023 Debt Securities (1) $ 30.8 $ 33.0 Loans (2) 10.6 10.3 Total Pledged Assets $ 41.4 $ 43.3 (1) Debt securities are comprised of held to maturity and available for sale securities. (2) Loans pledged at the FHLB of Chicago and the Federal Reserve Bank of Chicago.
Schedule of Customer Securities for which Entity has Right to Sell or Repledge	The following table presents the fair value of securities accepted as collateral. TABLE 52: ACCEPTED COLLATERAL (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Collateral that may be repledged or sold Reverse repurchase agreements (1)(2) $ 66,327.9 $ 62,767.8 Derivative contracts 3.6 12.2 Collateral that may not be repledged or sold Reverse repurchase agreements — — Total Collateral Accepted $ 66,331.5 $ 62,780.0 (1) The fair value of securities collateral that was repledged or sold totaled $65.7 billion and $62.0 billion at March 31, 2024 and December 31, 2023, respectively. (2) This includes collateral accepted as related to the sponsored member program. Refer to Note 20—Commitments and Contingent Liabilities for further information.

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	3 Months Ended
	Mar. 31, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill by Reporting Segment	Changes by reporting segment in the carrying amount of Goodwill for the three months ended March 31, 2024, including the effect of foreign exchange rates on non-U.S. dollar denominated balances, were as follows. TABLE 53: GOODWILL (In Millions) ASSET WEALTH MANAGEMENT TOTAL Balance at December 31, 2023 $ 621.9 $ 80.4 $ 702.3 Foreign Exchange Rates (4.8) — (4.8) Balance at March 31, 2024 $ 617.1 $ 80.4 $ 697.5
Other Intangible Assets	The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of March 31, 2024 and December 31, 2023 were as follows. TABLE 54: OTHER INTANGIBLE ASSETS (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Gross Carrying Amount $ 130.9 $ 135.0 Less: Accumulated Amortization 63.9 63.4 Net Book Value $ 67.0 $ 71.6 The gross carrying amount and accumulated amortization of capitalized software as of March 31, 2024 and December 31, 2023 were as follows. TABLE 55: CAPITALIZED SOFTWARE (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Gross Carrying Amount $ 3,905.3 $ 3,781.7 Less: Accumulated Amortization 1,893.9 1,754.2 Net Book Value $ 2,011.4 $ 2,027.5

Reporting Segments (Tables)

Reporting Segments (Tables)	3 Months Ended
	Mar. 31, 2024
Segment Reporting [Abstract]
Results of Reporting Segments	The following table presents the earnings contributions and average assets of Northern Trust’s reporting segments for the three-month periods ended March 31, 2024 and 2023. TABLE 56: RESULTS OF REPORTING SEGMENTS ($ In Millions) ASSET SERVICING WEALTH MANAGEMENT OTHER RECONCILING ITEMS TOTAL CONSOLIDATED THREE MONTHS ENDED MARCH 31, 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Noninterest Income Trust, Investment and Other Servicing Fees $ 639.6 $ 603.0 $ 503.3 $ 460.6 $ — $ — $ — $ — $ 1,142.9 $ 1,063.6 Foreign Exchange Trading Income (Loss) 59.9 54.9 (2.9) (1.9) — — — — 57.0 53.0 Other Noninterest Income (Loss) 70.8 63.2 38.5 34.3 (190.5) (0.7) — — (81.2) 96.8 Total Noninterest Income (Loss) 770.3 721.1 538.9 493.0 (190.5) (0.7) — — 1,118.7 1,213.4 Net Interest Income 293.8 312.1 241.6 232.3 — — (7.3) (13.2) 528.1 531.2 Revenue 1,064.1 1,033.2 780.5 725.3 (190.5) (0.7) (7.3) (13.2) 1,646.8 1,744.6 Provision for Credit Losses (5.8) (2.9) (1.7) 17.9 (1.0) — — — (8.5) 15.0 Noninterest Expense 852.7 801.0 491.7 469.2 20.3 15.4 — — 1,364.7 1,285.6 Income before Income Taxes 217.2 235.1 290.5 238.2 (209.8) (16.1) (7.3) (13.2) 290.6 444.0 Provision for Income Taxes 56.6 60.5 81.4 66.1 (54.8) (4.0) (7.3) (13.2) 75.9 109.4 Net Income $ 160.6 $ 174.6 $ 209.1 $ 172.1 $ (155.0) $ (12.1) $ — $ — $ 214.7 $ 334.6 Percentage of Consolidated Net Income N/M 52 % N/M 52 % N/M (4) % N/A N/A 100 % 100 % Average Assets $ 106,955.0 $ 111,215.3 $ 38,163.3 $ 36,844.6 $ — $ — N/A N/A $ 145,118.3 $ 148,059.9 Note: Segment results are stated on an FTE basis. The FTE adjustments are eliminated in the reconciling items column with the Corporation’s total consolidated financial results stated on a GAAP basis. The adjustment to an FTE basis has no impact on Net Income.

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2024
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive Income (Loss)	The following tables summarize the components of Accumulated Other Comprehensive Income (Loss) (AOCI) at March 31, 2024 and 2023, and changes during the three months then ended. TABLE 57: SUMMARY OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED MARCH 31, 2024 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2023 $ (923.9) $ 0.8 $ 203.6 $ (418.4) $ (1,137.9) Net Change 213.4 (0.7) 4.6 3.0 220.3 Balance at March 31, 2024 $ (710.5) $ 0.1 $ 208.2 $ (415.4) $ (917.6) THREE MONTHS ENDED MARCH 31, 2023 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2022 $ (1,367.6) $ 1.2 $ 164.6 $ (367.4) $ (1,569.2) Net Change 180.2 (0.1) 22.7 0.2 203.0 Balance at March 31, 2023 $ (1,187.4) $ 1.1 $ 187.3 $ (367.2) $ (1,366.2)
Details of Changes in Accumulated Other Comprehensive Income (Loss)	TABLE 58: DETAILS OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED MARCH 31, 2024 2023 (In Millions) PRE-TAX TAX AFTER TAX PRE-TAX TAX AFTER TAX Unrealized Gains (Losses) on Available for Sale Debt Securities Unrealized Gains (Losses) on Available for Sale Debt Securities $ 73.2 $ (19.4) $ 53.8 $ 229.3 $ (60.3) $ 169.0 Reclassification Adjustments for (Gains) Losses Included in Net Income: Interest Income on Debt Securities (1) 24.4 (6.2) 18.2 21.9 (5.5) 16.4 Net (Gains) Losses on Debt Securities (2) 189.4 (48.0) 141.4 (6.9) 1.7 (5.2) Net Change $ 287.0 $ (73.6) $ 213.4 $ 244.3 $ (64.1) $ 180.2 Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ 4.5 $ (1.1) $ 3.4 $ 0.5 $ (0.1) $ 0.4 Reclassification Adjustment for (Gains) Losses Included in Net Income (3) (5.5) 1.4 (4.1) (0.6) 0.1 (0.5) Net Change $ (1.0) $ 0.3 $ (0.7) $ (0.1) $ — $ (0.1) Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (58.5) $ 2.9 $ (55.6) $ 46.8 $ 0.2 $ 47.0 Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) (0.6) 0.1 (0.5) — — — Net Investment Hedge Gains (Losses) 81.3 (20.6) 60.7 (32.5) 8.2 (24.3) Net Change $ 22.2 $ (17.6) $ 4.6 $ 14.3 $ 8.4 $ 22.7 Pension and Other Postretirement Benefit Adjustments Net Actuarial Gains (Losses) $ 1.1 $ (0.5) $ 0.6 $ (1.1) $ 0.1 $ (1.0) Reclassification Adjustment for (Gains) Losses Included in Net Income (4) Amortization of Net Actuarial Loss 3.2 (0.8) 2.4 1.6 (0.4) 1.2 Net Change $ 4.3 $ (1.3) $ 3.0 $ 0.5 $ (0.3) $ 0.2 Total Net Change $ 312.5 $ (92.2) $ 220.3 $ 259.0 $ (56.0) $ 203.0 (1) The before-tax reclassification adjustment is related to the unrealized gains (losses) amortization on AFS debt securities that were transferred to HTM debt securities during the second quarter of 2021 and third quarter of 2022. (2) The net gains (losses) on AFS debt securities before-tax reclassification adjustment is recorded in Investment Security Gains (Losses), net on the consolidated statements of income. (3) See Note 21—Derivative Financial Instruments for the location of the reclassification adjustment related to cash flow hedges. (4) The pension and other postretirement benefit before-tax reclassification adjustment is recorded in Employee Benefits expense on the consolidated statements of income.

Net Income Per Common Share (Ta

Net Income Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2024
Earnings Per Share [Abstract]
Net Income per Common Share	The computations of net income per common share are presented in the following table. TABLE 59: NET INCOME PER COMMON SHARE THREE MONTHS ENDED MARCH 31, ($ In Millions Except Per Common Share Information) 2024 2023 Basic Net Income Per Common Share Average Number of Common Shares Outstanding 204,628,796 208,186,841 Net Income $ 214.7 $ 334.6 Less: Dividends on Preferred Stock 16.2 16.2 Net Income Applicable to Common Stock 198.5 318.4 Less: Earnings Allocated to Participating Securities 2.4 3.2 Earnings Allocated to Common Shares Outstanding 196.1 315.2 Basic Net Income Per Common Share $ 0.96 $ 1.51 Diluted Net Income Per Common Share Average Number of Common Shares Outstanding 204,628,796 208,186,841 Plus: Dilutive Effect of Share-based Compensation 506,049 543,548 Average Common and Potential Common Shares 205,134,845 208,730,389 Earnings Allocated to Common and Potential Common Shares $ 196.1 $ 315.2 Diluted Net Income Per Common Share 0.96 1.51

Revenue from Contracts with C_2

Revenue from Contracts with Clients (Tables)	3 Months Ended
	Mar. 31, 2024
Revenue from Contract with Customer [Abstract]
Revenue Disaggregation	The following table presents revenues disaggregated by major revenue source. TABLE 60: REVENUE DISAGGREGATION THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Noninterest Income Trust, Investment and Other Servicing Fees Custody and Fund Administration $ 467.4 $ 441.6 Investment Management and Advisory 593.9 540.5 Securities Lending 18.6 19.1 Other 63.0 62.4 Total Trust, Investment and Other Servicing Fees $ 1,142.9 $ 1,063.6 Other Noninterest Income Foreign Exchange Trading Income $ 57.0 $ 53.0 Treasury Management Fees 9.3 8.4 Security Commissions and Trading Income 37.9 34.7 Other Operating Income 61.0 46.8 Investment Security Gains (Losses), net (189.4) 6.9 Total Other Noninterest Income $ (24.2) $ 149.8 Total Noninterest Income $ 1,118.7 $ 1,213.4
Contract Balances	The table below represents receivables balances from contracts with clients, which are included in Other Assets on the consolidated balance sheets, at March 31, 2024 and December 31, 2023. TABLE 61: CLIENT RECEIVABLES (In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Trust Fees Receivable, net (1) $ 949.4 $ 863.5 Other 47.7 64.9 Total Client Receivables $ 997.1 $ 928.4 (1) Trust Fees Receivable is net of a $14.8 million and $15.9 million fee receivable allowance as of March 31, 2024 and December 31, 2023, respectively.

Net Interest Income (Tables)

Net Interest Income (Tables)	3 Months Ended
	Mar. 31, 2024
Banking and Thrift, Interest [Abstract]
Net Interest Income	The components of Net Interest Income were as follows. TABLE 62: NET INTEREST INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Interest Income Federal Reserve and Other Central Bank Deposits $ 459.7 $ 377.0 Interest-Bearing Due from and Deposits with Banks (1) 34.6 28.2 Federal Funds Sold — 0.2 Securities Purchased under Agreements to Resell 823.9 125.9 Securities — Taxable 445.3 337.8 — Nontaxable (2) 0.3 0.3 Loans 653.6 578.2 Other Interest-Earning Assets (3) 28.2 7.8 Total Interest Income $ 2,445.6 $ 1,455.4 Interest Expense Deposits $ 881.7 $ 564.6 Federal Funds Purchased 33.6 40.1 Securities Sold Under Agreements to Repurchase 813.9 116.1 Other Borrowings 88.6 135.0 Senior Notes 44.1 39.2 Long-Term Debt 55.6 29.2 Total Interest Expense $ 1,917.5 $ 924.2 Net Interest Income $ 528.1 $ 531.2 (1) Interest-Bearing Due from and Deposits with Banks includes the interest-bearing component of Cash and Due from Banks and Interest-Bearing Deposits with Banks as presented on the consolidated balance sheets. (2) Non-taxable Securities represent securities that are exempt from U.S. federal income taxes. (3) Other Interest-Earning Assets include certain community development investments, collateral deposits with certain securities depositories and clearing houses, Federal Home Loan Bank and Federal Reserve stock, and money market investments which are classified in Other Assets on the consolidated balance sheets.

Other Operating Income (Tables)

Other Operating Income (Tables)	3 Months Ended
	Mar. 31, 2024
Other Income and Expenses [Abstract]
Components of Other Operating Income	The components of Other Operating Income were as follows. TABLE 63: OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Loan Service Fees $ 15.7 $ 18.7 Banking Service Fees 13.3 12.2 Bank Owned Life Insurance 20.6 16.7 Other Income (1) 11.4 (0.8) Total Other Operating Income $ 61.0 $ 46.8 (1) Other Income includes the mark-to-market gain or loss on derivative swap activity primarily related to the sale of certain Visa Class B common shares.

Other Operating Expense (Tables

Other Operating Expense (Tables)	3 Months Ended
	Mar. 31, 2024
Other Income and Expenses [Abstract]
Summary of other operating expenses	The components of Other Operating Expense were as follows. TABLE 64: OTHER OPERATING EXPENSE THREE MONTHS ENDED MARCH 31, In Millions) 2024 2023 Business Promotion $ 16.7 $ 16.2 Staff Related 14.2 7.8 FDIC Insurance Premiums (1) 18.7 6.2 Charitable Contributions 2.0 3.2 Other Expenses 48.8 52.2 Total Other Operating Expense $ 100.4 $ 85.6 (1)

Pension (Tables)

Pension (Tables)	3 Months Ended
	Mar. 31, 2024
Retirement Benefits [Abstract]
Net Periodic Pension Expense (Benefit)	The following table sets forth the net periodic pension expense for Northern Trust’s U.S. Qualified Plan, Non-U.S. Pension Plans, and U.S. Non-Qualified Plan for the three months ended March 31, 2024 and 2023. TABLE 65: NET PERIODIC PENSION EXPENSE (BENEFIT) U.S. QUALIFIED PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Service Cost $ 13.4 $ 11.5 Interest Cost 13.9 13.5 Expected Return on Plan Assets (28.9) (25.3) Amortization Net Actuarial Loss 1.9 0.4 Net Periodic Pension Expense $ 0.3 $ 0.1 NON-U.S. PENSION PLANS THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Service Cost $ 0.5 $ 0.3 Interest Cost 1.1 1.2 Expected Return on Plan Assets (1.6) (1.5) Amortization Net Actuarial (Gain) — (0.1) Net Periodic Pension (Benefit) $ — $ (0.1) U.S. NON-QUALIFIED PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Service Cost $ 1.2 $ 1.2 Interest Cost 1.2 1.3 Amortization Net Actuarial Loss 1.3 1.3 Net Periodic Pension Expense $ 3.7 $ 3.8

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2024
Share-Based Payment Arrangement [Abstract]
Total Compensation Expense for Share-Based Payment Arrangements	Total compensation expense for share-based payment arrangements and the associated tax impacts were as follows for the three months ended March 31, 2024 and 2023. TABLE 66: TOTAL COMPENSATION EXPENSE FOR SHARE-BASED PAYMENT ARRANGEMENTS THREE MONTHS ENDED MARCH 31, (In Millions) 2024 2023 Restricted Stock Unit Awards $ 49.4 $ 50.3 Performance Stock Units 17.0 14.1 Total Share-Based Compensation Expense 66.4 64.4 Tax Benefits Recognized $ 16.8 $ 16.2

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	3 Months Ended
	Mar. 31, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Variable Interest Entities	(In Millions) MARCH 31, 2024 DECEMBER 31, 2023 Investment Carrying Amount Affordable Housing $ 603.3 $ 622.8 New Markets 263.1 266.3 Total Investment Carrying Amount (1) $ 866.4 $ 889.1 Unfunded Commitments Affordable Housing $ 163.3 $ 178.8 New Markets — — Total Unfunded Commitments (2) $ 163.3 $ 178.8 (1) As of March 31, 2024 and December 31, 2023, $835.7 million and $857.0 million are VIEs, respectively. (2) As of March 31, 2024 and December 31, 2023, $156.6 million and $172.0 million relate to undrawn commitments on VIEs, respectively.
Schedule of Income Tax Credits and Other Tax Benefits and Amortization Expense	(In Millions) MARCH 31, 2024 MARCH 31, 2023 Income Tax Credits and Other Income Tax Benefits Affordable Housing $ 21.7 $ 22.4 New Markets 5.0 5.9 Total Income Tax Credits and Other Income Tax Benefits $ 26.7 $ 28.3 Amortization Expense Affordable Housing $ 19.5 $ 19.8 New Markets 4.4 4.7 Total Amortization Expense $ 23.9 $ 24.5

Commitments and Contingent Li_2

Commitments and Contingent Liabilities (Tables)	3 Months Ended
	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Schedule of Fair Value, Off-balance Sheet Risks	The following table provides details of Northern Trust's off-balance sheet financial instruments as of March 31, 2024 and December 31, 2023. TABLE 69: SUMMARY OF OFF-BALANCE SHEET FINANCIAL INSTRUMENTS MARCH 31, 2024 DECEMBER 31, 2023 (In Millions) ONE YEAR AND LESS OVER ONE YEAR TOTAL ONE YEAR AND LESS OVER ONE YEAR TOTAL Undrawn Commitments (1) $ 10,322.2 $ 18,957.1 $ 29,279.3 $ 11,849.5 $ 18,909.6 $ 30,759.1 Standby Letters of Credit and Financial Guarantees (2)(3) 90,610.8 327.2 90,938.0 85,752.0 639.0 86,391.0 Commercial Letters of Credit 17.2 0.1 17.3 29.2 1.3 30.5 Securities Lent with Indemnification 138,278.1 — 138,278.1 140,539.1 — 140,539.1 Unsettled Reverse Repurchase Agreements 16,442.4 — 16,442.4 27,667.7 — 27,667.7 Total Off-Balance Sheet Financial Instruments $ 255,670.7 $ 19,284.4 $ 274,955.1 $ 265,837.5 $ 19,549.9 $ 285,387.4 (1) These amounts exclude $259.1 million and $222.2 million of commitments participated to others at March 31, 2024 and December 31, 2023, respectively. (2) These amounts include $41.0 million and $39.1 million of standby letters of credit secured by cash deposits or participated to others as of March 31, 2024 and December 31, 2023, respectively. (3) These amounts include a $89.3 billion and $84.6 billion guarantee to the Fixed Income Clearing Corporation (FICC) under the sponsored member program, without taking into consideration the related collateral, as of March 31, 2024 and December 31, 2023, respectively. Northern Trust became a sponsored member during the third quarter of 2021.

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Notional and Fair Value Amounts of Client-related and Trading Derivative Financial Instruments	The following table shows the notional and fair values of all derivative financial instruments as of March 31, 2024 and December 31, 2023. TABLE 70: NOTIONAL AND FAIR VALUES OF DERIVATIVE FINANCIAL INSTRUMENTS MARCH 31, 2024 DECEMBER 31, 2023 NOTIONAL VALUE FAIR VALUE NOTIONAL VALUE FAIR VALUE (In Millions) ASSET (1) LIABILITY (2) ASSET (1) LIABILITY (2) Derivatives Designated as Hedging under GAAP Interest Rate Contracts Fair Value Hedges $ 9,466.4 $ 182.4 $ 420.1 $ 7,042.7 $ 94.7 $ 71.0 Foreign Exchange Contracts Cash Flow Hedges 164.9 4.0 — 1,453.6 15.0 42.2 Net Investment Hedges 4,086.7 21.2 0.8 4,077.4 13.3 31.9 Total Derivatives Designated as Hedging under GAAP $ 13,718.0 $ 207.6 $ 420.9 $ 12,573.7 $ 123.0 $ 145.1 Derivatives Not Designated as Hedging under GAAP Non-Designated Risk Management Derivatives Foreign Exchange Contracts $ — $ — $ — $ 20.7 $ — $ 0.1 Other Financial Derivatives (3) 930.4 — 21.0 867.9 — 25.4 Total Non-Designated Risk Management Derivatives $ 930.4 $ — $ 21.0 $ 888.6 $ — $ 25.5 Client-Related and Trading Derivatives Foreign Exchange Contracts $ 317,051.6 $ 1,331.9 $ 1,317.3 $ 313,336.9 $ 3,238.4 $ 3,181.0 Interest Rate Contracts 15,892.9 221.6 57.8 13,584.1 206.8 298.2 Total Client-Related and Trading Derivatives $ 332,944.5 $ 1,553.5 $ 1,375.1 $ 326,921.0 $ 3,445.2 $ 3,479.2 Total Derivatives Not Designated as Hedging under GAAP $ 333,874.9 $ 1,553.5 $ 1,396.1 $ 327,809.6 $ 3,445.2 $ 3,504.7 Total Gross Derivatives $ 347,592.9 $ 1,761.1 $ 1,817.0 $ 340,383.3 $ 3,568.2 $ 3,649.8 Less: Netting (4) 914.2 1,070.1 3,126.7 2,205.4 Total Derivative Financial Instruments $ 846.9 $ 746.9 $ 441.5 $ 1,444.4 (1) Derivative assets are reported in Other Assets on the consolidated balance sheets. (2) Derivative liabilities are reported in Other Liabilities on the consolidated balance sheets. (3) Includes swaps related to sales of certain Visa Class B common shares. (4) See further detail in Note 23—Offsetting of Assets and Liabilities.
Cash Flow Hedge Derivative Gains and Losses Recognized in AOCI and Reclassified to Income	The following tables provide fair value and cash flow hedge derivative gains and losses recognized in income during the three month periods ended March 31, 2024 and 2023. TABLE 71: LOCATION AND AMOUNT OF FAIR VALUE AND CASH FLOW HEDGE DERIVATIVE GAINS AND LOSSES RECORDED IN INCOME (In Millions) INTEREST INCOME INTEREST EXPENSE OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, 2024 2023 2024 2023 2024 2023 Total amounts on the consolidated statements of income $ 2,445.6 $ 1,455.4 $ 1,917.5 $ 924.2 $ 61.0 $ 46.8 Gains (Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives 123.0 (18.5) (30.1) 49.1 — — Recognized on hedged items (123.0) 18.5 30.1 (49.1) — — Amounts related to interest settlements on derivatives 22.3 12.3 (19.9) (18.4) — — Total gains (losses) recognized on fair value hedges $ 22.3 $ 12.3 $ (19.9) $ (18.4) $ — $ — Gains (Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gains (losses) reclassified from AOCI to net income $ 5.5 $ — $ — $ — $ — $ 0.6 Total gains (losses) reclassified from AOCI to net income on cash flow hedges $ 5.5 $ — $ — $ — $ — $ 0.6
Location and Amount of Fair Value Hedge Derivative Gains and Losses Recorded in Income	The following table provides the impact of fair value hedge accounting on the carrying value of the designated hedged items as of March 31, 2024 and December 31, 2023. TABLE 72: HEDGED ITEMS IN FAIR VALUE HEDGES MARCH 31, 2024 DECEMBER 31, 2023 (In Millions) CARRYING VALUE OF THE HEDGED ITEMS CUMULATIVE HEDGE ACCOUNTING BASIS ADJUSTMENT (1)(3) CARRYING VALUE OF THE HEDGED ITEMS CUMULATIVE HEDGE ACCOUNTING BASIS ADJUSTMENT (2)(3) Available for Sale Debt Securities (4) $ 7,319.0 $ (45.5) $ 5,048.8 $ 77.5 Senior Notes and Long-Term Subordinated Debt 2,469.9 (274.8) 2,495.9 (248.7) (1) The cumulative hedge accounting basis adjustment includes $2.1 million related to discontinued hedging relationships of AFS debt securities and $25.6 million related to discontinued hedging relationships in the cumulative hedge accounting basis adjustment of senior notes and long-term debt as of March 31, 2024. (2) The cumulative hedge accounting basis adjustment includes $2.2 million related to discontinued hedging relationships of AFS debt securities and $29.6 million related to discontinued hedging relationships in the cumulative hedge accounting basis adjustment of senior notes and long-term debt as of December 31, 2023. (3) Positive (negative) amounts related to AFS securities represent cumulative fair value hedge basis adjustments that will reduce (increase) net interest income in future periods. Positive (negative) amounts related to Senior Notes and Long-Term Subordinated Debt represent cumulative fair value hedge basis adjustments that will increase (reduce) net interest income in future periods. (4) Carrying value represents amortized cost.
Location and Amount of Gains and Losses Recorded in Income for Non-Designated Risk Management Derivative Instruments	The following table provides the location and amount of gains and losses recorded in the consolidated statements of income for the three and three months ended March 31, 2024 and 2023 for derivative instruments not designated as hedges under GAAP. TABLE 73: LOCATION AND AMOUNT OF GAINS AND LOSSES RECORDED IN INCOME FOR DERIVATIVES NOT DESIGNATED AS HEDGING UNDER GAAP (In Millions) DERIVATIVE GAINS (LOSSES) LOCATION RECOGNIZED IN INCOME AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME THREE MONTHS ENDED MARCH 31, 2024 2023 Non-designated risk management derivatives Foreign Exchange Contracts Other Operating Income $ (0.2) $ 0.7 Other Financial Derivatives (1) Other Operating Income (1.2) (8.8) Gains (Losses) from non-designated risk management derivatives $ (1.4) $ (8.1) Client-related and trading derivatives Foreign Exchange Contracts Foreign Exchange Trading Income $ 57.0 $ 53.0 Interest Rate Contracts Security Commissions and Trading Income 1.2 2.5 Gains from client-related and trading derivatives $ 58.2 $ 55.5 Total gains from derivatives not designated as hedging under GAAP $ 56.8 $ 47.4 (1) Includes swaps related to the sale of certain Visa Class B common shares.

Securities Sold Under Agreeme_2

Securities Sold Under Agreements to Repurchase (Tables)	3 Months Ended
	Mar. 31, 2024
Banking and Thrift, Other Disclosure [Abstract]
Repurchase Agreements Accounted for as Secured Borrowings	The following table provides information regarding repurchase agreements that are accounted for as secured borrowings as of March 31, 2024 and December 31, 2023. TABLE 74: REPURCHASE AGREEMENTS ACCOUNTED FOR AS SECURED BORROWINGS REMAINING CONTRACTUAL MATURITY OF THE AGREEMENTS MARCH 31, 2024 DECEMBER 31, 2023 (In Millions) OVERNIGHT AND CONTINUOUS U.S. Treasury and Agency Securities $ 511.4 $ 784.7 Total Borrowings 511.4 784.7 Net Amount of Recognized Liabilities for Repurchase Agreements in Note 23 511.4 784.7

Offsetting of Assets and Liab_2

Offsetting of Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell	The following table provides information regarding the offsetting of derivative assets and securities purchased under agreements to resell within the consolidated balance sheets as of March 31, 2024 and December 31, 2023. TABLE 75: OFFSETTING OF DERIVATIVE ASSETS AND SECURITIES PURCHASED UNDER AGREEMENTS TO RESELL MARCH 31, 2024 (In Millions) GROSS RECOGNIZED ASSETS GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (3) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET (4) NET AMOUNT (5) Derivative Assets (1) Foreign Exchange Contracts Over the Counter (OTC) $ 923.3 $ 699.0 $ 224.3 $ 3.6 $ 220.7 Interest Rate Swaps OTC 399.5 215.2 184.3 — 184.3 Interest Rate Swaps Exchange Cleared 4.5 — 4.5 — 4.5 Total Derivatives Subject to a Master Netting Arrangement 1,327.3 914.2 413.1 3.6 409.5 Total Derivatives Not Subject to a Master Netting Arrangement 433.8 — 433.8 — 433.8 Total Derivatives 1,761.1 914.2 846.9 3.6 843.3 Securities Purchased under Agreements to Resell (2) $ 66,364.6 $ 65,864.5 $ 500.1 $ 500.1 $ — DECEMBER 31, 2023 (In Millions) GROSS RECOGNIZED ASSETS GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (3) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET (4) NET AMOUNT (5) Derivative Assets (1) Foreign Exchange Contracts OTC $ 3,006.3 $ 2,937.2 $ 69.1 $ 12.2 $ 56.9 Interest Rate Swaps OTC 301.4 189.5 111.9 — 111.9 Interest Rate Swaps Exchange Cleared 0.1 — 0.1 — 0.1 Total Derivatives Subject to a Master Netting Arrangement 3,307.8 3,126.7 181.1 12.2 168.9 Total Derivatives Not Subject to a Master Netting Arrangement 260.4 — 260.4 — 260.4 Total Derivatives 3,568.2 3,126.7 441.5 12.2 429.3 Securities Purchased under Agreements to Resell (2) $ 62,860.2 $ 62,075.5 $ 784.7 $ 784.7 $ — (1) Derivative assets are reported in Other Assets on the consolidated balance sheets. Other Assets (excluding derivative assets) totaled $10.2 billion and $10.3 billion as of March 31, 2024 and December 31, 2023, respectively. (2) Offsetting of Securities Purchased under Agreements to Resell primarily relates to our involvement in the FICC. (3) Including cash collateral received from counterparties. (4) Including financial assets accepted as collateral which are received from counterparties. (5) Northern Trust did not possess any cash collateral that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2024 and December 31, 2023.
Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase	The following table provides information regarding the offsetting of derivative liabilities and securities sold under agreements to repurchase within the consolidated balance sheets as of March 31, 2024 and December 31, 2023. TABLE 76: OFFSETTING OF DERIVATIVE LIABILITIES AND SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE MARCH 31, 2024 (In Millions) GROSS RECOGNIZED LIABILITIES GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (3) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET (4) NET AMOUNT (5) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 1,131.3 $ 1,051.2 $ 80.1 $ — $ 80.1 Interest Rate Swaps OTC 477.7 2.7 475.0 — 475.0 Interest Rate Swaps Exchange Cleared 0.2 — 0.2 — 0.2 Other Financial Derivatives 21.0 16.2 4.8 — 4.8 Total Derivatives Subject to a Master Netting Arrangement 1,630.2 1,070.1 560.1 — 560.1 Total Derivatives Not Subject to a Master Netting Arrangement 186.8 — 186.8 — 186.8 Total Derivatives 1,817.0 1,070.1 746.9 — 746.9 Securities Sold under Agreements to Repurchase (2) $ 66,375.9 $ 65,864.5 $ 511.4 $ 511.4 $ — DECEMBER 31, 2023 (In Millions) GROSS RECOGNIZED LIABILITIES GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (3) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET (4) NET AMOUNT (5) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 2,411.7 $ 2,175.7 $ 236.0 $ — $ 236.0 Interest Rate Swaps OTC 368.3 6.0 362.3 — 362.3 Interest Rate Swaps Exchange Cleared 0.9 — 0.9 — 0.9 Other Financial Derivatives 25.4 23.7 1.7 — 1.7 Total Derivatives Subject to a Master Netting Arrangement 2,806.3 2,205.4 600.9 — 600.9 Total Derivatives Not Subject to a Master Netting Arrangement 843.5 — 843.5 — 843.5 Total Derivatives 3,649.8 2,205.4 1,444.4 — 1,444.4 Securities Sold under Agreements to Repurchase (2) $ 62,860.2 $ 62,075.5 $ 784.7 $ 784.7 $ — (1) Derivative liabilities are reported in Other Liabilities on the consolidated balance sheets. Other Liabilities (excluding derivative liabilities) totaled $2.9 billion and $4.0 billion as of March 31, 2024 and December 31, 2023, respectively. (2) Offsetting of Securities Sold under Agreements to Repurchase primarily relates to our involvement in the FICC. (3) Including cash collateral deposited with counterparties. (4) Including financial assets accepted as collateral which are deposited with counterparties. (5) Northern Trust did not place any cash collateral with counterparties that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2024 and December 31, 2023.

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) shares in Millions, $ in Millions	Mar. 31, 2024 USD ($) security	Dec. 31, 2023 USD ($) security	Jun. 30, 2016 shares	Jun. 30, 2015 shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for Sale	$ 25,638.9	$ 23,089.8
Visa Class B
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Shares issued (in shares) | shares			1.1	1
LEVEL 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of available for sale securities portfolio | security	910	929
Available for Sale	$ 19,500	$ 19,500
LEVEL 3 | Fair Value, Measurements, Nonrecurring | Measurement Input, Discount Rate | Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input		0
LEVEL 3 | Fair Value, Measurements, Nonrecurring | Measurement Input, Discount Rate | Upper Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input		0.200
LEVEL 3 | Fair Value, Measurements, Nonrecurring | Measurement Input, Discount Rate | WEIGHTED-AVERAGE INPUT VALUES
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input		0.020
LEVEL 3 | Fair Value, Measurements, Nonrecurring | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 0.1

Fair Value Measurements (Level

Fair Value Measurements (Level 3 Significant Unobservable Inputs) (Details) $ in Millions	Mar. 31, 2024 USD ($) month	Dec. 31, 2023 USD ($) month
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities | $	$ 746.9	$ 1,444.4
Swap | Fair Value, Measurements, Recurring | LEVEL 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities | $	$ 21	$ 25.4
Swap | Conversion Rate | Fair Value, Measurements, Recurring | LEVEL 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, measurement input	1.59	1.59
Swap | Visa Class A Appreciation | Fair Value, Measurements, Recurring | LEVEL 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, measurement input	0.0922	0.1049
Swap | Expected Duration | Fair Value, Measurements, Recurring | LEVEL 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, measurement input	10	13
Swap | Expected Duration | Fair Value, Measurements, Recurring | LEVEL 3 | Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, measurement input	6	9
Swap | Expected Duration | Fair Value, Measurements, Recurring | LEVEL 3 | Upper Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liability, measurement input	24	27

Fair Value Measurements (Recurr

Fair Value Measurements (Recurring Basis Hierarchy Leveling) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	$ 25,638.9	$ 23,089.8
Derivative Assets	1,761.1	3,568.2
NETTING	(914.2)	(3,126.7)
Derivative Assets	846.9	441.5
Derivative Liabilities	1,817	3,649.8
NETTING	(1,070.1)	(2,205.4)
Derivative Liabilities	746.9	1,444.4
Cross Product Collateral Adjustment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(181)	(2,093.8)
NETTING	(336.9)	(1,172.5)
U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,112.3	3,622.2
Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	295	295.8
Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	12,351.4	11,553
Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	307.6	264.4
Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	250.2	279.5
Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	296.8	347.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,860.8	2,899.9
Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,523	2,962.6
Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	641.8	865.3
LEVEL 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	19,500	19,500
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	25,638.9	23,089.8
Trading Account		0
Total Available for Sale Debt Securities		23,089.8
Fair Value, Measurements, Recurring | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,112.3	3,622.2
Fair Value, Measurements, Recurring | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	295	295.8
Fair Value, Measurements, Recurring | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	12,351.4	11,553
Fair Value, Measurements, Recurring | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	307.6	264.4
Fair Value, Measurements, Recurring | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	250.2	279.5
Fair Value, Measurements, Recurring | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	296.8	347.1
Fair Value, Measurements, Recurring | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,860.8	2,899.9
Fair Value, Measurements, Recurring | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,523	2,962.6
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	641.8	865.3
Fair Value, Measurements, Recurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money Market Investment	95	95
NETTING	(914.2)	(3,126.7)
Derivative Assets	846.9	441.5
Fair Value, Measurements, Recurring | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(699)	(2,937.2)
Derivative Assets	658.1	329.5
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(215.2)	(189.5)
Derivative Assets	188.8	112
Fair Value, Measurements, Recurring | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(1,070.1)	(2,205.4)
Derivative Liabilities	746.9	1,444.4
Fair Value, Measurements, Recurring | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(1,051.2)	(2,175.7)
Derivative Liabilities	266.9	1,079.5
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(2.7)	(6)
Derivative Liabilities	475.2	363.2
Fair Value, Measurements, Recurring | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(16.2)	(23.7)
Derivative Liabilities	4.8	1.7
Fair Value, Measurements, Recurring | LEVEL 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,112.3	3,622.2
Trading Account		0
Total Available for Sale Debt Securities		3,622.2
Fair Value, Measurements, Recurring | LEVEL 1 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	6,112.3	3,622.2
Fair Value, Measurements, Recurring | LEVEL 1 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money Market Investment	95	95
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	19,526.6	19,467.6
Trading Account		0
Total Available for Sale Debt Securities		19,467.6
Fair Value, Measurements, Recurring | LEVEL 2 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 2 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	295	295.8
Fair Value, Measurements, Recurring | LEVEL 2 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	12,351.4	11,553
Fair Value, Measurements, Recurring | LEVEL 2 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	307.6	264.4
Fair Value, Measurements, Recurring | LEVEL 2 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	250.2	279.5
Fair Value, Measurements, Recurring | LEVEL 2 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	296.8	347.1
Fair Value, Measurements, Recurring | LEVEL 2 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,860.8	2,899.9
Fair Value, Measurements, Recurring | LEVEL 2 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,523	2,962.6
Fair Value, Measurements, Recurring | LEVEL 2 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	641.8	865.3
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money Market Investment	0	0
Derivative Assets	1,761.1	3,568.2
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	1,357.1	3,266.7
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	404	301.5
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	1,796	3,624.4
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	1,318.1	3,255.2
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	477.9	369.2
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Trading Account		0
Total Available for Sale Debt Securities		0
Fair Value, Measurements, Recurring | LEVEL 3 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money Market Investment	0	0
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	21	25.4
Fair Value, Measurements, Recurring | LEVEL 3 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	$ 21	$ 25.4

Fair Value Measurements (Change

Fair Value Measurements (Changes in Level 3 Liabilities) (Details) - SWAPS RELATED TO SALE OF CERTAIN VISA CLASS B COMMON SHARES - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value liabilities beginning balance	$ 25.4	$ 34.8
Total (Gains) Losses:
Included in Earnings	1.2	7.6
Purchases, Issues, Sales, and Settlements
Settlements	(5.5)	(7.8)
Fair value liabilities ending balance	$ 21.1	$ 34.6

Fair Value Measurements (Nonrec

Fair Value Measurements (Nonrecurring Basis Significant Unobservable Inputs) (Details) - Fair Value, Measurements, Nonrecurring - LEVEL 3 $ in Millions	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FAIR VALUE	$ 0.1
Measurement Input, Discount Rate | Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input		0
Measurement Input, Discount Rate | Upper Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input		0.200
Measurement Input, Discount Rate | WEIGHTED-AVERAGE INPUT VALUES
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input		0.020
Loans | Measurement Input, Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FAIR VALUE	$ 0.1	$ 43.3

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
ASSETS
Cash and Due from Banks	$ 5,308,700,000	$ 4,791,500,000
Federal Reserve and Other Central Bank Deposits	40,269,900,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,372,100,000	1,939,000,000
Securities Purchased under Agreements to Resell	500,100,000	784,700,000
Debt Securities - Held to Maturity	21,641,400,000	24,473,000,000
Loans
Deposits	123,941,700,000	116,164,000,000
Deposits
Savings Certificates and Other Time	5,636,600,000	4,109,700,000
Non U.S. Offices — Interest-Bearing	67,084,700,000	63,971,100,000
Federal Funds Purchased	2,600,500,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	511,400,000	784,700,000
Other Borrowings	6,526,200,000	6,567,800,000
Senior Notes	2,743,500,000	2,773,200,000
Unfunded Commitments	0
TOTAL ESTIMATED FAIR VALUE
ASSETS
Cash and Due from Banks	5,308,700,000	4,791,500,000
Federal Reserve and Other Central Bank Deposits	40,269,900,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,372,100,000	1,939,000,000
Securities Purchased under Agreements to Resell	500,100,000	784,700,000
Debt Securities - Held to Maturity	21,641,400,000	24,473,000,000
Loans
Held for Investment	47,179,400,000	47,598,300,000
Other Assets	1,490,300,000	1,458,000,000
Deposits	123,996,600,000	116,207,600,000
Deposits
Federal Funds Purchased	2,600,500,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	511,400,000	784,700,000
Other Borrowings	6,544,300,000	6,607,400,000
Senior Notes	2,771,300,000	2,798,100,000
Long-Term Debt	4,135,700,000	4,186,800,000
Unfunded Commitments	163,300,000	178,800,000
Other Liabilities	42,700,000	74,900,000
TOTAL ESTIMATED FAIR VALUE | LEVEL 1
ASSETS
Cash and Due from Banks	5,308,700,000	4,791,500,000
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	0
Loans
Held for Investment	0	0
Other Assets	95,200,000	86,100,000
Deposits	0	0
Deposits
Federal Funds Purchased	0	0
Securities Sold Under Agreements to Repurchase	0	0
Other Borrowings	0	0
Senior Notes	0	0
Long-Term Debt	0	0
Unfunded Commitments	0	0
Other Liabilities	0	0
TOTAL ESTIMATED FAIR VALUE | LEVEL 2
ASSETS
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	40,269,900,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,372,100,000	1,939,000,000
Securities Purchased under Agreements to Resell	500,100,000	784,700,000
Debt Securities - Held to Maturity	21,641,400,000	24,473,000,000
Loans
Held for Investment	0	0
Other Assets	1,395,100,000	1,371,900,000
Deposits	123,996,600,000	116,207,600,000
Deposits
Federal Funds Purchased	2,600,500,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	511,400,000	784,700,000
Other Borrowings	6,544,300,000	6,607,400,000
Senior Notes	2,771,300,000	2,798,100,000
Long-Term Debt	4,135,700,000	4,186,800,000
Unfunded Commitments	163,300,000	178,800,000
Other Liabilities	0	0
TOTAL ESTIMATED FAIR VALUE | LEVEL 3
ASSETS
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	0
Loans
Held for Investment	47,179,400,000	47,598,300,000
Other Assets	0	0
Deposits	0	0
Deposits
Federal Funds Purchased	0	0
Securities Sold Under Agreements to Repurchase	0	0
Other Borrowings	0	0
Senior Notes	0	0
Long-Term Debt	0	0
Unfunded Commitments	0	0
Other Liabilities	42,700,000	74,900,000
BOOK VALUE
ASSETS
Cash and Due from Banks	5,308,700,000	4,791,500,000
Federal Reserve and Other Central Bank Deposits	40,269,900,000	34,326,200,000
Interest-Bearing Deposits with Banks	1,372,100,000	1,939,000,000
Securities Purchased under Agreements to Resell	500,100,000	784,700,000
Debt Securities - Held to Maturity	23,497,900,000	26,221,700,000
Loans
Held for Investment	47,180,100,000	47,438,300,000
Other Assets	1,505,700,000	1,476,600,000
Deposits	123,941,700,000	116,164,000,000
Deposits
Federal Funds Purchased	2,600,500,000	3,045,400,000
Securities Sold Under Agreements to Repurchase	511,400,000	784,700,000
Other Borrowings	6,526,200,000	6,567,800,000
Senior Notes	2,743,500,000	2,773,200,000
Long-Term Debt	4,069,000,000	4,065,000,000
Unfunded Commitments	163,300,000	178,800,000
Other Liabilities	$ 42,700,000	$ 74,900,000

Securities (Reconciliation of A

Securities (Reconciliation of Amortized Cost to Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Summary of Investment Holdings [Line Items]
AMORTIZED COST	$ 25,941.9	$ 23,659
GROSS UNREALIZED GAINS	29.7	13.2
GROSS UNREALIZED LOSSES	332.7	582.4
FAIR VALUE	25,638.9	23,089.8
U.S. Government
Summary of Investment Holdings [Line Items]
AMORTIZED COST	6,121.6	3,681.5
GROSS UNREALIZED GAINS	11	2.2
GROSS UNREALIZED LOSSES	20.3	61.5
FAIR VALUE	6,112.3	3,622.2
Obligations of States and Political Subdivisions
Summary of Investment Holdings [Line Items]
AMORTIZED COST	309.6	315.8
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	14.6	20
FAIR VALUE	295	295.8
Government Sponsored Agency
Summary of Investment Holdings [Line Items]
AMORTIZED COST	12,501.9	11,744.3
GROSS UNREALIZED GAINS	12.5	9
GROSS UNREALIZED LOSSES	163	200.3
FAIR VALUE	12,351.4	11,553
Non-U.S. Government
Summary of Investment Holdings [Line Items]
AMORTIZED COST	325	284.8
GROSS UNREALIZED GAINS	0.1	0
GROSS UNREALIZED LOSSES	17.5	20.4
FAIR VALUE	307.6	264.4
Corporate Debt
Summary of Investment Holdings [Line Items]
AMORTIZED COST	256.5	287.5
GROSS UNREALIZED GAINS	0.2	0.1
GROSS UNREALIZED LOSSES	6.5	8.1
FAIR VALUE	250.2	279.5
Covered Bonds
Summary of Investment Holdings [Line Items]
AMORTIZED COST	302.7	356.8
GROSS UNREALIZED GAINS	0.3	0
GROSS UNREALIZED LOSSES	6.2	9.7
FAIR VALUE	296.8	347.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Summary of Investment Holdings [Line Items]
AMORTIZED COST	2,912.6	3,013.8
GROSS UNREALIZED GAINS	3.8	0.1
GROSS UNREALIZED LOSSES	55.6	114
FAIR VALUE	2,860.8	2,899.9
Other Asset-Backed
Summary of Investment Holdings [Line Items]
AMORTIZED COST	2,552.4	3,061
GROSS UNREALIZED GAINS	1.6	1.6
GROSS UNREALIZED LOSSES	31	100
FAIR VALUE	2,523	2,962.6
Commercial Mortgage-Backed
Summary of Investment Holdings [Line Items]
AMORTIZED COST	659.6	913.5
GROSS UNREALIZED GAINS	0.2	0.2
GROSS UNREALIZED LOSSES	18	48.4
FAIR VALUE	$ 641.8	$ 865.3

Securities (Remaining Maturity

Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Available for Sale - Amortized Cost
ONE YEAR OR LESS	$ 3,580.8
ONE TO FIVE YEARS	14,894.2
FIVE TO TEN YEARS	6,364.3
OVER TEN YEARS	1,102.6
AMORTIZED COST	25,941.9	$ 23,659
Available for Sale - Fair Value
ONE YEAR OR LESS	3,542.3
ONE TO FIVE YEARS	14,718.3
FIVE TO TEN YEARS	6,302.4
OVER TEN YEARS	1,075.9
FAIR VALUE	25,638.9	23,089.8
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	4,875.7
ONE TO FIVE YEARS	11,941.7
FIVE TO TEN YEARS	4,564
OVER TEN YEARS	2,116.5
Amortized Cost	23,497.9	26,221.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	4,732.5
ONE TO FIVE YEARS	11,050.2
FIVE TO TEN YEARS	4,113.8
OVER TEN YEARS	1,744.9
Fair Value	21,641.4	24,473
U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	348.1
ONE TO FIVE YEARS	3,422
FIVE TO TEN YEARS	2,351.5
OVER TEN YEARS	0
AMORTIZED COST	6,121.6	3,681.5
Available for Sale - Fair Value
ONE YEAR OR LESS	344.2
ONE TO FIVE YEARS	3,412.9
FIVE TO TEN YEARS	2,355.2
OVER TEN YEARS	0
FAIR VALUE	6,112.3	3,622.2
Held to Maturity - Amortized Cost
Amortized Cost		0
Obligations of States and Political Subdivisions
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0
ONE TO FIVE YEARS	111.2
FIVE TO TEN YEARS	198.4
OVER TEN YEARS	0
AMORTIZED COST	309.6	315.8
Available for Sale - Fair Value
ONE YEAR OR LESS	0
ONE TO FIVE YEARS	106.5
FIVE TO TEN YEARS	188.5
OVER TEN YEARS	0
FAIR VALUE	295	295.8
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	60.4
ONE TO FIVE YEARS	1,206.8
FIVE TO TEN YEARS	1,039.9
OVER TEN YEARS	264.5
Amortized Cost	2,571.6	2,563.9
Held to Maturity - Fair Value
ONE YEAR OR LESS	60
ONE TO FIVE YEARS	1,174.1
FIVE TO TEN YEARS	998.1
OVER TEN YEARS	250.2
Fair Value	2,482.4	2,492
Government Sponsored Agency
Available for Sale - Amortized Cost
ONE YEAR OR LESS	2,631.6
ONE TO FIVE YEARS	5,460.5
FIVE TO TEN YEARS	3,409.8
OVER TEN YEARS	1,000
AMORTIZED COST	12,501.9	11,744.3
Available for Sale - Fair Value
ONE YEAR OR LESS	2,606.9
ONE TO FIVE YEARS	5,396.1
FIVE TO TEN YEARS	3,375.2
OVER TEN YEARS	973.2
FAIR VALUE	12,351.4	11,553
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	990.3
ONE TO FIVE YEARS	3,419.8
FIVE TO TEN YEARS	3,138.9
OVER TEN YEARS	1,674.3
Amortized Cost	9,223.3	9,355.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	883.6
ONE TO FIVE YEARS	3,038.5
FIVE TO TEN YEARS	2,768.6
OVER TEN YEARS	1,435
Fair Value	8,125.7	8,345.2
Non-U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	64.8
ONE TO FIVE YEARS	260.2
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
AMORTIZED COST	325	284.8
Available for Sale - Fair Value
ONE YEAR OR LESS	63.5
ONE TO FIVE YEARS	244.1
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
FAIR VALUE	307.6	264.4
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	1,569.9
ONE TO FIVE YEARS	1,139.3
FIVE TO TEN YEARS	32.9
OVER TEN YEARS	0
Amortized Cost	2,742.1	4,789.1
Held to Maturity - Fair Value
ONE YEAR OR LESS	1,564.7
ONE TO FIVE YEARS	1,056.5
FIVE TO TEN YEARS	28.7
OVER TEN YEARS	0
Fair Value	2,649.9	4,698.6
Corporate Debt
Available for Sale - Amortized Cost
ONE YEAR OR LESS	103.1
ONE TO FIVE YEARS	153.4
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
AMORTIZED COST	256.5	287.5
Available for Sale - Fair Value
ONE YEAR OR LESS	102.3
ONE TO FIVE YEARS	147.9
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
FAIR VALUE	250.2	279.5
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	247.8
ONE TO FIVE YEARS	347.3
FIVE TO TEN YEARS	15.2
OVER TEN YEARS	0
Amortized Cost	610.3	646.1
Held to Maturity - Fair Value
ONE YEAR OR LESS	243
ONE TO FIVE YEARS	329.8
FIVE TO TEN YEARS	12.8
OVER TEN YEARS	0
Fair Value	585.6	617.9
Covered Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	66.4
ONE TO FIVE YEARS	236.3
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
AMORTIZED COST	302.7	356.8
Available for Sale - Fair Value
ONE YEAR OR LESS	65.9
ONE TO FIVE YEARS	230.9
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
FAIR VALUE	296.8	347.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	493.8
ONE TO FIVE YEARS	1,389.9
FIVE TO TEN YEARS	226.6
OVER TEN YEARS	0
Amortized Cost	2,110.3	2,208.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	492.7
ONE TO FIVE YEARS	1,310.4
FIVE TO TEN YEARS	204.1
OVER TEN YEARS	0
Fair Value	2,007.2	2,100.6
Certificates of Deposit
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	403.2
ONE TO FIVE YEARS	0
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
Amortized Cost	403.2	585.1
Held to Maturity - Fair Value
ONE YEAR OR LESS	403
ONE TO FIVE YEARS	0
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
Fair Value	403	584.4
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	126.8
ONE TO FIVE YEARS	2,564.7
FIVE TO TEN YEARS	221.1
OVER TEN YEARS	0
AMORTIZED COST	2,912.6	3,013.8
Available for Sale - Fair Value
ONE YEAR OR LESS	125.4
ONE TO FIVE YEARS	2,525.9
FIVE TO TEN YEARS	209.5
OVER TEN YEARS	0
FAIR VALUE	2,860.8	2,899.9
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	1,058.4
ONE TO FIVE YEARS	3,960.5
FIVE TO TEN YEARS	5.6
OVER TEN YEARS	0
Amortized Cost	5,024.5	5,245.5
Held to Maturity - Fair Value
ONE YEAR OR LESS	1,035.1
ONE TO FIVE YEARS	3,697.1
FIVE TO TEN YEARS	4.5
OVER TEN YEARS	0
Fair Value	4,736.7	4,953.8
Other Asset-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	218.3
ONE TO FIVE YEARS	2,108.8
FIVE TO TEN YEARS	122.7
OVER TEN YEARS	102.6
AMORTIZED COST	2,552.4	3,061
Available for Sale - Fair Value
ONE YEAR OR LESS	213.5
ONE TO FIVE YEARS	2,083.8
FIVE TO TEN YEARS	123
OVER TEN YEARS	102.7
FAIR VALUE	2,523	2,962.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	1.2
ONE TO FIVE YEARS	120.7
FIVE TO TEN YEARS	71.8
OVER TEN YEARS	0
Amortized Cost	193.7	214.2
Held to Maturity - Fair Value
ONE YEAR OR LESS	1.2
ONE TO FIVE YEARS	121.5
FIVE TO TEN YEARS	72.1
OVER TEN YEARS	0
Fair Value	194.8	214.4
Other
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	50.7
ONE TO FIVE YEARS	319.8
FIVE TO TEN YEARS	33.1
OVER TEN YEARS	177.7
Amortized Cost	581.3	576.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	49.2
ONE TO FIVE YEARS	285
FIVE TO TEN YEARS	24.9
OVER TEN YEARS	59.7
Fair Value	418.8	429.3
Commercial Mortgage-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	21.7
ONE TO FIVE YEARS	577.1
FIVE TO TEN YEARS	60.8
OVER TEN YEARS	0
AMORTIZED COST	659.6	913.5
Available for Sale - Fair Value
ONE YEAR OR LESS	20.6
ONE TO FIVE YEARS	570.2
FIVE TO TEN YEARS	51
OVER TEN YEARS	0
FAIR VALUE	641.8	865.3
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	0
ONE TO FIVE YEARS	37.6
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
Amortized Cost	37.6	37.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	0
ONE TO FIVE YEARS	37.3
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
Fair Value	$ 37.3	$ 36.8

Securities (Securities with Unr

Securities (Securities with Unrealized Losses) (Details) $ in Millions	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($) Security
FAIR VALUE
LESS THAN 12 MONTHS	$ 818.4	$ 503
12 MONTHS OR LONGER	12,703.2	18,932.3
TOTAL	13,521.6	19,435.3
UNREALIZED LOSSES
LESS THAN 12 MONTHS	43.3	24.1
12 MONTHS OR LONGER	284.7	544.2
TOTAL	328	568.3
U.S. Government
FAIR VALUE
LESS THAN 12 MONTHS	87.4	0
12 MONTHS OR LONGER	819.5	3,364.7
TOTAL	906.9	3,364.7
UNREALIZED LOSSES
LESS THAN 12 MONTHS	12	0
12 MONTHS OR LONGER	8.3	61.5
TOTAL	20.3	61.5
Obligations of States and Political Subdivisions
FAIR VALUE
LESS THAN 12 MONTHS	295	87.8
12 MONTHS OR LONGER	0	208
TOTAL	295	295.8
UNREALIZED LOSSES
LESS THAN 12 MONTHS	14.6	5.9
12 MONTHS OR LONGER	0	14.1
TOTAL	14.6	20
Government Sponsored Agency
FAIR VALUE
LESS THAN 12 MONTHS	145.3	331
12 MONTHS OR LONGER	8,865.2	9,486.6
TOTAL	9,010.5	9,817.6
UNREALIZED LOSSES
LESS THAN 12 MONTHS	7.9	11.5
12 MONTHS OR LONGER	155.1	188.8
TOTAL	163	200.3
Non-U.S. Government
FAIR VALUE
LESS THAN 12 MONTHS	63.5	0
12 MONTHS OR LONGER	189.5	264.5
TOTAL	253	264.5
UNREALIZED LOSSES
LESS THAN 12 MONTHS	1.3	0
12 MONTHS OR LONGER	16.2	20.4
TOTAL	17.5	20.4
Corporate Debt
FAIR VALUE
LESS THAN 12 MONTHS	36.9	4.4
12 MONTHS OR LONGER	55.7	143
TOTAL	92.6	147.4
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0.9	0.1
12 MONTHS OR LONGER	0.9	2.1
TOTAL	1.8	$ 2.2
Number of debt securities, available-for-sale | Security		3
Debt securities, available-for-sale, continuous unrealized loss position with credit loss	80.1	$ 98.4
Debt securities, available-for-sale, continuous unrealized loss position, accumulated loss, with credit loss	4.7	5.9
Net amount of recognized liabilities for repurchase agreements	0.5	1.2
Covered Bonds
FAIR VALUE
LESS THAN 12 MONTHS	60.4	0
12 MONTHS OR LONGER	104.9	213.2
TOTAL	165.3	213.2
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0.5	0
12 MONTHS OR LONGER	5.7	9.7
TOTAL	6.2	9.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
FAIR VALUE
LESS THAN 12 MONTHS	110	0
12 MONTHS OR LONGER	1,066	2,477
TOTAL	1,176	2,477
UNREALIZED LOSSES
LESS THAN 12 MONTHS	5	0
12 MONTHS OR LONGER	50.6	105.8
TOTAL	55.6	$ 105.8
Number of debt securities, available-for-sale | Security		1
Debt securities, available-for-sale, continuous unrealized loss position with credit loss		$ 71
Debt securities, available-for-sale, continuous unrealized loss position, accumulated loss, with credit loss		8.2
Other Asset-Backed
FAIR VALUE
LESS THAN 12 MONTHS	13.9	19.8
12 MONTHS OR LONGER	995	1,998.7
TOTAL	1,008.9	2,018.5
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0.7	2
12 MONTHS OR LONGER	30.3	98
TOTAL	31	100
Commercial Mortgage-Backed
FAIR VALUE
LESS THAN 12 MONTHS	6	60
12 MONTHS OR LONGER	607.4	776.6
TOTAL	613.4	836.6
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0.4	4.6
12 MONTHS OR LONGER	17.6	43.8
TOTAL	$ 18	$ 48.4

Securities (Narrative) (Details

Securities (Narrative) (Details) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024 USD ($) investment	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($) investment
Debt and Equity Securities, FV-NI [Line Items]
Number of securities in an unrealized loss position | investment	784		898
Total fair value	$ 13,521.6		$ 19,435.3
Debt securities, unrealized losses	328		568.3
Investment Security Gains (Losses), net	189.4	$ (6.9)
Debt securities, available-for-sale, realized loss			176.4
Provision for (release of) credit losses	(7.8)	14.5
Held to maturity securities	23,497.9		26,221.7
Debt securities, held-to-maturity, accumulated unrecognized loss	$ 1,862.1		$ 1,755.6
Percentage of debt securities, held-to-maturity, portfolio	1		1
Moodys And Standard Poors A Or Higher Rating
Debt and Equity Securities, FV-NI [Line Items]
Percentage of debt securities, held-to-maturity, portfolio	0.96		0.97
BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	$ 326.2		$ 334
Percentage of debt securities, held-to-maturity, portfolio	0.01		0.01
NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	$ 576.6		$ 560.9
Percentage of debt securities, held-to-maturity, portfolio	0.03		0.02
Government Sponsored Agency
Debt and Equity Securities, FV-NI [Line Items]
Total fair value	$ 9,010.5		$ 9,817.6
Debt securities, unrealized losses	163		200.3
Investment Security Gains (Losses), net	23
Held to maturity securities	9,223.3		9,355.3
Debt securities, held-to-maturity, accumulated unrecognized loss	1,099.2		1,012.4
Government Sponsored Agency | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Government Sponsored Agency | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Obligations of States and Political Subdivisions
Debt and Equity Securities, FV-NI [Line Items]
Total fair value	295		295.8
Debt securities, unrealized losses	14.6		20
Investment Security Gains (Losses), net		(9.8)
Held to maturity securities	2,571.6		2,563.9
Debt securities, held-to-maturity, accumulated unrecognized loss	89.5		72.4
Obligations of States and Political Subdivisions | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Obligations of States and Political Subdivisions | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0.2
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Total fair value	92.6		147.4
Debt securities, unrealized losses	1.8		2.2
Investment Security Gains (Losses), net		1.2
Provision for (release of) credit losses	(0.7)	0.5
Net amount of recognized liabilities for repurchase agreements	0.5		1.2
Held to maturity securities	610.3		646.1
Debt securities, held-to-maturity, accumulated unrecognized loss	24.7		28.2
Proceeds from sale of investment securities	2,000	2,100
Corporate Debt | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Corporate Debt | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Commercial Mortgage-Backed
Debt and Equity Securities, FV-NI [Line Items]
Total fair value	613.4		836.6
Debt securities, unrealized losses	18		48.4
Investment Security Gains (Losses), net	22.6	0.9
Held to maturity securities	37.6		37.6
Debt securities, held-to-maturity, accumulated unrecognized loss	0.3		0.8
Commercial Mortgage-Backed | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Commercial Mortgage-Backed | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Other Asset-Backed
Debt and Equity Securities, FV-NI [Line Items]
Total fair value	1,008.9		2,018.5
Debt securities, unrealized losses	31		100
Investment Security Gains (Losses), net	56.6	$ 0.8
Held to maturity securities	193.7		214.2
Debt securities, held-to-maturity, accumulated unrecognized loss	0.2		0.2
Other Asset-Backed | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Other Asset-Backed | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
U.S. Government
Debt and Equity Securities, FV-NI [Line Items]
Total fair value	906.9		3,364.7
Debt securities, unrealized losses	20.3		61.5
Investment Security Gains (Losses), net	34.8
Held to maturity securities			0
U.S. Government | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities			0
U.S. Government | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities			0
Covered Bonds
Debt and Equity Securities, FV-NI [Line Items]
Total fair value	165.3		213.2
Debt securities, unrealized losses	6.2		9.7
Investment Security Gains (Losses), net	4.2
Held to maturity securities	2,110.3		2,208.6
Debt securities, held-to-maturity, accumulated unrecognized loss	103.8		108.3
Covered Bonds | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Covered Bonds | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	0		0
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Debt and Equity Securities, FV-NI [Line Items]
Total fair value	1,176		2,477
Debt securities, unrealized losses	55.6		105.8
Investment Security Gains (Losses), net	48.2
Held to maturity securities	5,024.5		5,245.5
Debt securities, held-to-maturity, accumulated unrecognized loss	289.4		294.9
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	1.1		1.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities	$ 0		$ 0

Securities (Reconciliation of_2

Securities (Reconciliation of Amortized Cost to Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 23,497.9	$ 26,221.7
GROSS UNREALIZED GAINS	5.6	6.9
GROSS UNREALIZED LOSSES	1,862.1	1,755.6
FAIR VALUE	21,641.4	24,473
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,571.6	2,563.9
GROSS UNREALIZED GAINS	0.3	0.5
GROSS UNREALIZED LOSSES	89.5	72.4
FAIR VALUE	2,482.4	2,492
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	9,223.3	9,355.3
GROSS UNREALIZED GAINS	1.6	2.3
GROSS UNREALIZED LOSSES	1,099.2	1,012.4
FAIR VALUE	8,125.7	8,345.2
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,742.1	4,789.1
GROSS UNREALIZED GAINS	0.1	0.2
GROSS UNREALIZED LOSSES	92.3	90.7
FAIR VALUE	2,649.9	4,698.6
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	610.3	646.1
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	24.7	28.2
FAIR VALUE	585.6	617.9
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,110.3	2,208.6
GROSS UNREALIZED GAINS	0.7	0.3
GROSS UNREALIZED LOSSES	103.8	108.3
FAIR VALUE	2,007.2	2,100.6
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	403.2	585.1
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	0.2	0.7
FAIR VALUE	403	584.4
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,024.5	5,245.5
GROSS UNREALIZED GAINS	1.6	3.2
GROSS UNREALIZED LOSSES	289.4	294.9
FAIR VALUE	4,736.7	4,953.8
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	193.7	214.2
GROSS UNREALIZED GAINS	1.3	0.4
GROSS UNREALIZED LOSSES	0.2	0.2
FAIR VALUE	194.8	214.4
Commercial Mortgage-Backed
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	37.6	37.6
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	0.3	0.8
FAIR VALUE	37.3	36.8
Other
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	581.3	576.3
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	162.5	147
FAIR VALUE	$ 418.8	$ 429.3

Securities (Credit Quality Indi

Securities (Credit Quality Indicators) (Details) $ in Millions	Mar. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 23,497.9	$ 26,221.7
Percent of Total	1	1
AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 17,669.4	$ 18,234.4
Percent of Total	0.75	0.70
AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 3,773.9	$ 4,257.7
Percent of Total	0.16	0.16
A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 1,151.8	$ 2,834.7
Percent of Total	0.05	0.11
BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 326.2	$ 334
Percent of Total	0.01	0.01
NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 576.6	$ 560.9
Percent of Total	0.03	0.02
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity		$ 0
U.S. Government | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity		0
U.S. Government | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity		0
U.S. Government | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity		0
U.S. Government | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity		0
U.S. Government | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity		0
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 2,571.6	2,563.9
Obligations of States and Political Subdivisions | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	956.9	954.7
Obligations of States and Political Subdivisions | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	1,614.7	1,609
Obligations of States and Political Subdivisions | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Obligations of States and Political Subdivisions | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Obligations of States and Political Subdivisions | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0.2
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	9,223.3	9,355.3
Government Sponsored Agency | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	9,223.3	9,355.3
Government Sponsored Agency | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Government Sponsored Agency | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Government Sponsored Agency | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Government Sponsored Agency | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	2,742.1	4,789.1
Non-U.S. Government | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	896.7	813.3
Non-U.S. Government | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	707.4	1,179.6
Non-U.S. Government | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	812.9	2,463.3
Non-U.S. Government | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	325.1	332.9
Non-U.S. Government | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	610.3	646.1
Corporate Debt | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	2.2	2.1
Corporate Debt | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	298.7	302.6
Corporate Debt | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	309.4	341.4
Corporate Debt | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Corporate Debt | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	2,110.3	2,208.6
Covered Bonds | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	2,110.3	2,208.6
Covered Bonds | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Covered Bonds | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Covered Bonds | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Covered Bonds | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	403.2	585.1
Certificates of Deposit | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	355.4	545.9
Certificates of Deposit | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Certificates of Deposit | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Certificates of Deposit | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Certificates of Deposit | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	47.8	39.2
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	5,024.5	5,245.5
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	3,840.8	4,047.9
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	1,153.1	1,166.5
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	29.5	30
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	1.1	1.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	193.7	214.2
Other Asset-Backed | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	193.7	214.2
Other Asset-Backed | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Other Asset-Backed | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Other Asset-Backed | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Other Asset-Backed | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Commercial Mortgage-Backed
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	37.6	37.6
Commercial Mortgage-Backed | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	37.6	37.6
Commercial Mortgage-Backed | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Commercial Mortgage-Backed | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Commercial Mortgage-Backed | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Commercial Mortgage-Backed | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Other
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	581.3	576.3
Other | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	52.5	54.8
Other | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Other | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Other | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0	0
Other | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 528.8	$ 521.5

Loans (Loans) (Details)

Loans (Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 47,342.6	$ 47,617
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	25,417.1	25,412.8
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	10,980.6	11,555.3
Commercial | Commercial and Institutional | Private Equity Funds
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	5,100	4,500
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	5,333	5,134.2
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	2,372.7	2,778.5
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	6,730.8	5,944.8
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	21,925.5	22,204.2
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	14,092.2	14,360
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	6,315.2	6,327.1
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	387.2	428.8
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 1,130.9	$ 1,088.3

Loans (Narrative) (Details)

Loans (Narrative) (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 47,342,600,000		$ 47,617,000,000
Other U.S. loans and non-U.S. loans, short duration advances	9,000,000,000		8,400,000,000
Demand deposits	10,700,000		12,100,000
Financing receivable, nonaccrual, interest income	700,000	$ 700,000
Loans in process of foreclosure	3,700,000		3,500,000
Modified loans, charged off	8,200,000
Financial Asset, 30 to 89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified, after 12 Months	500,000
90 DAYS OR MORE PAST DUE
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, Excluding Accrued Interest, Modified, after 12 Months	7,800,000
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, held-for-sale, not part of disposal group, after valuation allowance	0		0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 21,925,500,000		22,204,200,000
Personal | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on Residential real estate loan, lower limit	65%
Collateral required on Residential real estate loan, upper limit	80%
Loans and leases	$ 6,315,200,000		6,327,100,000
Personal | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products	10 years
Loans and leases	$ 229,900,000		$ 228,700,000
Percentage of total equity credit lines	98%		96%
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 25,417,100,000		$ 25,412,800,000

Loans (Credit Quality Indicator

Loans (Credit Quality Indicator At Amortized Cost By Origination Year) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	$ 9,388.8		$ 13,006.4
2023/2022	4,497.3		4,823.9
2022/2021	4,570.3		4,177.6
2021/2020	3,934.2		1,765.4
2020/2019	1,672.4		1,208.7
PRIOR	3,589.6		2,681.5
REVOLVING LOANS	18,959.3		19,233.5
REVOLVING LOANS CONVERTED TO TERM LOANS	730.7		720
TOTAL LOANS	47,342.6		47,617
2024/2023, Charge-offs	0		(2.1)
2023/2022, Charge-offs	(7.3)		(4.4)
2022/2021, Charge-offs	(3.7)		0
2021/2020, Charge-offs	0		0
2020/2019, Charge-offs	0		0
Prior, Charge-offs	(0.1)		(1)
REVOLVING LOANS, Charge-offs	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0		0
Charge-Offs	11.1	$ 4	7.5
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	8,111.7		10,601.2
2023/2022	3,180.9		3,008.8
2022/2021	2,840.7		2,212.4
2021/2020	2,144.3		536.3
2020/2019	472.9		590.8
PRIOR	1,322.2		899
REVOLVING LOANS	7,241.2		7,467.6
REVOLVING LOANS CONVERTED TO TERM LOANS	103.2		96.7
TOTAL LOANS	25,417.1		25,412.8
2024/2023, Charge-offs	0		(1.3)
2023/2022, Charge-offs	(7.3)		(4.4)
2022/2021, Charge-offs	(3.7)		0
2021/2020, Charge-offs	0		0
2020/2019, Charge-offs	0		0
Prior, Charge-offs	0		0
REVOLVING LOANS, Charge-offs	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0		0
Charge-Offs	11	4	5.7
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	91.3		1,259.1
2023/2022	1,173.5		1,395
2022/2021	1,291		1,458.6
2021/2020	1,400.4		228.8
2020/2019	191.4		257.8
PRIOR	759.6		590.3
REVOLVING LOANS	5,978		6,276.9
REVOLVING LOANS CONVERTED TO TERM LOANS	95.4		88.8
TOTAL LOANS	10,980.6		11,555.3
2024/2023, Charge-offs	0
2023/2022, Charge-offs	(7.3)
2022/2021, Charge-offs	(1.3)
2021/2020, Charge-offs	0
2020/2019, Charge-offs	0
Prior, Charge-offs	0
REVOLVING LOANS, Charge-offs	0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0
Charge-Offs	8.6
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	40.2		443.9
2023/2022	411.4		534.1
2022/2021	458.1		668.3
2021/2020	715.7		78.1
2020/2019	69.9		137.2
PRIOR	539.6		409.9
REVOLVING LOANS	4,735.9		4,909.8
REVOLVING LOANS CONVERTED TO TERM LOANS	15		15
TOTAL LOANS	6,985.8		7,196.3
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	51.1		801.4
2023/2022	757.9		790.9
2022/2021	757.4		729.5
2021/2020	627.1		138.7
2020/2019	117.6		120.5
PRIOR	218.3		178.7
REVOLVING LOANS	1,196.2		1,332.4
REVOLVING LOANS CONVERTED TO TERM LOANS	78.6		72
TOTAL LOANS	3,804.2		4,164.1
Commercial | Commercial and Institutional | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	0		13.8
2023/2022	4.2		70
2022/2021	75.5		60.8
2021/2020	57.6		12
2020/2019	3.9		0.1
PRIOR	1.7		1.7
REVOLVING LOANS	45.9		34.7
REVOLVING LOANS CONVERTED TO TERM LOANS	1.8		1.8
TOTAL LOANS	190.6		194.9
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	161.2		1,933.2
2023/2022	1,980.5		1,598.7
2022/2021	1,534.7		710.6
2021/2020	700.9		242.3
2020/2019	236.8		298.8
PRIOR	439.6		155.4
REVOLVING LOANS	271.5		187.3
REVOLVING LOANS CONVERTED TO TERM LOANS	7.8		7.9
TOTAL LOANS	5,333		5,134.2
2024/2023, Charge-offs	0		(0.7)
2023/2022, Charge-offs	0		(4.4)
2022/2021, Charge-offs	(2.4)		0
2021/2020, Charge-offs	0		0
2020/2019, Charge-offs	0		0
Prior, Charge-offs	0		0
REVOLVING LOANS, Charge-offs	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0		0
Charge-Offs	2.4		5.1
Commercial | Commercial Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	9.3		403.6
2023/2022	346.9		389.9
2022/2021	411.7		159.1
2021/2020	277.7		23.9
2020/2019	25.7		37.8
PRIOR	78.6		44.8
REVOLVING LOANS	67		51
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	1,216.9		1,110.1
Commercial | Commercial Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	151.9		1,513.5
2023/2022	1,617.5		1,208.8
2022/2021	1,087.7		521
2021/2020	392.9		218.4
2020/2019	208.6		252.8
PRIOR	340.6		96
REVOLVING LOANS	204.5		136.3
REVOLVING LOANS CONVERTED TO TERM LOANS	7.8		7.9
TOTAL LOANS	4,011.5		3,954.7
Commercial | Commercial Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	0		16.1
2023/2022	16.1		0
2022/2021	35.3		30.5
2021/2020	30.3		0
2020/2019	2.5		8.2
PRIOR	20.4		14.6
REVOLVING LOANS	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	104.6		69.4
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	1,128.4		1,464.1
2023/2022	26.9		15.1
2022/2021	15		43.2
2021/2020	43		65.2
2020/2019	44.7		34.2
PRIOR	123		153.3
REVOLVING LOANS	991.7		1,003.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	2,372.7		2,778.5
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	950.4		487.9
2023/2022	0		0
2022/2021	0		43.2
2021/2020	43		65.2
2020/2019	44.7		34.2
PRIOR	22.3		3.3
REVOLVING LOANS	933.5		760
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	1,993.9		1,393.8
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	176.9		974.7
2023/2022	26.9		0.8
2022/2021	0.8		0
2021/2020	0		0
2020/2019	0		0
PRIOR	100.7		150
REVOLVING LOANS	58.2		243.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	363.5		1,368.9
Commercial | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	1.1		1.5
2023/2022	0		14.3
2022/2021	14.2		0
2021/2020	0		0
2020/2019	0		0
PRIOR	0		0
REVOLVING LOANS	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	15.3		15.8
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	6,730.8		5,944.8
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
PRIOR	0		0
REVOLVING LOANS	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	6,730.8		5,944.8
2024/2023, Charge-offs	0		(0.6)
2023/2022, Charge-offs	0		0
2022/2021, Charge-offs	0		0
2021/2020, Charge-offs	0		0
2020/2019, Charge-offs	0		0
Prior, Charge-offs	0		0
REVOLVING LOANS, Charge-offs	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0		0
Charge-Offs	0		0.6
Commercial | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	3,865.8		4,313.2
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
PRIOR	0		0
REVOLVING LOANS	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	3,865.8		4,313.2
Commercial | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	2,865		1,631.6
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
PRIOR	0		0
REVOLVING LOANS	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	2,865		1,631.6
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	1,277.1		2,405.2
2023/2022	1,316.4		1,815.1
2022/2021	1,729.6		1,965.2
2021/2020	1,789.9		1,229.1
2020/2019	1,199.5		617.9
PRIOR	2,267.4		1,782.5
REVOLVING LOANS	11,718.1		11,765.9
REVOLVING LOANS CONVERTED TO TERM LOANS	627.5		623.3
TOTAL LOANS	21,925.5		22,204.2
2024/2023, Charge-offs	0		(0.8)
2023/2022, Charge-offs	0		0
2022/2021, Charge-offs	0		0
2021/2020, Charge-offs	0		0
2020/2019, Charge-offs	0		0
Prior, Charge-offs	(0.1)		(1)
REVOLVING LOANS, Charge-offs	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0		0
Charge-Offs	0.1	$ 0	1.8
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	50.7		818.4
2023/2022	813.2		629.3
2022/2021	559.3		707.4
2021/2020	569		168.4
2020/2019	156.4		167.5
PRIOR	286.3		197.7
REVOLVING LOANS	11,037.2		11,055.4
REVOLVING LOANS CONVERTED TO TERM LOANS	620.1		615.9
TOTAL LOANS	14,092.2		14,360
Personal | Private Client | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	28.9		504.7
2023/2022	472.7		140.8
2022/2021	109.5		52.3
2021/2020	49.5		67.5
2020/2019	60.1		8.7
PRIOR	96		134.7
REVOLVING LOANS	5,056.1		5,320.9
REVOLVING LOANS CONVERTED TO TERM LOANS	168.2		168.1
TOTAL LOANS	6,041		6,397.7
Personal | Private Client | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	21.8		290.1
2023/2022	324.3		488.2
2022/2021	449.6		655.1
2021/2020	519.5		100.9
2020/2019	96.3		158.8
PRIOR	190.3		44.7
REVOLVING LOANS	5,970.2		5,721.5
REVOLVING LOANS CONVERTED TO TERM LOANS	451.9		447.8
TOTAL LOANS	8,023.9		7,907.1
Personal | Private Client | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	0		23.6
2023/2022	16.2		0.3
2022/2021	0.2		0
2021/2020	0		0
2020/2019	0		0
PRIOR	0		18.3
REVOLVING LOANS	10.9		13
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	27.3		55.2
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	87.1		470.3
2023/2022	475.5		1,169.8
2022/2021	1,154.8		1,218
2021/2020	1,197		1,060.7
2020/2019	1,043.1		434
PRIOR	1,951.7		1,571.3
REVOLVING LOANS	406		403
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	6,315.2		6,327.1
2024/2023, Charge-offs	0		(0.8)
2023/2022, Charge-offs	0		0
2022/2021, Charge-offs	0		0
2021/2020, Charge-offs	0		0
2020/2019, Charge-offs	0		0
Prior, Charge-offs	(0.1)		(1)
REVOLVING LOANS, Charge-offs	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs	0		0
Charge-Offs	0.1		1.8
Personal | Residential Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	42.8		278.7
2023/2022	272.2		464
2022/2021	409.4		500.6
2021/2020	430.1		373.3
2020/2019	367.5		142.4
PRIOR	863.2		722.4
REVOLVING LOANS	230.9		219.8
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	2,616.1		2,701.2
Personal | Residential Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	44.3		191.6
2023/2022	203.3		694.9
2022/2021	738.1		717.4
2021/2020	766.8		686.7
2020/2019	675.2		290
PRIOR	1,042.9		805.3
REVOLVING LOANS	161.7		170.3
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	3,632.3		3,556.2
Personal | Residential Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	0		0
2023/2022	0		10.9
2022/2021	7.3		0
2021/2020	0.1		0.7
2020/2019	0.4		1.6
PRIOR	45.6		43.6
REVOLVING LOANS	13.4		12.9
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	66.8		69.7
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	8.4		28.2
2023/2022	27.7		16
2022/2021	15.5		39.8
2021/2020	23.9		0
2020/2019	0		16.4
PRIOR	29.4		13.5
REVOLVING LOANS	274.9		307.5
REVOLVING LOANS CONVERTED TO TERM LOANS	7.4		7.4
TOTAL LOANS	387.2		428.8
Personal | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	0.4		15.5
2023/2022	3.8		0
2022/2021	0		0.6
2021/2020	0.6		0
2020/2019	0		0
PRIOR	4.5		4.6
REVOLVING LOANS	43.9		71.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	53.2		92.1
Personal | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	0		12.7
2023/2022	23.9		16
2022/2021	15.5		39.2
2021/2020	23.3		0
2020/2019	0		16.4
PRIOR	24.9		8.9
REVOLVING LOANS	231		236.1
REVOLVING LOANS CONVERTED TO TERM LOANS	7.4		7.4
TOTAL LOANS	326		336.7
Personal | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	8		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
PRIOR	0		0
REVOLVING LOANS	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	8		0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	1,130.9		1,088.3
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
PRIOR	0		0
REVOLVING LOANS	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	1,130.9		1,088.3
Personal | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	636.3		461.7
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
PRIOR	0		0
REVOLVING LOANS	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	636.3		461.7
Personal | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2024/2023	494.6		626.6
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
PRIOR	0		0
REVOLVING LOANS	0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0
TOTAL LOANS	$ 494.6		$ 626.6

Loans (Delinquency Status) (Det

Loans (Delinquency Status) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	$ 47,305.6	$ 47,553.4
NONACCRUAL	37	63.6
TOTAL LOANS	47,342.6	47,617
NONACCRUAL WITH NO ALLOWANCE	35	49.4
Other Real Estate Owned	0	1.5
Total Nonaccrual Assets	37	65.1
CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	47,019.7	47,261.1
30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	226.8	239.5
60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	29.3	32.7
90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	29.8	20.1
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	25,403.8	25,396.5
NONACCRUAL	13.3	16.3
TOTAL LOANS	25,417.1	25,412.8
NONACCRUAL WITH NO ALLOWANCE	13.3	4.1
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	10,973	11,539
NONACCRUAL	7.6	16.3
TOTAL LOANS	10,980.6	11,555.3
NONACCRUAL WITH NO ALLOWANCE	7.6	4.1
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,327.3	5,134.2
NONACCRUAL	5.7	0
TOTAL LOANS	5,333	5,134.2
NONACCRUAL WITH NO ALLOWANCE	5.7	0
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,372.7	2,778.5
NONACCRUAL	0	0
TOTAL LOANS	2,372.7	2,778.5
NONACCRUAL WITH NO ALLOWANCE	0	0
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,730.8	5,944.8
NONACCRUAL	0	0
TOTAL LOANS	6,730.8	5,944.8
NONACCRUAL WITH NO ALLOWANCE	0	0
Commercial | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	25,331.7	25,221.6
Commercial | CURRENT | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	10,963	11,374.6
Commercial | CURRENT | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,265.2	5,123.7
Commercial | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,372.7	2,778.5
Commercial | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,730.8	5,944.8
Commercial | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	63.3	168.1
Commercial | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	7.3	163.7
Commercial | 30 – 59 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	56	4.4
Commercial | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
Commercial | 30 – 59 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
Commercial | 60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	6.8
Commercial | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0.7
Commercial | 60 – 89 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	6.1
Commercial | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
Commercial | 60 – 89 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
Commercial | 90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	8.8	0
Commercial | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2.7	0
Commercial | 90 DAYS OR MORE PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6.1	0
Commercial | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
Commercial | 90 DAYS OR MORE PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,901.8	22,156.9
NONACCRUAL	23.7	47.3
TOTAL LOANS	21,925.5	22,204.2
NONACCRUAL WITH NO ALLOWANCE	21.7	45.3
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	14,090.2	14,339.7
NONACCRUAL	2	20.3
TOTAL LOANS	14,092.2	14,360
NONACCRUAL WITH NO ALLOWANCE	0	18.3
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,293.5	6,300.1
NONACCRUAL	21.7	27
TOTAL LOANS	6,315.2	6,327.1
NONACCRUAL WITH NO ALLOWANCE	21.7	27
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	387.2	428.8
NONACCRUAL	0	0
TOTAL LOANS	387.2	428.8
NONACCRUAL WITH NO ALLOWANCE	0	0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	1,130.9	1,088.3
NONACCRUAL	0	0
TOTAL LOANS	1,130.9	1,088.3
NONACCRUAL WITH NO ALLOWANCE	0	0
Personal | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,688	22,039.5
Personal | CURRENT | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	13,941.1	14,240
Personal | CURRENT | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,261.2	6,283
Personal | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	354.8	428.2
Personal | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	1,130.9	1,088.3
Personal | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	163.5	71.4
Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	112.6	63.9
Personal | 30 – 59 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	18.5	7.5
Personal | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	32.4	0
Personal | 30 – 59 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
Personal | 60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	29.3	25.9
Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	18.5	24.8
Personal | 60 – 89 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	10.8	0.5
Personal | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0.6
Personal | 60 – 89 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
Personal | 90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21	20.1
Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	18	11
Personal | 90 DAYS OR MORE PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3	9.1
Personal | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
Personal | 90 DAYS OR MORE PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	$ 0	$ 0

Loans (Loan Modifications Made

Loans (Loan Modifications Made To Borrowers Experiencing Financial Difficulty) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 0.3	$ 2.9
% OF TOTAL SEGMENT	0%	0.05%
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 0	$ 0
% OF TOTAL SEGMENT	0%	0%
Personal
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 0.3	$ 2.9
% OF TOTAL SEGMENT	0%	0.05%
Personal | Residential Real Estate | Principal and/or interest deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 0	$ 2.9
% OF TOTAL SEGMENT	0%	0.05%
Financing receivable, modified, weighted average term increase from modification		180 days
Personal | Residential Real Estate | Extension of Term
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 0.1	$ 0
% OF TOTAL SEGMENT	0%	0%
Financing receivable, modified, weighted average term increase from modification	14 months
Personal | Private Client | Extension of Term
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 0.2	$ 0
% OF TOTAL SEGMENT	0%	0%
Financing receivable, modified, weighted average term increase from modification	22 months

Allowance for Credit Losses (Ch

Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
LOANS
Balance at Beginning of Period	$ 178.7	$ 144.3	$ 144.3
Charge-Offs	(11.1)	(4)	(7.5)
Recoveries	0.7	1.1
Net Recoveries (Charge-Offs)	(10.4)	(2.9)
Provision for Credit Losses	(5.9)	18.5
Balance at End of Period	162.4	159.9	178.7
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	26.9	38.5	38.5
Charge-Offs	0	0
Recoveries	0	0
Net Recoveries (Charge-Offs)	0	0
Provision for Credit Losses	(1.7)	(4.2)
Balance at End of Period	25.2	34.3	26.9
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	12.7	16	16
Charge-Offs	0	0
Recoveries	0	0
Net Recoveries (Charge-Offs)	0	0
Provision for Credit Losses	(0.3)	0
Balance at End of Period	12.4	16	12.7
OTHER FINANCIAL ASSETS
Balance at Beginning of Period	0.9	0.8	0.8
Charge-Offs	0	0
Recoveries	0	0
Net Recoveries (Charge-Offs)	0	0
Provision for Credit Losses	0.1	0.2
Balance at End of Period	1	1	0.9
TOTAL
Balance at Beginning of Period	219.2	199.6	199.6
Charge-Offs	(11.1)	(4)
Recoveries	0.7	1.1
Net Recoveries (Charge-Offs)	(10.4)	(2.9)
Provision for credit losses	(7.8)	14.5
Balance at End of Period	201	211.2	219.2
Corporate Debt
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	0.9	1.9	1.9
Provision for Credit Losses	(0.1)	0
Balance at End of Period	0.8	1.9	$ 0.9
TOTAL
Provision for credit losses	$ (0.7)	$ 0.5

Allowance for Credit Losses (Na

Allowance for Credit Losses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Receivables [Abstract]
Provision for (release of) credit losses	$ (7.8)	$ 14.5
Net charge-offs	$ 10.4	2.9
Time period used for projecting future conditions to estimate credit losses	2 years
Other financial assets, allowance for credit loss	$ 1	$ 1	$ 0.9	$ 0.8

Allowance for Credit Losses (_2

Allowance for Credit Losses (Changes in Allowance for Credit Losses Related to Loans) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
LOANS
Balance at Beginning of Period	$ 178.7	$ 144.3	$ 144.3
Charge-Offs	(11.1)	(4)	(7.5)
Recoveries	0.7	1.1
Net Recoveries (Charge-Offs)	(10.4)	(2.9)
Provision for Credit Losses	(5.9)	18.5
Balance at End of Period	162.4	159.9	178.7
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	26.9	38.5	38.5
Charge-Offs	0	0
Recoveries	0	0
Net Recoveries (Charge-Offs)	0	0
Provision for Credit Losses	(1.7)	(4.2)
Balance at End of Period	25.2	34.3	26.9
COMMERCIAL
LOANS
Balance at Beginning of Period	146.8	116.2	116.2
Charge-Offs	(11)	(4)	(5.7)
Recoveries	0	0
Net Recoveries (Charge-Offs)	(11)	(4)
Provision for Credit Losses	(4.1)	18.6
Balance at End of Period	131.7	130.8	146.8
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	24.9	36.3	36.3
Charge-Offs	0	0
Recoveries	0	0
Net Recoveries (Charge-Offs)	0	0
Provision for Credit Losses	(2.4)	(5)
Balance at End of Period	22.5	31.3	24.9
PERSONAL
LOANS
Balance at Beginning of Period	31.9	28.1	28.1
Charge-Offs	(0.1)	0	(1.8)
Recoveries	0.7	1.1
Net Recoveries (Charge-Offs)	0.6	1.1
Provision for Credit Losses	(1.8)	(0.1)
Balance at End of Period	30.7	29.1	31.9
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	2	2.2	2.2
Charge-Offs	0	0
Recoveries	0	0
Net Recoveries (Charge-Offs)	0	0
Provision for Credit Losses	0.7	0.8
Balance at End of Period	$ 2.7	$ 3	$ 2

Allowance for Credit Losses (Re

Allowance for Credit Losses (Recorded Investments in Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Loans
Evaluated on an Individual Basis	$ 53.2	$ 96.3
Evaluated on a Collective Basis	47,289.4	47,520.7
TOTAL LOANS	47,342.6	47,617
Allowance for Credit Losses on Loans
Evaluated on an Individual Basis	2.5	13.4
Evaluated on a Collective Basis	159.9	165.3
Allowance Assigned to Loans	162.4	178.7	$ 159.9	$ 144.3
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on a Collective Basis	25.2	26.9
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	25.2	26.9	34.3	38.5
Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit	187.6	205.6
COMMERCIAL
Loans
Evaluated on an Individual Basis	14.5	33.7
Evaluated on a Collective Basis	25,402.6	25,379.1
TOTAL LOANS	25,417.1	25,412.8
Allowance for Credit Losses on Loans
Evaluated on an Individual Basis	0.5	11.4
Evaluated on a Collective Basis	131.2	135.4
Allowance Assigned to Loans	131.7	146.8	130.8	116.2
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on a Collective Basis	22.5	24.9
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	22.5	24.9	31.3	36.3
Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit	154.2	171.7
PERSONAL
Loans
Evaluated on an Individual Basis	38.7	62.6
Evaluated on a Collective Basis	21,886.8	22,141.6
TOTAL LOANS	21,925.5	22,204.2
Allowance for Credit Losses on Loans
Evaluated on an Individual Basis	2	2
Evaluated on a Collective Basis	28.7	29.9
Allowance Assigned to Loans	30.7	31.9	29.1	28.1
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on a Collective Basis	2.7	2
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	2.7	2	$ 3	$ 2.2
Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit	$ 33.4	$ 33.9

Allowance for Credit Losses (_3

Allowance for Credit Losses (Changes in The Allowance for Credit Losses Related to Debt Securities Held to Maturity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	$ 12.7	$ 16
Provision for Credit Losses	(0.3)	0
Balance at End of Period	12.4	16
CORPORATE DEBT
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	0.9	1.9
Provision for Credit Losses	(0.1)	0
Balance at End of Period	0.8	1.9
NON-U.S. GOVERNMENT
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	3.5	3.6
Provision for Credit Losses	0	0.3
Balance at End of Period	3.5	3.9
SUB-SOVEREIGN, SUPRANATIONAL, AND NON-U.S. AGENCY BONDS
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	2.2	4
Provision for Credit Losses	(0.1)	0.1
Balance at End of Period	2.1	4.1
OBLIGATIONS OF STATES AND POICITAL SUBDIVISIONS
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	1.2	1.5
Provision for Credit Losses	(0.1)	(0.2)
Balance at End of Period	1.1	1.3
COVERED BONDS
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	0.1	0.1
Provision for Credit Losses	0	0
Balance at End of Period	0.1	0.1
OTHER
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	4.8	4.9
Provision for Credit Losses	0	(0.2)
Balance at End of Period	$ 4.8	$ 4.7

Allowance for Credit Losses (Ac

Allowance for Credit Losses (Accrued Interest) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Receivables [Abstract]
Loans	$ 253	$ 241.7
Debt Securities
Held to Maturity	69.8	72
Available for Sale	175	129.2
Other Financial Assets	110.3	86
Total	$ 608.1	$ 528.9

Pledged Assets, Collateral an_3

Pledged Assets, Collateral and Restricted Assets (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Financial Instruments Owned and Pledged as Collateral [Line Items]
Cash, held in foreign currency	$ 818,900,000		$ 722,200,000
Restricted cash	563,400,000		575,200,000
Average deposits maintained to meet Federal Reserve Bank reserve requirements	0	$ 0
Debt Securities And Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 1,400,000,000		$ 1,100,000,000

Pledged Assets, Collateral an_4

Pledged Assets, Collateral and Restricted Assets (Type of Pledged Assets) (Details) - Collateral that may be repledged or sold - USD ($) $ in Billions	Mar. 31, 2024	Dec. 31, 2023
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 41.4	$ 43.3
Debt Securities [Member]
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	30.8	33
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 10.6	$ 10.3

Pledged Assets, Collateral an_5

Pledged Assets, Collateral and Restricted Assets (Accepted Collateral) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Collateral Accepted	$ 66,331.5	$ 62,780
Fair value of securities received as collateral that have been resold or repledged	65,700	62,000
Reverse repurchase agreements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	66,327.9	62,767.8
Reverse repurchase agreements	0	0
Derivative contracts
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 3.6	$ 12.2

Goodwill and Other Intangible_2

Goodwill and Other Intangibles (Goodwill by Reporting Segment) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($)
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 702.3
Foreign Exchange Rates	(4.8)
Goodwill, Ending Balance	697.5
ASSET SERVICING
Goodwill [Roll Forward]
Goodwill, Beginning Balance	621.9
Foreign Exchange Rates	(4.8)
Goodwill, Ending Balance	617.1
WEALTH MANAGEMENT
Goodwill [Roll Forward]
Goodwill, Beginning Balance	80.4
Foreign Exchange Rates	0
Goodwill, Ending Balance	$ 80.4

Goodwill and Other Intangible_3

Goodwill and Other Intangibles (Other Intangible Assets and Capitalized Software) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 130.9	$ 135
Less: Accumulated Amortization	63.9	63.4
Net Book Value	67	71.6
Computer Software
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,905.3	3,781.7
Less: Accumulated Amortization	1,893.9	1,754.2
Net Book Value	$ 2,011.4	$ 2,027.5

Goodwill and Other Intangible_4

Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets amortization	$ 2.3	$ 2.3
Estimated future amortization expense for 2024	6.9
Estimated future amortization expense for 2025	8.6
Estimated future amortization expense for 2026	8.3
Estimated future amortization expense for 2027	8
Estimated future amortization expense for 2028	7.4
Computer Software
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets amortization	$ 140.4	$ 121.3

Reporting Segments (Results of

Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($) segment	Mar. 31, 2023 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment	2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,142.9	$ 1,063.6
Foreign Exchange Trading Income	57	53
Other Noninterest Income (Loss)	(81.2)	96.8
Total Noninterest Income	1,118.7	1,213.4
Net Interest Income	528.1	531.2
Revenue	1,646.8	1,744.6
Provision for Credit Losses	(8.5)	15
Noninterest Expense	1,364.7	1,285.6
Income before Income Taxes	290.6	444
Provision for Income Taxes	75.9	109.4
Net Income	$ 214.7	$ 334.6
Percentage of Consolidated Net Income	100%	100%
Average Assets	$ 145,118.3	$ 148,059.9
RECONCILING ITEMS
Noninterest Income
Trust, Investment and Other Servicing Fees	0	0
Foreign Exchange Trading Income	0	0
Other Noninterest Income (Loss)	0	0
Total Noninterest Income	0	0
Net Interest Income	(7.3)	(13.2)
Revenue	(7.3)	(13.2)
Provision for Credit Losses	0	0
Noninterest Expense	0	0
Income before Income Taxes	(7.3)	(13.2)
Provision for Income Taxes	(7.3)	(13.2)
Net Income	0	0
OTHER
Noninterest Income
Trust, Investment and Other Servicing Fees	0	0
Foreign Exchange Trading Income	0	0
Other Noninterest Income (Loss)	(190.5)	(0.7)
Total Noninterest Income	(190.5)	(0.7)
Net Interest Income	0	0
Revenue	(190.5)	(0.7)
Provision for Credit Losses	(1)	0
Noninterest Expense	20.3	15.4
Income before Income Taxes	(209.8)	(16.1)
Provision for Income Taxes	(54.8)	(4)
Net Income	(155)	$ (12.1)
Percentage of Consolidated Net Income		(4.00%)
Average Assets	0	$ 0
ASSET SERVICING | Scenario, Adjustment
Noninterest Income
Net Interest Income	(31)
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	639.6	603
Foreign Exchange Trading Income	59.9	54.9
Other Noninterest Income (Loss)	70.8	63.2
Total Noninterest Income	770.3	721.1
Net Interest Income	293.8	312.1
Revenue	1,064.1	1,033.2
Provision for Credit Losses	(5.8)	(2.9)
Noninterest Expense	852.7	801
Income before Income Taxes	217.2	235.1
Provision for Income Taxes	56.6	60.5
Net Income	160.6	$ 174.6
Percentage of Consolidated Net Income		52%
Average Assets	106,955	$ 111,215.3
WEALTH MANAGEMENT | Scenario, Adjustment
Noninterest Income
Net Interest Income	31
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	503.3	460.6
Foreign Exchange Trading Income	(2.9)	(1.9)
Other Noninterest Income (Loss)	38.5	34.3
Total Noninterest Income	538.9	493
Net Interest Income	241.6	232.3
Revenue	780.5	725.3
Provision for Credit Losses	(1.7)	17.9
Noninterest Expense	491.7	469.2
Income before Income Taxes	290.5	238.2
Provision for Income Taxes	81.4	66.1
Net Income	209.1	$ 172.1
Percentage of Consolidated Net Income		52%
Average Assets	$ 38,163.3	$ 36,844.6

Stockholders' Equity (Narrative

Stockholders' Equity (Narrative) (Details) - USD ($)		3 Months Ended
	Jan. 17, 2024	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Oct. 31, 2021
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		10,000,000		10,000,000
Stockholders' equity		$ 12,101,800,000	$ 11,587,800,000	$ 11,897,900,000	$ 11,259,500,000
Common stock dividends (in usd per share)		$ 0.75	$ 0.75
Stock repurchase program, number of shares authorized to be repurchased (in shares)						25,000,000
Stock repurchase, shares (in shares)		1,647,526	1,050,227
Stock repurchase, aggregate cost		$ 132,000,000	$ 100,900,000
Share-based payment arrangement, shares withheld for tax withholding obligation (in shares)		373,623	326,811
Average price paid per share for common stock repurchased (in usd per share)		$ 80.11	$ 96.04
Preferred Stock
Class of Stock [Line Items]
Stockholders' equity		$ 884,900,000	$ 884,900,000	$ 884,900,000	$ 884,900,000
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		5,000		5,000
Preferred stock, without par value (in dollars per share)		$ 0
Preferred stock, liquidation preference		$ 100,000
Depository shares, liquidation preference per share (in dollars per share)		$ 1,000
Preferred stock, annual dividend rate		4.60%
Preferred stock, dividend payment rate, variable rate		3.202%
Common stock dividends (in usd per share)	$ 2,300
Series D Preferred Stock | Preferred Stock
Class of Stock [Line Items]
Stockholders' equity		$ 493,500,000		$ 493,500,000
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		16,000		16,000
Percentage of ownership interest per each depository shares		0.10%
Preferred stock, without par value (in dollars per share)		$ 0
Preferred stock, liquidation preference		$ 25,000
Depository shares, liquidation preference per share (in dollars per share)		$ 25
Preferred stock, annual dividend rate		4.70%
Common stock dividends (in usd per share)	$ 293.75
Series E Preferred Stock | Preferred Stock
Class of Stock [Line Items]
Stockholders' equity		$ 391,400,000		$ 391,400,000
Series D Preferred Stock, Depositary Shares
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		500,000
Preferred stock, shares issued (in shares)		500,000
Percentage of ownership interest per each depository shares		1%
Series E Preferred Stock Depositary Shares
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		16,000,000
Preferred stock, shares issued (in shares)		16,000,000

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) (Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 11,897.9	$ 11,259.5
Net Change	220.3	203
Ending balance	12,101.8	11,587.8
TOTAL
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(1,137.9)	(1,569.2)
Net Change	220.3	203
Ending balance	(917.6)	(1,366.2)
NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(923.9)	(1,367.6)
Net Change	213.4	180.2
Ending balance	(710.5)	(1,187.4)
NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	0.8	1.2
Net Change	(0.7)	(0.1)
Ending balance	0.1	1.1
NET FOREIGN CURRENCY ADJUSTMENT
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	203.6	164.6
Net Change	4.6	22.7
Ending balance	208.2	187.3
NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(418.4)	(367.4)
Net Change	3	0.2
Ending balance	$ (415.4)	$ (367.2)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) (Details of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
PRE-TAX
Net Change	$ 312.5	$ 259
TAX
Net Change	(92.2)	(56)
AFTER TAX
Net Change	220.3	203
Unrealized Gains (Losses) on Available for Sale Debt Securities
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	73.2	229.3
Net Change	287	244.3
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(19.4)	(60.3)
Net Change	(73.6)	(64.1)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	53.8	169
Net Change	213.4	180.2
Interest Income on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	24.4	21.9
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(6.2)	(5.5)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	18.2	16.4
Net Losses on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	189.4	(6.9)
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(48)	1.7
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	141.4	(5.2)
Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(5.5)	(0.6)
Net Change	(1)	(0.1)
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	1.4	0.1
Net Change	0.3	0
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(4.1)	(0.5)
Net Change	(0.7)	(0.1)
Foreign Currency Adjustments
PRE-TAX
Net Change	22.2	14.3
TAX
Net Change	(17.6)	8.4
AFTER TAX
Net Change	4.6	22.7
Foreign Currency Translation Adjustments
PRE-TAX
Net Change	(58.5)	46.8
TAX
Net Change	2.9	0.2
AFTER TAX
Net Change	(55.6)	47
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
PRE-TAX
Net Change	(0.6)	0
TAX
Net Change	0.1	0
AFTER TAX
Net Change	(0.5)	0
Net Investment Hedge Gains (Losses)
PRE-TAX
Net Change	81.3	(32.5)
TAX
Net Change	(20.6)	8.2
AFTER TAX
Net Change	60.7	(24.3)
Pension and Other Postretirement Benefit Adjustments
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	1.1	(1.1)
Net Change	4.3	0.5
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(0.5)	0.1
Net Change	(1.3)	(0.3)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	0.6	(1)
Net Change	3	0.2
Amortization of Net Actuarial Loss
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	3.2	1.6
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.8)	(0.4)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	2.4	1.2
Foreign Exchange Contracts | Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	4.5	0.5
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(1.1)	(0.1)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	$ 3.4	$ 0.4

Net Income Per Common Share (Ne

Net Income Per Common Share (Net Income Per Common Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Basic Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	204,628,796	208,186,841
Net Income	$ 214.7	$ 334.6
Less: Dividends on Preferred Stock	16.2	16.2
Net Income Applicable to Common Stock	198.5	318.4
Less: Earnings Allocated to Participating Securities	2.4	3.2
Earnings Allocated to Common Shares Outstanding	$ 196.1	$ 315.2
Basic Net Income Per Common Share (in dollars per share)	$ 0.96	$ 1.51
Diluted Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	204,628,796	208,186,841
Plus: Dilutive Effect of Share-based Compensation (in shares)	506,049	543,548
Average Common and Potential Common Shares (in shares)	205,134,845	208,730,389
Earnings Allocated to Common and Potential Common Shares	$ 196.1	$ 315.2
Diluted Net Income Per Common Share (in dollars per share)	$ 0.96	$ 1.51
Common stock equivalents not included in the computation of diluted earnings per share because their inclusion would have been antidilutive (in shares)	0	0

Revenue from Contracts with C_3

Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,142.9	$ 1,063.6
Foreign Exchange Trading Income	57	53
Treasury Management Fees	9.3	8.4
Security Commissions and Trading Income	37.9	34.7
Other Operating Income	61	46.8
Investment Security Gains (Losses), net	(189.4)	6.9
Total Other Noninterest Income	(24.2)	149.8
Total Noninterest Income	1,118.7	1,213.4
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	467.4	441.6
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	593.9	540.5
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	18.6	19.1
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 63	$ 62.4

Revenue from Contracts with C_4

Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,142.9	$ 1,063.6
Security commissions and trading income	37.9	34.7
Other operating income	61	46.8
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	33.7	29.9
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 9.3	$ 9.1

Revenue from Contracts with C_5

Revenue from Contracts with Clients (Contract Receivables) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Total Client Receivables	$ 997.1	$ 928.4
Trust Fees Receivable, net
Disaggregation of Revenue [Line Items]
Total Client Receivables	949.4	863.5
Contract with customer, asset, allowance for credit loss	14.8	15.9
Other
Disaggregation of Revenue [Line Items]
Total Client Receivables	$ 47.7	$ 64.9

Net Interest Income (Net Intere

Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Interest Income
Federal Reserve and Other Central Bank Deposits	$ 459.7	$ 377
Interest-Bearing Due from and Deposits with Banks	34.6	28.2
Federal Funds Sold	0	0.2
Securities Purchased under Agreements to Resell	823.9	125.9
Securities — Taxable	445.3	337.8
Securities - Non-Taxable	0.3	0.3
Loans	653.6	578.2
Other Interest-Earning Assets	28.2	7.8
Total Interest Income	2,445.6	1,455.4
Interest Expense
Deposits	881.7	564.6
Federal Funds Purchased	33.6	40.1
Securities Sold Under Agreements to Repurchase	813.9	116.1
Other Borrowings	88.6	135
Senior Notes	44.1	39.2
Long-Term Debt	55.6	29.2
Total Interest Expense	1,917.5	924.2
Net Interest Income	$ 528.1	$ 531.2

Other Operating Income - (Detai

Other Operating Income - (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Components of Other Operating Income [Line Items]
Other operating income	$ 61	$ 46.8
Loan Service Fees
Components of Other Operating Income [Line Items]
Other operating income	15.7	18.7
Banking Service Fees
Components of Other Operating Income [Line Items]
Other operating income	13.3	12.2
Bank Owned Life Insurance
Components of Other Operating Income [Line Items]
Other operating income	20.6	16.7
Other Income
Components of Other Operating Income [Line Items]
Other operating income	$ 11.4	$ (0.8)

Other Operating Expense (Detail

Other Operating Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Other Income and Expenses [Abstract]
Business Promotion	$ 16.7	$ 16.2
Staff Related	14.2	7.8
FDIC Insurance Premiums(1)	18.7	6.2
Charitable Contributions	2	3.2
Other Expenses	48.8	52.2
Total Other Operating Expense	100.4	$ 85.6
FDIC, special assessment	$ 12.5

Pension ((Benefit)) (Details)

Pension ((Benefit)) (Details) - Pension Plan - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
U.S. Plan | Qualified Plan
Defined Benefit Plan, Net Periodic Benefit Cost
Service Cost	$ 13,400,000	$ 11,500,000
Interest Cost	13,900,000	13,500,000
Expected Return on Plan Assets	(28,900,000)	(25,300,000)
Amortization
Actuarial Loss (Gain)	1,900,000	400,000
Total Pension (Benefit) Expense	300,000	100,000
Contribution to pension plan	200,000,000	0
U.S. Plan | Non-Qualified Plan
Defined Benefit Plan, Net Periodic Benefit Cost
Service Cost	1,200,000	1,200,000
Interest Cost	1,200,000	1,300,000
Amortization
Actuarial Loss (Gain)	1,300,000	1,300,000
Total Pension (Benefit) Expense	3,700,000	3,800,000
Contribution to pension plan	8,000,000	16,500,000
Non-U.S. Plan
Defined Benefit Plan, Net Periodic Benefit Cost
Service Cost	500,000	300,000
Interest Cost	1,100,000	1,200,000
Expected Return on Plan Assets	(1,600,000)	(1,500,000)
Amortization
Actuarial Loss (Gain)	0	(100,000)
Total Pension (Benefit) Expense	$ 0	$ (100,000)

Share-Based Compensation Plan_2

Share-Based Compensation Plans - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-based Payment Arrangement, Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares)	1,086,910	1,029,713
Grant date fair value	$ 86	$ 95.9
Share-based payment arrangement, nonvested award, cost not yet recognized, amount	$ 28.8	$ 31.4
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares)	262,557	219,314
Grant date fair value	$ 21	$ 20.6
Share-based payment arrangement, nonvested award, cost not yet recognized, amount	12.8	14.2
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, nonvested award, cost not yet recognized, amount	$ 4.5	$ 4.2

Share-Based Compensation Plan_3

Share-Based Compensation Plans (Compensation Expense for Share-Based Arrangements and Tax Impacts) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	$ 66.4	$ 64.4
Tax Benefits Recognized	16.8	16.2
Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	49.4	50.3
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	$ 17	$ 14.1

Variable Interest Entities (Sum

Variable Interest Entities (Summary) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Variable Interest Entity [Line Items]
Assets	$ 156,111	$ 150,783.1
Liabilities	144,009.2	138,885.2
Other Assets
Variable Interest Entity [Line Items]
Investment Carrying Amount	866.4	889.1
Other Assets | Affordable Housing
Variable Interest Entity [Line Items]
Investment Carrying Amount	603.3	622.8
Other Assets | New Markets
Variable Interest Entity [Line Items]
Investment Carrying Amount	263.1	266.3
Other Liabilities
Variable Interest Entity [Line Items]
Unfunded Commitments	163.3	178.8
Other Liabilities | Affordable Housing
Variable Interest Entity [Line Items]
Unfunded Commitments	163.3	178.8
Other Liabilities | New Markets
Variable Interest Entity [Line Items]
Unfunded Commitments	0	0
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	835.7	857
Liabilities	$ 156.6	$ 172

Variable Interest Entities (Inc

Variable Interest Entities (Income Tax Credits and Other Tax Benefits and Amortization Expense) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Variable Interest Entity [Line Items]
Income Tax Credits and Other Income Tax Benefits	$ 26.7	$ 28.3
Amortization Expense	23.9	24.5
Affordable Housing
Variable Interest Entity [Line Items]
Income Tax Credits and Other Income Tax Benefits	21.7	22.4
Amortization Expense	19.5	19.8
New Markets
Variable Interest Entity [Line Items]
Income Tax Credits and Other Income Tax Benefits	5	5.9
Amortization Expense	$ 4.4	$ 4.7

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Contractual obligation to provide financial support	$ 0
Unfunded commitments	0
Investment company, voluntary fee waived	$ 2,300,000	$ 2,000,000

Commitments and Contingent Li_3

Commitments and Contingent Liabilities (Summary of Off-Balance Sheet Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 255,670.7	$ 265,837.5
OVER ONE YEAR	19,284.4	19,549.9
TOTAL	274,955.1	285,387.4
Undrawn Commitments
Loss Contingencies [Line Items]
Commitments, participated to others	259.1	222.2
Securities Lent with Indemnification
Loss Contingencies [Line Items]
ONE YEAR AND LESS	138,278.1	140,539.1
OVER ONE YEAR	0	0
TOTAL	138,278.1	140,539.1
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	41	39.1
Standby Letter of Credit and Financial Guarantee
Loss Contingencies [Line Items]
Guarantor obligations, current carrying value	89,300	84,600
Undrawn Commitments
Loss Contingencies [Line Items]
ONE YEAR AND LESS	10,322.2	11,849.5
OVER ONE YEAR	18,957.1	18,909.6
TOTAL	29,279.3	30,759.1
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	90,610.8	85,752
OVER ONE YEAR	327.2	639
TOTAL	90,938	86,391
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	17.2	29.2
OVER ONE YEAR	0.1	1.3
TOTAL	17.3	30.5
Reverse repurchase agreements
Loss Contingencies [Line Items]
ONE YEAR AND LESS	16,442.4	27,667.7
OVER ONE YEAR	0	0
TOTAL	$ 16,442.4	$ 27,667.7

Commitments and Contingent Li_4

Commitments and Contingent Liabilities (Narrative) (Details) $ / shares in Units, shares in Millions					1 Months Ended		3 Months Ended		12 Months Ended
	Apr. 08, 2024 exchangeOffer	Mar. 28, 2024 USD ($) $ / shares	Mar. 05, 2024 EUR (€)	Sep. 13, 2023	Jun. 30, 2016 USD ($) shares	Jun. 30, 2015 USD ($) shares	Mar. 31, 2024 USD ($) shares	Dec. 31, 2023 USD ($) shares	Dec. 31, 2015 trust
Loss Contingencies [Line Items]
Minimum securities lending related collateral percentage							100%
Commitments and letters of credit							$ 274,955,100,000	$ 285,387,400,000
Resell agreements, period end amounts excluding effects of agreements reported net by counterparty							16,400,000,000	27,700,000,000
Repurchase agreement counterparty, amount at risk							0	$ 0
FDIC, special assessment							12,500,000
Loss contingency accrual							0
Escrow deposit							$ 2,800,000,000
Common stock, convertible, conversion price							1.5875
Visa Class A Common Stock | Visa
Loss Contingencies [Line Items]
Share price (in usd) | $ / shares		$ 279.08
Visa Class A Common Stock | Subsequent Event
Loss Contingencies [Line Items]
Potential exchange offer program, number of exchange offers | exchangeOffer	3
Potential exchange offer program, length of time between exchanges	12 months
Potential exchange offer program, claim reduction percentage	50%
Visa Class A Common Stock | Period One
Loss Contingencies [Line Items]
Potential exchange offer program, exchange ratio				0.3333
Visa Class A Common Stock | Period One | Subsequent Event
Loss Contingencies [Line Items]
Potential exchange offer program, conversion period	45 days
Visa Class A Common Stock | Period Two
Loss Contingencies [Line Items]
Potential exchange offer program, exchange ratio				0.6666
Visa Class A Common Stock | Period Two | Subsequent Event
Loss Contingencies [Line Items]
Potential exchange offer program, conversion period	90 days
Visa Class A Common Stock | Period Three | Subsequent Event
Loss Contingencies [Line Items]
Potential exchange offer program, conversion period	90 days
Visa Class B
Loss Contingencies [Line Items]
Visa redemption gain					$ 123,100,000	$ 99,900,000
Shares issued (in shares) | shares					1.1	1
Common stock shares held (in shares) | shares							4.1	4.1
Remaining Visa shares held by Northern Trust, original cost basis							$ 0	$ 0
Conversion of stock, amount converted		$ 1,800,000,000
Northern Trust Fiduciary Services (Guernsey) Limited | Subsidiaries
Loss Contingencies [Line Items]
Number of administrated trusts serving as trustee on | trust									2
Lower Limit
Loss Contingencies [Line Items]
Possible loss in future periods in excess of accrual							0
Upper Limit
Loss Contingencies [Line Items]
Possible loss in future periods in excess of accrual							25,000,000
Indemnification Agreement
Loss Contingencies [Line Items]
Credit loss liability							0	0
FDIC Special Assessment
Loss Contingencies [Line Items]
FDIC, special assessment								$ 84,600,000
Possible loss in future periods in excess of accrual							$ 12,500,000
Northern Trust Fiduciary Services (Guernsey) Limited
Loss Contingencies [Line Items]
Litigation settlement, amount awarded to other party | €			€ 187,500

Derivative Financial Instrume_3

Derivative Financial Instruments (Notional and Fair Values of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Derivative [Line Items]
NOTIONAL VALUE	$ 347,592.9	$ 340,383.3
FAIR VALUE, ASSET	1,327.3	3,307.8
Total Gross Derivatives, asset	1,761.1	3,568.2
Less: Netting	914.2	3,126.7
Derivative Assets	846.9	441.5
FAIR VALUE, LIABILITY	1,630.2	2,806.3
Derivative Liabilities	1,817	3,649.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,070.1	2,205.4
Derivative Liabilities	746.9	1,444.4
Derivatives Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	13,718	12,573.7
FAIR VALUE, ASSET	207.6	123
FAIR VALUE, LIABILITY	420.9	145.1
Fair Value Hedges | Derivatives Designated as Hedging under GAAP | Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	9,466.4	7,042.7
FAIR VALUE, ASSET	182.4	94.7
FAIR VALUE, LIABILITY	420.1	71
Fair Value Hedges | Derivatives Not Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	333,874.9	327,809.6
FAIR VALUE, ASSET	1,553.5	3,445.2
FAIR VALUE, LIABILITY	1,396.1	3,504.7
Fair Value Hedges | Non-Designated Risk Management Derivatives
Derivative [Line Items]
NOTIONAL VALUE	930.4	888.6
FAIR VALUE, ASSET	0	0
FAIR VALUE, LIABILITY	21	25.5
Fair Value Hedges | Non-Designated Risk Management Derivatives | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	0	20.7
FAIR VALUE, ASSET	0	0
FAIR VALUE, LIABILITY	0	0.1
Fair Value Hedges | Non-Designated Risk Management Derivatives | Other Financial Derivatives
Derivative [Line Items]
NOTIONAL VALUE	930.4	867.9
FAIR VALUE, ASSET	0	0
FAIR VALUE, LIABILITY	21	25.4
Fair Value Hedges | Client-Related and Trading Derivatives
Derivative [Line Items]
NOTIONAL VALUE	332,944.5	326,921
FAIR VALUE, ASSET	1,553.5	3,445.2
FAIR VALUE, LIABILITY	1,375.1	3,479.2
Fair Value Hedges | Client-Related and Trading Derivatives | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	317,051.6	313,336.9
FAIR VALUE, ASSET	1,331.9	3,238.4
FAIR VALUE, LIABILITY	1,317.3	3,181
Fair Value Hedges | Client-Related and Trading Derivatives | Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	15,892.9	13,584.1
FAIR VALUE, ASSET	221.6	206.8
FAIR VALUE, LIABILITY	57.8	298.2
Cash Flow Hedges | Derivatives Designated as Hedging under GAAP | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	164.9	1,453.6
FAIR VALUE, ASSET	4	15
FAIR VALUE, LIABILITY	0	42.2
Net Investment Hedges | Derivatives Designated as Hedging under GAAP | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	4,086.7	4,077.4
FAIR VALUE, ASSET	21.2	13.3
FAIR VALUE, LIABILITY	$ 0.8	$ 31.9

Derivative Financial Instrume_4

Derivative Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Derivative [Line Items]
Gains or losses reclassified into earnings	$ 0	$ 0
Maximum length of time over which exposure was being hedged	1 month
Net investment gains (losses) recognized in AOCI	$ 81,300,000	$ (32,500,000)
Cash Flow Hedges, Foreign-Currency-Denominated Debt Securities
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges	$ 4,000,000

Derivative Financial Instrume_5

Derivative Financial Instruments (Location and Amount of Fair Value And Cash Flow Hedge Derivative Gains And Losses Recorded In Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 2,445.6	$ 1,455.4
Interest Expense	1,917.5	924.2
Other Operating Income	61	46.8
INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	22.3	12.3
Gains (Losses) on cash flow hedges recognized on	5.5	0
INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	(19.9)	(18.4)
Gains (Losses) on cash flow hedges recognized on	0	0
OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	0	0
Gains (Losses) on cash flow hedges recognized on	0	0.6
Interest Rate Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	123	(18.5)
Recognized on hedged items	(123)	18.5
Amounts related to interest settlements on derivatives	22.3	12.3
Interest Rate Contracts | INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(30.1)	49.1
Recognized on hedged items	30.1	(49.1)
Amounts related to interest settlements on derivatives	(19.9)	(18.4)
Interest Rate Contracts | OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	0	0
Recognized on hedged items	0	0
Amounts related to interest settlements on derivatives	0	0
Foreign Exchange Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on cash flow hedges recognized on	5.5	0
Foreign Exchange Contracts | INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on cash flow hedges recognized on	0	0
Foreign Exchange Contracts | OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on cash flow hedges recognized on	$ 0	$ 0.6

Derivative Financial Instrume_6

Derivative Financial Instruments (Hedged Items In Fair Value Hedges) (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Carrying value of the hedged items, available for sale debt securities	$ 7,319,000,000	$ 5,048,800,000
Cumulative hedge accounting basis adjustment, available for sale debt securities	(45,500,000)	77,500,000
Carrying value of the hedged items, senior notes and long-term subordinated debt	2,469,900,000	2,495,900,000
Cumulative hedge accounting basis adjustment, senior notes and long-term subordinated debt	(274,800,000)	(248,700,000)
Hedged asset fair value hedge discontinued cumulative increase decrease	2,100,000	2,200,000
Hedged liability fair value hedge discontinued cumulative increase decrease	$ 25,600,000	$ 29,600,000

Derivative Financial Instrume_7

Derivative Financial Instruments (Location and Amount of Gains and Losses Recorded in Income for Derivatives Not Designated As Hedging Under GAAP) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Derivatives Not Designated as Hedging under GAAP
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 56.8	$ 47.4
Non-Designated Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	(1.4)	(8.1)
Non-Designated Risk Management Derivatives | Foreign Exchange Contracts
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ (0.2)	$ 0.7
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Operating Income	Other Operating Income
Non-Designated Risk Management Derivatives | Other Financial Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ (1.2)	$ (8.8)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Operating Income	Other Operating Income
Client-Related and Trading Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 58.2	$ 55.5
Client-Related and Trading Derivatives | Foreign Exchange Contracts
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 57	$ 53
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Foreign Exchange Trading Income	Foreign Exchange Trading Income
Client-Related and Trading Derivatives | Interest Rate Contracts
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 1.2	$ 2.5
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Security Commissions and Trading Income	Security Commissions and Trading Income

Securities Sold Under Agreeme_3

Securities Sold Under Agreements to Repurchase (Repurchase Agreements Accounted for as Secured Borrowings) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Securities Sold Under Agreements to Repurchase	$ 511.4	$ 784.7
OVERNIGHT AND CONTINUOUS
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	511.4	784.7
OVERNIGHT AND CONTINUOUS | U.S. Treasury and Agency Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	$ 511.4	$ 784.7

Offsetting of Assets and Liab_3

Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 1,327.3	$ 3,307.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	914.2	3,126.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	413.1	181.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	3.6	12.2
NET AMOUNT	409.5	168.9
Total Derivatives Not Subject to a Master Netting Arrangement
Total Derivatives Not Subject to a Master Netting Arrangement	433.8	260.4
Total Derivatives
GROSS RECOGNIZED ASSETS	1,761.1	3,568.2
Derivative Assets	846.9	441.5
NET AMOUNT	843.3	429.3
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	66,364.6	62,860.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	65,864.5	62,075.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	500.1	784.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	500.1	784.7
NET AMOUNT	0	0
Other assets excluding derivatives and non financial instruments	10,200	10,300
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	923.3	3,006.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	699	2,937.2
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	224.3	69.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	3.6	12.2
NET AMOUNT	220.7	56.9
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	399.5	301.4
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	215.2	189.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	184.3	111.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	184.3	111.9
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	4.5	0.1
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	4.5	0.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	$ 4.5	$ 0.1

Offsetting of Assets and Liab_4

Offsetting of Assets and Liabilities (Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	$ 1,630.2	$ 2,806.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,070.1	2,205.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	560.1	600.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	560.1	600.9
Total Derivatives Not Subject to a Master Netting Arrangement
Total Derivatives Not Subject to a Master Netting Arrangement	186.8	843.5
Offsetting Derivative Liabilities [Abstract]
GROSS RECOGNIZED LIABILITIES	1,817	3,649.8
Derivative Liabilities	746.9	1,444.4
NET AMOUNT	746.9	1,444.4
Securities Sold under Agreements to Repurchase
GROSS RECOGNIZED LIABILITIES	66,375.9	62,860.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	65,864.5	62,075.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	511.4	784.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	511.4	784.7
NET AMOUNT	0	0
Other liabilities	2,900	4,000
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	1,131.3	2,411.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,051.2	2,175.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	80.1	236
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	80.1	236
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	477.7	368.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2.7	6
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	475	362.3
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	475	362.3
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	0.2	0.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	0.2	0.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	0.2	0.9
Other Financial Derivatives | Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	21	25.4
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	16.2	23.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	4.8	1.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	$ 4.8	$ 1.7

Offsetting of Assets and Liab_5

Offsetting of Assets and Liabilities (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Offsetting Assets and Liabilities [Line Items]
Collateral received	$ 3.6	$ 12.2
Gross amounts not offset in the balance sheet	0	0
Aggregate fair value of all derivative instruments with credit-risk-related contingent features that are in a liability position	92.7	1,200
Collateral deposited with derivative counterparties for derivatives instruments with credit-risk-related contingent features that are in a liability position	75.3	1,100
Net maximum amount of termination payments that could have been required	17.4	52.2
Net Investment Hedges
Offsetting Assets and Liabilities [Line Items]
Collateral received	78.3
Gross amounts not offset in the balance sheet	$ 60.5
Cash collateral received from derivative counterparties and not offset against derivative assets		373.1
Cash collateral deposited with derivative counterparties not offset against derivative liabilities		$ 21.3