Northern Trust (NTRS) 10-Q 31 Oct 23 2023 Q3 Quarterly report Financial data

Cover Page

Cover Page	9 Months Ended
	Sep. 30, 2023 shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
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)	207,036,370
Amendment Flag	false
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	Q3
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	Sep. 30, 2023	Dec. 31, 2022
ASSETS
Cash and Due from Banks	$ 4,955.7	$ 4,654.2
Federal Reserve and Other Central Bank Deposits	32,316.8	40,030.4
Interest-Bearing Deposits with Banks	2,122.5	1,941.1
Federal Funds Sold	0	32
Securities Purchased under Agreements to Resell	384.3	1,070.3
Debt Securities
Available for Sale	24,342.1	26,699.9
Held to Maturity	24,920.4	25,036.1
Trading Account	0.1	95.2
Total Debt Securities	49,262.6	51,831.2
Loans
Total Loans (Net of unearned income of $5.9 and $9.0)	43,577	42,893.3
Allowance for Credit Losses	(182.7)	(161.1)
Buildings and Equipment	465	500.5
Client Security Settlement Receivables	147.6	1,698.3
Goodwill	692.8	691.3
Other Assets	12,589	9,855.2
Total Assets	146,330.6	155,036.7
Deposits
Demand and Other Noninterest-Bearing	12,925.1	16,582.7
Savings, Money Market and Other Interest-Bearing	24,362.6	31,128.6
Savings Certificates and Other Time	4,038.6	1,981.3
Non U.S. Offices — Noninterest-Bearing	8,012.7	8,757.6
Non U.S. Offices — Interest-Bearing	60,826.9	65,481.9
Total Deposits	110,165.9	123,932.1
Federal Funds Purchased	5,539.3	1,896.9
Securities Sold Under Agreements to Repurchase	545.9	567.2
Other Borrowings	6,870.9	7,592.3
Senior Notes	2,688.9	2,724.2
Long-Term Debt	4,060.7	2,066.2
Other Liabilities	4,611.8	4,998.3
Total Liabilities	134,483.4	143,777.2
STOCKHOLDERS' EQUITY
Common Stock	408.6	408.6
Additional Paid-In Capital	993.1	983.5
Retained Earnings	14,281.6	13,798.5
Accumulated Other Comprehensive Loss	(1,363.4)	(1,569.2)
Treasury Stock	(3,357.6)	(3,246.8)
Total Stockholders’ Equity	11,847.2	11,259.5
Total Liabilities and Stockholders’ Equity	146,330.6	155,036.7
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 $5.9 and $9.0)	21,987.3	21,635.6
Personal
Loans
Total Loans (Net of unearned income of $5.9 and $9.0)	$ 21,589.7	$ 21,257.7

Consolidated Balance Sheets (_2

Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Available-for-sale securities, amortized cost	$ 25,246.1	$ 27,760
Held to maturity, fair value	22,449.7	22,879.3
Unearned income	$ 5.9	$ 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)	207,036,370	208,428,309
Treasury stock, (in shares)	38,135,154	36,743,215
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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,111.9	$ 1,078.7	$ 3,271.8	$ 3,390.5
Foreign Exchange Trading Income	51.8	64.7	154.9	223.2
Treasury Management Fees	7.5	9.3	23.8	31
Security Commissions and Trading Income	30.9	32.1	101.7	101.1
Other Operating Income	68.2	57.3	170.2	144
Investment Security Gains (Losses), net	0	(0.3)	6.9	(0.3)
Total Noninterest Income	1,270.3	1,241.8	3,729.3	3,889.5
Net Interest Income
Interest Income	1,935	799.3	5,125.4	1,707.6
Interest Expense	1,478.8	286.3	3,626.5	354.9
Net Interest Income	456.2	513	1,498.9	1,352.7
Provision for Credit Losses	14	0.5	13.5	7
Net Interest Income after Provision for Credit Losses	442.2	512.5	1,485.4	1,345.7
Noninterest Expense
Compensation	558.1	553.3	1,757.8	1,663.7
Employee Benefits	100.8	109.9	303.2	333.8
Outside Services	229.6	220.9	671.3	647.4
Equipment and Software	232.5	212.4	693.5	609.4
Occupancy	58.7	51.3	173.8	153.4
Other Operating Expense	98.5	82	296.1	251.6
Total Noninterest Expense	1,278.2	1,229.8	3,895.7	3,659.3
Income before Income Taxes	434.3	524.5	1,319	1,575.9
Provision for Income Taxes	106.5	129.7	324.8	395.6
Net Income	327.8	394.8	994.2	1,180.3
Preferred Stock Dividends	16.2	16.2	37.1	37.1
Net Income Applicable to Common Stock	$ 311.6	$ 378.6	$ 957.1	$ 1,143.2
Per Common Share
Net Income — Basic (in dollars per share)	$ 1.49	$ 1.80	$ 4.56	$ 5.44
Net Income - Diluted (in dollars per share)	$ 1.49	$ 1.80	$ 4.56	$ 5.43
Average Number of Common Shares Outstanding
Basic (in shares)	207,021,554	208,400,135	207,611,420	208,271,070
Diluted (in shares)	207,252,992	208,888,572	207,927,720	208,858,976

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Statement of Comprehensive Income [Abstract]
Net Income	$ 327.8	$ 394.8	$ 994.2	$ 1,180.3
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Available for Sale Debt Securities	32.3	(272.2)	170.5	(1,674)
Net Unrealized Gains (Losses) on Cash Flow Hedges	(0.4)	2.1	(1.1)	5.1
Net Foreign Currency Adjustments	9.6	20.2	34.2	2.6
Net Pension and Other Postretirement Benefit Adjustments	1	(24.5)	2.2	(83.1)
Net Change	42.5	(274.4)	205.8	(1,749.4)
Comprehensive Income (Loss)	$ 370.3	$ 120.4	$ 1,200	$ (569.1)

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, 2021	$ 12,016.8	$ 884.9	$ 408.6	$ 939.3	$ 13,117.3	$ (35.6)	$ (3,297.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	389.3				389.3
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	(871.4)					(871.4)
Dividends Declared:
Common Stock	(147.8)				(147.8)
Preferred Stock	(16.2)				(16.2)
Stock Awards and Options Exercised	72.9			(7.6)			80.5
Stock Purchased	(33.8)						(33.8)
Ending balance at Mar. 31, 2022	11,409.8	884.9	408.6	931.7	13,342.6	(907)	(3,251)
Beginning balance at Dec. 31, 2021	12,016.8	884.9	408.6	939.3	13,117.3	(35.6)	(3,297.7)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	1,180.3
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	(1,749.4)
Dividends Declared:
Stock Purchased	(35.2)
Ending balance at Sep. 30, 2022	11,030.4	884.9	408.6	963.6	13,806.3	(1,785)	(3,248)
Beginning balance at Mar. 31, 2022	11,409.8	884.9	408.6	931.7	13,342.6	(907)	(3,251)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	396.2				396.2
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	(603.6)					(603.6)
Dividends Declared:
Common Stock	(148)				(148)
Preferred Stock	(4.7)				(4.7)
Stock Awards and Options Exercised	20.3			19.4			0.9
Stock Purchased	(0.3)						(0.3)
Ending balance at Jun. 30, 2022	11,069.7	884.9	408.6	951.1	13,586.1	(1,510.6)	(3,250.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	394.8				394.8
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	(274.4)					(274.4)
Dividends Declared:
Common Stock	(158.4)				(158.4)
Preferred Stock	(16.2)				(16.2)
Stock Awards and Options Exercised	16.1			12.5			3.6
Stock Purchased	(1.2)						(1.2)
Ending balance at Sep. 30, 2022	11,030.4	884.9	408.6	963.6	13,806.3	(1,785)	(3,248)
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, 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	994.2
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	205.8
Dividends Declared:
Stock Purchased	(201.3)
Ending balance at Sep. 30, 2023	11,847.2	884.9	408.6	993.1	14,281.6	(1,363.4)	(3,357.6)
Beginning balance at Mar. 31, 2023	11,587.8	884.9	408.6	964.5	13,958.3	(1,366.2)	(3,262.3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	331.8				331.8
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	(39.7)					(39.7)
Dividends Declared:
Common Stock	(157.8)				(157.8)
Preferred Stock	(4.7)				(4.7)
Stock Awards and Options Exercised	17.6			15.5			2.1
Stock Purchased	(99.3)						(99.3)
Ending balance at Jun. 30, 2023	11,635.7	884.9	408.6	980	14,127.6	(1,405.9)	(3,359.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	327.8				327.8
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	42.5					42.5
Dividends Declared:
Common Stock	(157.6)				(157.6)
Preferred Stock	(16.2)				(16.2)
Stock Awards and Options Exercised	17.2			13.1			4.1
Stock Purchased	(1.1)						(1.1)
Excise Tax on Share Repurchases	(1.1)						(1.1)
Ending balance at Sep. 30, 2023	$ 11,847.2	$ 884.9	$ 408.6	$ 993.1	$ 14,281.6	$ (1,363.4)	$ (3,357.6)

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022
Statement of Stockholders' Equity [Abstract]
Common stock dividends (in usd per share)	$ 0.75	$ 0.75	$ 0.75	$ 0.75	$ 0.70	$ 0.70

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income	$ 994.2	$ 1,180.3
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Investment Security Gains	(6.9)	0.3
Amortization and Accretion of Securities and Unearned Income, net	5.8	51.5
Provision for Credit Losses	13.5	7
Depreciation and Amortization	465.6	405.4
Pension Plan Contributions	(16.5)	(20.7)
Change in Receivables	(200.3)	(107.8)
Change in Interest Payable	88.8	92.6
Change in Collateral With Derivative Counterparties, net	(1,857.5)	(3,089.5)
Other Operating Activities, net	335.7	(278.7)
Net Cash Used in Operating Activities	(177.6)	(1,759.6)
CASH FLOWS FROM INVESTING ACTIVITIES
Change in Federal Funds Sold	(32)	(30.1)
Change in Securities Purchased under Agreements to Resell	717.5	(550.6)
Change in Interest-Bearing Deposits with Banks	(203)	193.7
Net Change in Federal Reserve and Other Central Bank Deposits	7,760.3	22,777
Purchases of Held to Maturity Debt Securities	(25,821.1)	(27,309.4)
Proceeds from the Maturity and Redemption of Held to Maturity Debt Securities	25,872.9	31,071.5
Purchases of Available for Sale Debt Securities	(4,412)	(3,777.9)
Proceeds from the Maturity and Sales of Available for Sale Debt Securities	6,912.5	5,524.9
Change in Loans	(681.6)	(3,607.7)
Purchases of Buildings and Equipment	(52.7)	(70.7)
Purchases and Development of Computer Software	(412.8)	(425.2)
Change in Client Security Settlement Receivables	1,555	(1,170.3)
Bank-Owned Life Insurance Policy Premiums	0	(500)
Other Investing Activities, net	(1,555.9)	(351.7)
Net Cash Provided by Investing Activities	9,647.1	21,773.5
CASH FLOWS FROM FINANCING ACTIVITIES
Change in Deposits	(13,089.4)	(26,117.2)
Change in Federal Funds Purchased	3,642.4	4,364.6
Change in Securities Sold under Agreements to Repurchase	(21.3)	29.4
Change in Short-Term Other Borrowings	(717.4)	3,565.8
Proceeds from Long Term Debt	2,000	0
Proceeds from Senior Notes	0	995.4
Repayments of Senior Notes	0	(500)
Treasury Stock Purchased	(201.3)	(35.3)
Net Proceeds from Stock Options	1.9	3.4
Cash Dividends Paid on Common Stock	(467.3)	(437.5)
Cash Dividends Paid on Preferred Stock	(37.1)	(25.6)
Other Financing Activities, net	(1.2)	0.2
Net Cash Used in Financing Activities	(8,890.7)	(18,156.8)
Effect of Foreign Currency Exchange Rates on Cash	(277.3)	(421.1)
Change in Cash and Due from Banks	301.5	1,436
Cash and Due from Banks at Beginning of Period	4,654.2	3,056.8
Cash and Due from Banks at End of Period	4,955.7	4,492.8
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest Paid	3,536.9	263.4
Income Taxes Paid	211.1	295.3
Transfers from Loans to OREO	0.2	0
Transfers from Available for Sale Debt Securities to Held to Maturity Debt Securities	$ 0	$ 6,623.3

Basis of Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of PresentationThe 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 September 30, 2023 and 2022, 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, 2022.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2023
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements On January 1, 2023, Northern Trust adopted Accounting Standards Update (ASU) No. 2022-01, “Derivatives and Hedging (Topic 815): Fair Value Hedging—Portfolio Layer Method” (ASU 2022-01). The amendments in ASU 2022-01 expand the current last-of-layer hedging model from a single-layer method to allow multiple hedged layers of a single closed portfolio. To reflect that expansion, the last-of-layer method is renamed the portfolio layer method. In addition, ASU 2022-01 (1) expands the scope of the portfolio layer method to include non-prepayable assets, (2) specifies eligible hedging instruments in a single-layer hedge, (3) provides additional guidance on the accounting for and disclosure of hedge basis adjustments under the portfolio layer method, and (4) specifies how hedge basis adjustments should be considered when determining credit losses for the assets included in the closed portfolio. Upon adoption of ASU 2022-01, there was no impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. On January 1, 2023, Northern Trust adopted ASU No. 2022-02, “Financial Instruments—Credit Losses (Topic 326): Troubled Debt Restructurings and Vintage Disclosures” (ASU 2022-02). The amendments in ASU 2022-02 eliminate the accounting guidance for troubled debt restructurings (TDRs) for creditors that have adopted the current expected credit losses accounting standard while enhancing disclosure requirements for certain loan refinancings and restructurings made to borrowers experiencing financial difficulty. In addition, ASU 2022-02 requires that a public business entity disclose current-period gross charge-offs by year of origination for financing receivables and net investment in leases. Upon adoption of ASU 2022-02, there was no significant impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. Please refer to Note 5—Loans for further information. On January 1, 2023, Northern Trust adopted ASU No. 2022-04, “Liabilities—Supplier Finance Programs (Topic 405-50): Disclosure of Supplier Finance Program Obligations” (ASU 2022-04). The amendments in ASU 2022-04 enhance the transparency about the use of supplier finance programs for investors or other allocators of capital. Specifically, ASU 2022-04 requires that a buyer in a supplier finance program disclose sufficient qualitative and quantitative information about the program to allow a user of financial statements to understand the program’s nature, activity during the period, changes from period to period, and potential magnitude. Upon adoption of ASU 2022-04, there was no impact to Northern Trust’s consolidated balance sheets or consolidated statements of income.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2023
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 nine months ended September 30, 2023 or the year ended December 31, 2022. 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 September 30, 2023, Northern Trust’s AFS debt securities portfolio included 1,009 Level 2 debt securities with an aggregate market value of $21.5 billion. Substantially all were valued by external pricing vendors. As of December 31, 2022, Northern Trust’s AFS debt securities portfolio included 1,163 Level 2 debt securities with an aggregate market value of $24.0 billion. All 1,163 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 September 30, 2023 and December 31, 2022, 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 35: LEVEL 3 SIGNIFICANT UNOBSERVABLE INPUTS SEPTEMBER 30, 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 $28.9 million Discounted Cash Flow Conversion Rate 1.59x 1.59x Visa Class A Appreciation 10.15% 10.15% Expected Duration 12 - 30 months 16 months (1) Weighted average of expected duration based on scenario probability. DECEMBER 31, 2022 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 $34.8 million Discounted Cash Flow Conversion Rate 1.60x 1.60x Visa Class A Appreciation 8.53% 8.53% Expected Duration 12 - 33 months 20 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 September 30, 2023 and December 31, 2022, segregated by fair value hierarchy level. TABLE 36: RECURRING BASIS HIERARCHY LEVELING SEPTEMBER 30, 2023 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 2,879.4 $ — $ — $ — $ 2,879.4 Obligations of States and Political Subdivisions — 282.1 — — 282.1 Government Sponsored Agency — 11,656.8 — — 11,656.8 Non-U.S. Government — 246.9 — — 246.9 Corporate Debt — 380.9 — — 380.9 Covered Bonds — 280.4 — — 280.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,959.8 — — 2,959.8 Other Asset-Backed — 4,771.5 — — 4,771.5 Commercial Mortgage-Backed — 884.3 — — 884.3 Total Available for Sale 2,879.4 21,462.7 — — 24,342.1 Trading Account — 0.1 — — 0.1 Total Available for Sale and Trading Debt Securities 2,879.4 21,462.8 — — 24,342.2 Other Assets Money Market Investment 95.0 — — — 95.0 Derivative Assets Foreign Exchange Contracts — 3,049.1 — (1,266.6) 1,782.5 Interest Rate Contracts — 363.9 — (286.5) 77.4 Other Financial Derivatives — — — — — Total Derivative Assets — 3,413.0 — (1,553.1) 1,859.9 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 2,820.2 — (2,380.6) 439.6 Interest Rate Contracts — 467.3 — (2.1) 465.2 Other Financial Derivatives (1) — — 28.9 (27.2) 1.7 Total Derivative Liabilities $ — $ 3,287.5 $ 28.9 $ (2,409.9) $ 906.5 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 September 30, 2023, derivative assets and liabilities shown above also include reductions of $287.0 million and $1.1 billion, respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1) This line consists of swaps related to the sale of certain Visa Class B common shares. DECEMBER 31, 2022 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 2,747.4 $ — $ — $ — $ 2,747.4 Obligations of States and Political Subdivisions — 787.6 — — 787.6 Government Sponsored Agency — 11,545.2 — — 11,545.2 Non-U.S. Government — 360.0 — — 360.0 Corporate Debt — 1,747.6 — — 1,747.6 Covered Bonds — 388.7 — — 388.7 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,479.4 — — 2,479.4 Other Asset-Backed — 5,256.2 — — 5,256.2 Commercial Mortgage-Backed — 1,387.8 — — 1,387.8 Total Available for Sale 2,747.4 23,952.5 — — 26,699.9 Trading Account 95.0 0.2 — — 95.2 Total Available for Sale and Trading Debt Securities 2,842.4 23,952.7 — — 26,795.1 Other Assets Derivative Assets Foreign Exchange Contracts — 3,510.1 — (2,666.4) 843.7 Interest Rate Contracts — 222.0 — (144.3) 77.7 Other Financial Derivatives (1) — 0.3 — — 0.3 Total Derivative Assets — 3,732.4 — (2,810.7) 921.7 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 3,187.5 — (1,826.7) 1,360.8 Interest Rate Contracts — 431.8 — (5.9) 425.9 Other Financial Derivatives (2) — — 34.8 (33.3) 1.5 Total Derivative Liabilities $ — $ 3,619.3 $ 34.8 $ (1,865.9) $ 1,788.2 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, 2022, derivative assets and liabilities shown above also include reductions of $1.1 billion and $195.3 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1) This line consists of total return swap contracts. (2) This line 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 and nine months ended September 30, 2023 and 2022. TABLE 37: CHANGES IN LEVEL 3 LIABILITIES (In Millions) SWAPS RELATED TO SALE OF CERTAIN VISA CLASS B COMMON SHARES THREE MONTHS ENDED SEPTEMBER 30, 2023 2022 Fair Value at July 1 $ 36.4 $ 31.1 Total (Gains) Losses: Included in Earnings (1) (2.4) 1.1 Purchases, Issues, Sales, and Settlements Settlements (5.1) (4.6) Fair Value at September 30 $ 28.9 $ 27.6 (1) (Gains) losses are recorded in Other Operating Income on the consolidated statements of income. NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 Fair Value at January 1 $ 34.8 $ 37.5 Total (Gains) Losses: Included in Earnings (1) 16.1 11.2 Purchases, Issues, Sales, and Settlements Settlements (22.0) (21.1) Fair Value at September 30 $ 28.9 $ 27.6 (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 September 30, 2023 and December 31, 2022, 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 were subject to adjustments to reflect management’s judgment as to realizable value and consisted of a discount factor of 20.0% with a weighted average based on fair values of 20.0%, and a range of discount factors from 15.0% to 20.0% with a weighted average of 17.2%, as of September 30, 2023 and December 31, 2022, respectively. 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. Collateral-dependent nonaccrual loans that have been adjusted to fair value totaled $3.8 million and $6.6 million at September 30, 2023 and December 31, 2022, respectively. 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 September 30, 2023 and December 31, 2022, 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 38: LEVEL 3 NONRECURRING BASIS SIGNIFICANT UNOBSERVABLE INPUTS SEPTEMBER 30, 2023 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $3.8 million Market Approach Discount factor applied to real estate collateral-dependent loans to reflect realizable value 20.0% 20.0% (1) Includes real estate collateral-dependent loans and other collateral-dependent loans. DECEMBER 31, 2022 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $6.6 million Market Approach Discount factor applied to real estate collateral-dependent loans to reflect realizable value 15.0 % - 20.0% 17.2% (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 September 30, 2023 and December 31, 2022. The following tables exclude those items measured at fair value on a recurring basis. TABLE 39: FAIR VALUE OF FINANCIAL INSTRUMENTS SEPTEMBER 30, 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 $ 4,955.7 $ 4,955.7 $ 4,955.7 $ — $ — Federal Reserve and Other Central Bank Deposits 32,316.8 32,316.8 — 32,316.8 — Interest-Bearing Deposits with Banks 2,122.5 2,122.5 — 2,122.5 — Securities Purchased under Agreements to Resell 384.3 384.3 — 384.3 — Debt Securities - Held to Maturity 24,920.4 22,449.7 — 22,449.7 — Loans Held for Investment 43,410.2 43,384.4 — — 43,384.4 Other Assets 1,502.1 1,485.4 89.4 1,396.0 — FINANCIAL LIABILITIES Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 45,300.4 $ 45,300.4 $ 45,300.4 $ — $ — Savings Certificates and Other Time 4,038.6 4,070.4 — 4,070.4 — Non U.S. Offices Interest-Bearing 60,826.9 60,826.9 — 60,826.9 — Federal Funds Purchased 5,539.3 5,539.3 — 5,539.3 — Securities Sold Under Agreements to Repurchase 545.9 545.9 — 545.9 — Other Borrowings 6,870.9 6,888.1 — 6,888.1 — Senior Notes 2,688.9 2,646.6 — 2,646.6 — Long-Term Debt 4,060.7 4,026.1 — 4,026.1 — Unfunded Commitments 205.5 205.5 — 205.5 — Other Liabilities 89.5 89.5 — — 89.5 DECEMBER 31, 2022 ESTIMATED FAIR VALUE (In Millions) BOOK VALUE TOTAL ESTIMATED FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 FINANCIAL ASSETS Cash and Due from Banks $ 4,654.2 $ 4,654.2 $ 4,654.2 $ — $ — Federal Reserve and Other Central Bank Deposits 40,030.4 40,030.4 — 40,030.4 — Interest-Bearing Deposits with Banks 1,941.1 1,941.1 — 1,941.1 — Federal Funds Sold 32.0 32.0 — 32.0 — Securities Purchased under Agreements to Resell 1,070.3 1,070.3 — 1,070.3 — Debt Securities - Held to Maturity 25,036.1 22,879.3 50.0 22,829.3 — Loans Held for Investment 42,749.0 42,636.5 — — 42,636.5 Other Assets 1,476.9 1,460.4 94.7 1,365.7 — FINANCIAL LIABILITIES Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 56,468.9 $ 56,468.9 $ 56,468.9 $ — $ — Savings Certificates and Other Time 1,981.3 1,976.1 — 1,976.1 — Non U.S. Offices Interest-Bearing 65,481.9 65,481.9 — 65,481.9 — Federal Funds Purchased 1,896.9 1,896.9 — 1,896.9 — Securities Sold Under Agreements to Repurchase 567.2 567.2 — 567.2 — Other Borrowings 7,592.3 7,592.8 — 7,592.8 — Senior Notes 2,724.2 2,729.8 — 2,729.8 — Long-Term Debt 2,066.2 2,110.7 — 2,110.7 — Unfunded Commitments 218.9 218.9 — 218.9 — Other Liabilities 73.2 73.2 — — 73.2

Securities

Securities	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022, and remaining maturities of AFS debt securities as of September 30, 2023. TABLE 40: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF AVAILABLE FOR SALE DEBT SECURITIES SEPTEMBER 30, 2023 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 2,981.2 $ — $ 101.8 $ 2,879.4 Obligations of States and Political Subdivisions 301.5 — 19.4 282.1 Government Sponsored Agency 11,988.1 6.8 338.1 11,656.8 Non-U.S. Government 271.0 — 24.1 246.9 Corporate Debt 397.9 0.1 17.1 380.9 Covered Bonds 292.2 0.1 11.9 280.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,099.2 1.0 140.4 2,959.8 Other Asset-Backed 4,966.1 1.0 195.6 4,771.5 Commercial Mortgage-Backed 948.9 0.1 64.7 884.3 Total $ 25,246.1 $ 9.1 $ 913.1 $ 24,342.1 DECEMBER 31, 2022 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 2,837.7 $ 2.5 $ 92.8 $ 2,747.4 Obligations of States and Political Subdivisions 817.8 — 30.2 787.6 Government Sponsored Agency 11,892.5 4.3 351.6 11,545.2 Non-U.S. Government 387.6 — 27.6 360.0 Corporate Debt 1,774.3 0.2 26.9 1,747.6 Covered Bonds 403.1 0.3 14.7 388.7 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,645.8 0.3 166.7 2,479.4 Other Asset-Backed 5,544.3 — 288.1 5,256.2 Commercial Mortgage-Backed 1,456.9 0.1 69.2 1,387.8 Total $ 27,760.0 $ 7.7 $ 1,067.8 $ 26,699.9 TABLE 41: REMAINING MATURITY OF AVAILABLE FOR SALE DEBT SECURITIES SEPTEMBER 30, 2023 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 $ 297.3 $ 296.4 $ 2,683.9 $ 2,583.0 $ — $ — $ — $ — $ 2,981.2 $ 2,879.4 Obligations of States and Political Subdivisions — — 109.1 102.8 192.4 179.3 — — 301.5 282.1 Government Sponsored Agency 2,294.8 2,250.7 5,259.3 5,113.8 3,481.1 3,389.9 952.9 902.4 11,988.1 11,656.8 Non-U.S. Government — — 271.0 246.9 — — — — 271.0 246.9 Corporate Debt 150.4 148.2 230.9 218.8 16.6 13.9 — — 397.9 380.9 Covered Bonds 141.6 140.1 150.6 140.3 — — — — 292.2 280.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 569.8 563.0 2,465.3 2,347.1 64.1 49.7 — — 3,099.2 2,959.8 Other Asset-Backed 731.5 711.3 3,985.4 3,815.4 248.9 244.5 0.3 0.3 4,966.1 4,771.5 Commercial Mortgage-Backed 38.8 36.7 765.8 729.2 144.3 118.4 — — 948.9 884.3 Total $ 4,224.2 $ 4,146.4 $ 15,921.3 $ 15,297.3 $ 4,147.4 $ 3,995.7 $ 953.2 $ 902.7 $ 25,246.1 $ 24,342.1 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 September 30, 2023 and December 31, 2022. TABLE 42: AVAILABLE FOR SALE DEBT SECURITIES IN UNREALIZED LOSS POSITION WITH NO CREDIT LOSSES REPORTED SEPTEMBER 30, 2023 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ 1,551.0 $ 12.1 $ 1,183.0 $ 89.7 $ 2,734.0 $ 101.8 Obligations of States and Political Subdivisions — — 282.1 19.4 282.1 19.4 Government Sponsored Agency 2,855.0 18.1 7,865.9 320.0 10,720.9 338.1 Non-U.S. Government — — 246.9 24.1 246.9 24.1 Corporate Debt 12.4 0.3 229.9 9.9 242.3 10.2 Covered Bonds — — 214.8 11.9 214.8 11.9 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 302.6 1.9 1,898.2 138.5 2,200.8 140.4 Other Asset-Backed — — 4,561.6 195.6 4,561.6 195.6 Commercial Mortgage-Backed — — 856.7 64.7 856.7 64.7 Total $ 4,721.0 $ 32.4 $ 17,339.1 $ 873.8 $ 22,060.1 $ 906.2 Note: Three corporate debt AFS securities with a fair value of $81.5 million and unrealized losses of $6.9 million have been excluded from the table above as these AFS securities have a $0.7 million allowance for credit losses reported as of September 30, 2023. Refer to the discussion further below and Note 6—Allowance for Credit Losses for further information. DECEMBER 31, 2022 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ 1,123.6 $ 64.1 $ 343.1 $ 28.7 $ 1,466.7 $ 92.8 Obligations of States and Political Subdivisions 160.0 16.8 120.6 13.4 280.6 30.2 Government Sponsored Agency 7,631.4 262.1 2,737.7 89.5 10,369.1 351.6 Non-U.S. Government 235.4 17.3 124.6 10.3 360.0 27.6 Corporate Debt 427.3 14.6 130.3 2.8 557.6 17.4 Covered Bonds 238.0 13.5 42.8 1.2 280.8 14.7 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 1,305.4 74.4 807.1 83.2 2,112.5 157.6 Other Asset-Backed 3,873.4 217.5 1,247.6 70.6 5,121.0 288.1 Commercial Mortgage-Backed 670.9 47.4 215.6 21.8 886.5 69.2 Total $ 15,665.4 $ 727.7 $ 5,769.4 $ 321.5 $ 21,434.8 $ 1,049.2 Note: Three corporate debt AFS securities with a fair value of $93.8 million and unrealized losses of $9.5 million and one sub-sovereign, supranational and non-U.S. agency bonds AFS security with a fair value of $68.3 million and unrealized loss of $9.1 million have been excluded from the table above as these AFS securities have a $1.3 million allowance for credit losses reported as of December 31, 2022. Refer to the discussion further below and Note 6—Allowance for Credit Losses for further information. As of September 30, 2023, 1,044 AFS debt securities with a combined fair value of $22.1 billion were in an unrealized loss position without an allowance for credit losses, with their unrealized losses totaling $906.2 million. As of September 30, 2023, unrealized losses related to AFS debt securities of $338.1 million, $195.6 million, and $140.4 million related to government-sponsored agency securities, other asset-backed and sub-sovereign, supranational and non-U.S. agency bonds, respectively, which are primarily attributable to higher intermediate rates. As of December 31, 2022, 1,030 AFS debt securities with a combined fair value of $21.4 billion were in an unrealized loss position without an allowance for credit losses, with their unrealized losses totaling $1.0 billion. As of December 31, 2022, unrealized losses related to AFS debt securities of $351.6 million, $288.1 million, and $157.6 million related to government-sponsored agency, other asset-backed, and sub-sovereign, supranational and non-U.S. agency bonds, respectively, which are primarily attributable to changes in overall market interest rates and credit spreads since their purchase. As of December 31, 2022, the Corporation intended to sell certain AFS debt securities that were in an unrealized loss position. The securities were written down to their fair value of $2.1 billion with a $213.0 million loss recognized in Investment Security Gains (Losses), net on the consolidated statements of income for the period ended December 31, 2022. In January 2023, the securities were subsequently sold resulting in an incremental $6.9 million gain upon sale as compared to the fair value recorded on the consolidated balance sheets at December 31, 2022. 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 and 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. There was a $0.6 million release of credit reserves for AFS securities for both the three and nine months ended September 30, 2023. There was a $0.9 million release of credit reserves and an $0.8 million provision for credit losses for AFS securities for the three and nine months ended September 30, 2022, respectively. There was a $0.7 million allowance for credit losses for AFS securities as of September 30, 2023 which was primarily corporate debt securities and $1.3 million allowance for credit losses for AFS securities as of December 31, 2022. 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 September 30, 2023 and December 31, 2022, and remaining maturities of HTM debt securities as of September 30, 2023. TABLE 43: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF HELD TO MATURITY DEBT SECURITIES SEPTEMBER 30, 2023 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR Obligations of States and Political Subdivisions $ 2,577.7 $ — $ 177.9 $ 2,399.8 Government Sponsored Agency 9,159.9 — 1,405.6 7,754.3 Non-U.S. Government 3,711.8 0.1 126.6 3,585.3 Corporate Debt 639.1 — 38.0 601.1 Covered Bonds 2,116.9 0.4 142.0 1,975.3 Certificates of Deposit 405.4 0.1 — 405.5 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 5,443.8 1.3 400.3 5,044.8 Other Asset-Backed 246.6 1.0 0.2 247.4 Commercial Mortgage-Backed 37.6 — 0.7 36.9 Other 581.6 — 182.3 399.3 Total $ 24,920.4 $ 2.9 $ 2,473.6 $ 22,449.7 DECEMBER 31, 2022 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR U.S. Government $ 50.0 $ — $ — $ 50.0 Obligations of States and Political Subdivisions 2,565.3 — 149.8 2,415.5 Government Sponsored Agency 9,407.7 — 1,076.0 8,331.7 Non-U.S. Government 3,234.0 0.1 133.8 3,100.3 Corporate Debt 713.3 — 45.4 667.9 Covered Bonds 2,530.3 0.3 158.7 2,371.9 Certificates of Deposit 35.9 — — 35.9 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 5,703.3 1.0 436.1 5,268.2 Other Asset-Backed 263.7 — 1.0 262.7 Other 532.6 — 157.4 375.2 Total $ 25,036.1 $ 1.4 $ 2,158.2 $ 22,879.3 As of September 30, 2023, the $24.9 billion HTM debt securities portfolio had unrealized losses of $1.4 billion and $400.3 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, 2022, the $25.0 billion HTM debt securities portfolio had unrealized losses of $1.1 billion and $436.1 million related to government-sponsored agency and sub-sovereign, supranational and non-U.S. agency bonds, respectively, which are primarily attributable to changes in overall market interest rates and credit spreads since their purchase. TABLE 44: REMAINING MATURITY OF HELD TO MATURITY DEBT SECURITIES SEPTEMBER 30, 2023 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 $ 58.1 $ 56.9 $ 988.1 $ 941.6 $ 1,187.1 $ 1,095.1 $ 344.4 $ 306.2 $ 2,577.7 $ 2,399.8 Government Sponsored Agency 859.7 727.6 3,105.8 2,649.4 3,408.4 2,901.4 1,786.0 1,475.9 9,159.9 7,754.3 Non-U.S. Government 2,341.3 2,337.5 1,338.1 1,221.1 32.4 26.7 — — 3,711.8 3,585.3 Corporate Debt 96.2 94.6 528.0 494.6 14.9 11.9 — — 639.1 601.1 Covered Bonds 135.5 132.6 1,678.3 1,582.7 303.1 260.0 — — 2,116.9 1,975.3 Certificates of Deposit 405.4 405.5 — — — — — — 405.4 405.5 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 817.0 810.2 4,604.4 4,216.8 22.4 17.8 — — 5,443.8 5,044.8 Other Asset-Backed 43.8 43.7 93.0 93.2 109.8 110.5 — — 246.6 247.4 Commercial Mortgage-Backed — — 37.6 36.9 — — — — 37.6 36.9 Other 34.9 33.6 338.9 292.8 29.8 21.0 178.0 51.9 581.6 399.3 Total $ 4,791.9 $ 4,642.2 $ 12,712.2 $ 11,529.1 $ 5,107.9 $ 4,444.4 $ 2,308.4 $ 1,834.0 $ 24,920.4 $ 22,449.7 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 45: AMORTIZED COST OF HELD TO MATURITY DEBT SECURITIES BY CREDIT RATING SEPTEMBER 30, 2023 (In Millions) AAA AA A BBB NOT RATED TOTAL Obligations of States and Political Subdivisions $ 918.0 $ 1,659.7 $ — $ — $ — $ 2,577.7 Government Sponsored Agency 9,159.9 — — — — 9,159.9 Non-U.S. Government 894.1 879.0 1,619.7 319.0 — 3,711.8 Corporate Debt 2.2 299.2 337.7 — — 639.1 Covered Bonds 2,116.9 — — — — 2,116.9 Certificates of Deposit 367.4 — — — 38.0 405.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 4,162.6 1,251.3 28.8 1.1 — 5,443.8 Other Asset-Backed 246.6 — — — — 246.6 Commercial Mortgage-Backed 37.6 — — — — 37.6 Other 56.0 — — — 525.6 581.6 Total $ 17,961.3 $ 4,089.2 $ 1,986.2 $ 320.1 $ 563.6 $ 24,920.4 Percent of Total 72 % 17 % 8 % 1 % 2 % 100 % DECEMBER 31, 2022 (In Millions) AAA AA A BBB NOT RATED TOTAL U.S. Government $ 50.0 $ — $ — $ — $ — $ 50.0 Obligations of States and Political Subdivisions 926.8 1,638.5 — — — 2,565.3 Government Sponsored Agency 9,407.7 — — — — 9,407.7 Non-U.S. Government 762.2 926.5 1,223.0 322.3 — 3,234.0 Corporate Debt 2.1 305.7 405.5 — — 713.3 Covered Bonds 2,530.3 — — — — 2,530.3 Certificates of Deposit — — — — 35.9 35.9 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 4,171.3 1,502.0 28.9 1.1 — 5,703.3 Other Asset-Backed 263.7 — — — — 263.7 Other 65.8 — — — 466.8 532.6 Total $ 18,179.9 $ 4,372.7 $ 1,657.4 $ 323.4 $ 502.7 $ 25,036.1 Percent of Total 73 % 17 % 7 % 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 97% of the HTM portfolio at both September 30, 2023 and December 31, 2022 comprised of securities rated A or higher. The remaining HTM debt securities portfolio was comprised of 1% rated BBB at both September 30, 2023 and December 31, 2022 and 2% was not rated by Moody’s, S&P Global, or Fitch Ratings at both September 30, 2023 and December 31, 2022. 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 $17.1 million from the sale of debt securities resulted in an immaterial investment security gain for the three months ended September 30, 2023. Proceeds of $2.2 billion from the sale of debt securities resulted in investment security gains of $6.9 million for the nine months ended September 30, 2023. Proceeds of $100.2 million from the sale of debt securities resulted in an investment security loss of $0.3 million for the three and nine months ended September 30, 2022.

Loans

Loans	9 Months Ended
	Sep. 30, 2023
Receivables [Abstract]
Loans	Loans Amounts outstanding for Loans, by segment and class, are shown in the following table. TABLE 46: LOANS (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Commercial Commercial and Institutional (1) $ 12,061.3 $ 12,415.0 Commercial Real Estate 5,063.1 4,773.0 Non-U.S. (1) 2,857.8 3,131.1 Other 2,005.1 1,316.5 Total Commercial 21,987.3 21,635.6 Personal Private Client 14,068.6 14,119.0 Residential Real Estate 6,285.8 6,413.5 Non-U.S. 432.6 510.0 Other 802.7 215.2 Total Personal 21,589.7 21,257.7 Total Loans $ 43,577.0 $ 42,893.3 (1) Commercial and institutional and commercial-non-U.S. combined include $4.8 billion and $5.6 billion of private equity capital call finance loans at September 30, 2023 and December 31, 2022, 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 September 30, 2023 and December 31, 2022, equity credit lines totaled $228.1 million and $248.6 million, respectively, and equity credit lines for which first liens were held by Northern Trust represented 97% and 98% of the total equity credit lines as of September 30, 2023 and December 31, 2022, 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 $4.2 billion and $2.9 billion at September 30, 2023 and December 31, 2022, respectively. Demand deposit overdrafts reclassified as loan balances, primarily in personal-other, totaled $4.5 million and $24.4 million at September 30, 2023 and December 31, 2022, respectively. There were no loans classified as held for sale at September 30, 2023 or December 31, 2022. Loans classified as held for sale are recorded at the lower of cost or fair value. There were no loans sold for the three and nine months ended September 30, 2023, respectively, and no loans sold for the three months ended September 30, 2022. There were $11.2 million loans sold for the nine months ended September 30, 2022, which were comprised of residential real estate and commercial and institutional loans. Credit Quality Indicators. Credit quality indicators are statistics, measurements or other metrics that provide information regarding the relative credit risk of loans. Northern Trust utilizes 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 the 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 September 30, 2023 and December 31, 2022 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 47: CREDIT QUALITY INDICATOR AT AMORTIZED COST BASIS BY ORIGINATION YEAR September 30, 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 $ 355.1 $ 539.8 $ 874.3 $ 95.9 $ 148.3 $ 417.6 $ 5,148.5 $ 16.0 $ 7,595.5 4 to 5 Category 689.9 818.7 669.7 147.6 125.0 180.4 1,549.0 75.3 4,255.6 6 to 9 Category 13.9 71.1 69.3 12.2 0.1 1.7 41.5 0.4 210.2 Total Commercial and Institutional 1,058.9 1,429.6 1,613.3 255.7 273.4 599.7 6,739.0 91.7 12,061.3 Commercial Real Estate Risk Rating: 1 to 3 Category 334.2 331.8 183.5 19.1 40.8 45.9 47.7 0.5 1,003.5 4 to 5 Category 1,360.9 1,260.2 541.7 228.7 254.9 136.7 202.7 7.4 3,993.2 6 to 9 Category 16.2 3.3 21.6 — 8.2 14.6 2.5 — 66.4 Total Commercial Real Estate 1,711.3 1,595.3 746.8 247.8 303.9 197.2 252.9 7.9 5,063.1 Commercial Real Estate Gross Charge-offs — (4.5) — — — — — — (4.5) Non-U.S. Risk Rating: 1 to 3 Category 842.6 — 43.9 65.4 35.8 3.2 823.5 — 1,814.4 4 to 5 Category 689.6 0.8 — — 23.1 180.2 88.7 — 982.4 6 to 9 Category 46.5 14.5 — — — — — — 61.0 Total Non-U.S. 1,578.7 15.3 43.9 65.4 58.9 183.4 912.2 — 2,857.8 Other Risk Rating: 1 to 3 Category 1,190.9 — — — — — — — 1,190.9 4 to 5 Category 814.2 — — — — — — — 814.2 Total Other 2,005.1 — — — — — — — 2,005.1 Total Commercial 6,354.0 3,040.2 2,404.0 568.9 636.2 980.3 7,904.1 99.6 21,987.3 Commercial Gross Charge-offs — (4.5) — — — — — — (4.5) Personal Private Client Risk Rating: 1 to 3 Category 326.5 218.2 44.4 70.0 15.1 25.0 5,723.2 172.8 6,595.2 4 to 5 Category 305.3 467.8 686.6 99.9 155.4 165.7 5,115.6 429.5 7,425.8 6 to 9 Category 18.3 4.4 — — — 17.8 7.1 — 47.6 Total Private Client 650.1 690.4 731.0 169.9 170.5 208.5 10,845.9 602.3 14,068.6 Residential Real Estate Risk Rating: 1 to 3 Category 198.7 536.2 565.4 405.1 154.2 729.2 229.2 — 2,818.0 4 to 5 Category 115.1 644.7 682.6 672.1 273.7 863.7 142.9 — 3,394.8 6 to 9 Category — 17.5 5.5 2.2 11.0 33.8 3.0 — 73.0 Total Residential Real Estate 313.8 1,198.4 1,253.5 1,079.4 438.9 1,626.7 375.1 — 6,285.8 Residential Real Estate Gross Write-offs (0.8) — — — — (0.3) — — (1.1) Non-U.S. Risk Rating: 1 to 3 Category 16.1 3.7 0.6 — — 5.5 54.0 — 79.9 4 to 5 Category 9.0 20.7 39.4 — 18.8 8.3 249.0 7.5 352.7 Total Non-U.S. 25.1 24.4 40.0 — 18.8 13.8 303.0 7.5 432.6 Other Risk Rating: 1 to 3 Category 90.5 — — — — — — — 90.5 4 to 5 Category 712.2 — — — — — — — 712.2 Total Other 802.7 — — — — — — — 802.7 Total Personal 1,791.7 1,913.2 2,024.5 1,249.3 628.2 1,849.0 11,524.0 609.8 21,589.7 Personal Gross Charge-offs (0.8) — — — — (0.3) — — (1.1) Total Loans $ 8,145.7 $ 4,953.4 $ 4,428.5 $ 1,818.2 $ 1,264.4 $ 2,829.3 $ 19,428.1 $ 709.4 $ 43,577.0 Total Loans Gross Charge-offs $ (0.8) $ (4.5) $ — $ — $ — $ (0.3) $ — $ — $ (5.6) December 31, 2022 TERM LOANS REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2022 2021 2020 2019 2018 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 753.3 $ 1,087.5 $ 209.8 $ 159.3 $ 45.9 $ 511.3 $ 6,032.8 $ 17.7 $ 8,817.6 4 to 5 Category 744.1 740.6 300.8 191.1 151.4 174.7 1,102.3 32.9 3,437.9 6 to 9 Category 50.8 30.5 — 13.7 — — 64.5 — 159.5 Total Commercial and Institutional 1,548.2 1,858.6 510.6 364.1 197.3 686.0 7,199.6 50.6 12,415.0 Commercial Real Estate Risk Rating: 1 to 3 Category 318.7 227.4 123.6 123.5 39.8 39.1 113.4 3.0 988.5 4 to 5 Category 968.5 1,040.0 637.8 447.3 153.0 256.9 181.5 17.5 3,702.5 6 to 9 Category 7.7 22.7 — 49.1 — — 2.5 — 82.0 Total Commercial Real Estate 1,294.9 1,290.1 761.4 619.9 192.8 296.0 297.4 20.5 4,773.0 Non-U.S. Risk Rating: 1 to 3 Category 991.9 46.2 109.6 14.8 — 6.5 1,158.3 — 2,327.3 4 to 5 Category 459.0 — — — — 214.9 89.5 1.8 765.2 6 to 9 Category 0.1 — — 23.1 — — 15.4 — 38.6 Total Non-U.S. 1,451.0 46.2 109.6 37.9 — 221.4 1,263.2 1.8 3,131.1 Other Risk Rating: 1 to 3 Category 993.9 — — — — — — — 993.9 4 to 5 Category 322.6 — — — — — — — 322.6 Total Other 1,316.5 — — — — — — — 1,316.5 Total Commercial 5,610.6 3,194.9 1,381.6 1,021.9 390.1 1,203.4 8,760.2 72.9 21,635.6 Personal Private Client Risk Rating: 1 to 3 Category 395.5 159.9 50.5 313.6 13.4 18.5 5,352.5 28.2 6,332.1 4 to 5 Category 430.3 755.1 192.4 191.3 38.7 160.0 5,728.6 267.2 7,763.6 6 to 9 Category 0.9 — 0.1 — 18.6 — 3.7 — 23.3 Total Private Client 826.7 915.0 243.0 504.9 70.7 178.5 11,084.8 295.4 14,119.0 Residential Real Estate Risk Rating: 1 to 3 Category 871.6 666.7 567.7 168.1 102.9 750.8 128.4 7.9 3,264.1 4 to 5 Category 354.3 656.7 597.6 290.0 170.9 838.2 180.4 1.0 3,089.1 6 to 9 Category — 6.8 1.5 1.1 3.7 35.9 11.3 — 60.3 Total Residential Real Estate 1,225.9 1,330.2 1,166.8 459.2 277.5 1,624.9 320.1 8.9 6,413.5 Non-U.S. Risk Rating: 1 to 3 Category 3.0 3.7 — — 4.6 2.3 124.6 — 138.2 4 to 5 Category 24.2 40.3 — 21.3 3.2 2.9 272.0 7.8 371.7 6 to 9 Category — — — — — 0.1 — — 0.1 Total Non-U.S. 27.2 44.0 — 21.3 7.8 5.3 396.6 7.8 510.0 Other Risk Rating: 1 to 3 Category 190.8 — — — — — — — 190.8 4 to 5 Category 24.4 — — — — — — — 24.4 Total Other 215.2 — — — — — — — 215.2 Total Personal 2,295.0 2,289.2 1,409.8 985.4 356.0 1,808.7 11,801.5 312.1 21,257.7 Total Loans $ 7,905.6 $ 5,484.1 $ 2,791.4 $ 2,007.3 $ 746.1 $ 3,012.1 $ 20,561.7 $ 385.0 $ 42,893.3 Loans in the “1 to 3” category are expected to exhibit minimal to modest probabilities of default and are characterized by borrowers having the strongest financial qualities, including above average financial flexibility, cash flows and capital levels. Borrowers assigned these ratings are anticipated to experience very little to moderate financial pressure in adverse down-cycle scenarios. As a result of these characteristics, borrowers within this category exhibit a minimal to modest likelihood of loss. Loans in the “4 to 5” category are expected to exhibit moderate to acceptable probabilities of default and are characterized by borrowers with less financial flexibility than those in the “1 to 3” category. Cash flows and capital levels are generally sufficient to allow for borrowers to meet current requirements, but have fewer financial resources to manage through economic downturns. As a result of these characteristics, borrowers within this category exhibit a moderate likelihood of loss. Loans in the watch list category have elevated credit risk profiles that are monitored through internal watch lists, and consist of credits with borrower ratings of “6 to 9.” These credits, which include all nonaccrual credits, are expected to exhibit probabilities of default, elevated risk of default, or are currently in default. Borrowers associated with these risk profiles that are not currently in default have limited financial flexibility. Cash flows and capital levels range from acceptable to potentially insufficient to meet current requirements, particularly in adverse down cycle scenarios. As a result of these characteristics, borrowers in this category exhibit an elevated to probable likelihood of loss. 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 September 30, 2023 and December 31, 2022. TABLE 48: DELINQUENCY STATUS ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS September 30, 2023 Commercial Commercial and Institutional $ 12,032.4 $ 7.9 $ 1.6 $ 3.1 $ 12,045.0 $ 16.3 $ 12,061.3 $ 6.9 Commercial Real Estate 5,059.9 — — — 5,059.9 3.2 5,063.1 3.2 Non-U.S. 2,854.8 3.0 — — 2,857.8 — 2,857.8 — Other 2,005.1 — — — 2,005.1 — 2,005.1 — Total Commercial 21,952.2 10.9 1.6 3.1 21,967.8 19.5 21,987.3 10.1 Personal Private Client 13,911.3 91.0 13.4 33.1 14,048.8 19.8 14,068.6 17.8 Residential Real Estate 6,254.9 — 1.4 — 6,256.3 29.5 6,285.8 28.1 Non-U.S. 432.6 — — — 432.6 — 432.6 — Other 802.7 — — — 802.7 — 802.7 — Total Personal 21,401.5 91.0 14.8 33.1 21,540.4 49.3 21,589.7 45.9 Total Loans $ 43,353.7 $ 101.9 $ 16.4 $ 36.2 $ 43,508.2 $ 68.8 $ 43,577.0 $ 56.0 Other Real Estate Owned $ 0.3 Total Nonaccrual Assets $ 69.1 ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS December 31, 2022 Commercial Commercial and Institutional $ 12,353.7 $ 40.2 $ 3.0 $ 0.7 $ 12,397.6 $ 17.4 $ 12,415.0 $ 4.4 Commercial Real Estate 4,761.5 1.3 — — 4,762.8 10.2 4,773.0 6.2 Non-U.S. 3,131.1 — — — 3,131.1 — 3,131.1 — Other 1,316.5 — — — 1,316.5 — 1,316.5 — Total Commercial 21,562.8 41.5 3.0 0.7 21,608.0 27.6 21,635.6 10.6 Personal Private Client 13,843.5 192.3 29.9 53.3 14,119.0 — 14,119.0 — Residential Real Estate 6,373.2 9.6 12.3 0.1 6,395.2 18.3 6,413.5 18.3 Non-U.S 509.9 — — 0.1 510.0 — 510.0 — Other 215.2 — — — 215.2 — 215.2 — Total Personal 20,941.8 201.9 42.2 53.5 21,239.4 18.3 21,257.7 18.3 Total Loans $ 42,504.6 $ 243.4 $ 45.2 $ 54.2 $ 42,847.4 $ 45.9 $ 42,893.3 $ 28.9 Other Real Estate Owned $ — Total Nonaccrual Assets $ 45.9 Interest income that would have been recorded for nonaccrual loans in accordance with their original terms was $0.9 million and $2.3 million for the three and nine months ended September 30, 2023, respectively, and $1.1 million and $3.2 million for the three and nine months ended September 30, 2022, respectively. Northern Trust may obtain physical possession of real estate via foreclosure on an in-substance repossession. As of September 30, 2023 and December 31, 2022, Northern Trust held foreclosed real estate properties with an immaterial carrying value, as a result of obtaining physical possession. In addition, as of both September 30, 2023 and December 31, 2022, Northern Trust had loans with a carrying value of $1.1 million, for which formal foreclosure proceedings were in process. Loan Modifications to Borrowers Experiencing Financial Difficulty (After the Adoption of Accounting Standards Update No. 2022-02) 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 the 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 September 30, 2023, disaggregated by relevant class of financing receivable and type of modification provided. TABLE 49: LOAN MODIFICATIONS MADE TO BORROWERS EXPERIENCING FINANCIAL DIFFICULTY THREE MONTHS ENDED SEPTEMBER 30, 2023 NINE MONTHS ENDED SEPTEMBER 30, 2023 (in $ million) LOAN MODIFICATION DETAIL AMORTIZED COST BASIS % OF TOTAL SEGMENT AMORTIZED COST BASIS % OF TOTAL SEGMENT Commercial Commercial and Institutional Extension of term $ 16.7 0.14 % $ 16.7 0.14 % Commercial Real Estate Combination of principal and/or interest deferral and extension of term — — — (1) — Total Commercial 16.7 0.08 16.7 0.08 Personal Residential Real Estate Principal and/or interest deferral 0.1 — 3.2 0.05 Residential Real Estate Combination of principal and/or interest deferral and extension of term 4.7 0.08 4.7 0.08 Private Client Extension of term — — — (1) — Total Personal 4.8 0.02 7.9 0.04 Total Loans $ 21.5 0.05 % $ 24.6 0.06 % (1) Included are financially distressed modifications of $32.5 million (combinations of principal and/or interest deferral and term extensions) for the commercial real estate portfolio and $0.2 million (term extensions) for the private client portfolio for which the respective loans had no amortized cost basis as of the end of the respective period. The $32.5 million loan was fully repaid during the second quarter of 2023. The following table describes the financial effect of the modifications made to borrowers experiencing financial difficulty. TABLE 50: FINANCIAL EFFECT OF MODIFICATIONS MADE TO BORROWERS EXPERIENCING FINANCIAL DIFFICULTY THREE MONTHS ENDED SEPTEMBER 30, 2023 NINE MONTHS ENDED SEPTEMBER 30, 2023 FINANCIAL EFFECT FINANCIAL EFFECT PRINCIPAL AND INTEREST DEFERRAL Commercial Commercial Real Estate — Northern Trust provided a weighted average of 6 months payment deferrals to borrowers for total deferred principal and interest of $32.5 million. Personal Residential Real Estate Northern Trust provided a weighted average of 9 months payment deferrals to borrowers for immaterial principal and interest deferral amounts. Northern Trust provided a weighted average of 9 months payment deferrals to borrowers for immaterial principal and interest deferral amounts. TERM EXTENSION Commercial Commercial and Institutional Northern Trust provided weighted average term extensions of 12 months. Northern Trust provided weighted average term extensions of 12 months. Commercial Real Estate — Northern Trust provided weighted average term extensions of 6 months. Personal Residential Real Estate Northern Trust provided weighted average term extensions of 9 months. Northern Trust provided weighted average term extensions of 9 months. Private Client — Northern Trust provided weighted average term extensions of 60 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. All of the loans that were modified since the adoption of ASU 2022-02 as of January 1, 2023, were performing in accordance with their modified terms and were not considered past due for purposes of these disclosures as of September 30, 2023. During the current period, Northern Trust did not recognize any charge-offs related to modifications to borrowers experiencing financial difficulty that had been processed since the adoption of ASU 2022-02. For the nine months ended September 30, 2023, Northern Trust charged off $0.7 million related to these modifications. 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 September 30, 2023. 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. Troubled Debt Restructurings (Prior to the Adoption of Accounting Standards Update No. 2022-02) Prior to January 1, 2023, a loan that has been modified as a concession by Northern Trust or a bankruptcy court resulting from the debtor’s financial difficulties is referred to as a troubled debt restructuring (TDR). All TDRs are reported starting in the calendar year of their restructuring. In subsequent years, a TDR may cease being reported if the loan was modified at a market rate and has performed according to the modified terms for at least six payment periods. A loan that has been modified at a below market rate will return to accrual status if it satisfies the six-payment-period performance requirement. The expected credit loss is measured based upon the present value of expected future cash flows, discounted at the effective interest rate based on the original 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. Smaller balance (individually less than $1 million) homogeneous loans are collectively evaluated. Northern Trust’s accounting policies for material nonaccrual loans is consistent across all classes of loans. All loans with TDR modifications are evaluated for additional expected credit losses. 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. Included within nonaccrual loans were $35.3 million of nonaccrual TDRs, and $39.7 million of accrual TDRs as of December 31, 2022 . There were $0.2 million of aggregate undrawn loan commitments and standby letters of credit at December 31, 2022, issued to borrowers with TDR modifications of loans. TDR modifications involve extensions of term, deferrals of principal, interest rate concessions, and other modifications. Other modifications typically reflect other nonstandard terms which Northern Trust would not offer in non-troubled situations. The following table provides, by segment and class, the number of TDR modifications of loans entered into during the three and nine months ended September 30, 2022, and the recorded investments and unpaid principal balances as of September 30, 2022. TABLE 51: TROUBLED DEBT RESTRUCTURINGS THREE MONTHS ENDED SEPTEMBER 30, 2022 NINE MONTHS ENDED SEPTEMBER 30, 2022 ($ In Millions) LOAN MODIFICATION DETAIL NUMBER OF RECORDED UNPAID NUMBER OF RECORDED UNPAID Commercial Commercial and Institutional Interest rate concession, extension of term and other modification 1 $ 0.1 $ 0.1 2 $ 0.6 $ 0.6 Commercial Real Estate Interest rate concession and other modification 1 31.6 32.5 1 31.6 32.5 Total Commercial 2 31.7 32.6 3 32.2 33.1 Personal Residential Real Estate Interest rate concession, deferrals of principal, extension of term and other modification 1 0.1 0.1 3 0.2 0.2 Total Personal 1 0.1 0.1 3 0.2 0.2 Total Loans and Leases 3 $ 31.8 $ 32.7 6 $ 32.4 $ 33.3 Note: Period-end balances reflect all pay downs and charge-offs during the year.

Allowance for Credit Losses

Allowance for Credit Losses	9 Months Ended
	Sep. 30, 2023
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, many of which are interrelated or dependent on other assumptions and estimates, 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 Credit Risk Management, Treasury, Corporate Finance, the Economic Research Department, and each of Northern Trust’s reporting segments. 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 and nine months ended September 30, 2023 and 2022. TABLE 52: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES THREE MONTHS ENDED SEPTEMBER 30, 2023 (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 $ 152.5 $ 26.0 $ 16.7 $ 1.0 $ 196.2 Charge-Offs (0.8) — — — (0.8) Recoveries 1.1 — — — 1.1 Net Recoveries (Charge-Offs) 0.3 — — — 0.3 Provision for (Release of) Credit Losses (1) 14.0 2.3 (1.8) 0.1 14.6 Balance at End of Period $ 166.8 $ 28.3 $ 14.9 $ 1.1 $ 211.1 (1) The table excludes a release of credit reserves of $0.6 million for the three months ended September 30, 2023 for AFS debt securities. NINE MONTHS ENDED SEPTEMBER 30, 2023 (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 $ 144.3 $ 38.5 $ 16.0 $ 0.8 $ 199.6 Charge-Offs (5.6) — — — (5.6) Recoveries 3.0 — — — 3.0 Net Recoveries (Charge-Offs) (2.6) — — — (2.6) Provision for (Release of) Credit Losses (1) 25.1 (10.2) (1.1) 0.3 14.1 Balance at End of Period $ 166.8 $ 28.3 $ 14.9 $ 1.1 $ 211.1 (1) The table excludes a release of credit reserves of $0.6 million for the nine months ended September 30, 2023 for AFS debt securities. See further detail in Note 4—Securities. THREE MONTHS ENDED SEPTEMBER 30, 2022 (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 $ 138.2 $ 43.5 $ 15.4 $ 1.1 $ 198.2 Charge-Offs (5.4) — — — (5.4) Recoveries 0.9 — — — 0.9 Net Recoveries (Charge-Offs) (4.5) — — — (4.5) Provision for (Release of) Credit Losses (1) 5.0 (2.8) (0.4) (0.4) 1.4 Balance at End of Period $ 138.7 $ 40.7 $ 15.0 $ 0.7 $ 195.1 (1) The table excludes a release of credit reserves of $0.9 million for the three months ended September 30, 2022 for AFS debt securities. See further detail in Note 4—Securities. NINE MONTHS ENDED SEPTEMBER 30, 2022 (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 $ 138.4 $ 34.1 $ 11.2 $ 1.0 $ 184.7 Charge-Offs (5.5) — — — (5.5) Recoveries 9.7 — — — 9.7 Net Recoveries (Charge-Offs) 4.2 — — — 4.2 Provision for (Release of) Credit Losses (1) (3.9) 6.6 3.8 (0.3) 6.2 Balance at End of Period $ 138.7 $ 40.7 $ 15.0 $ 0.7 $ 195.1 (1) The table excludes a provision for credit losses of $0.8 million for the nine months ended September 30, 2022 for AFS debt securities. See further detail in Note 4—Securities. The Provision for Credit Losses, excluding the release of credit reserves for available for sale debt securities, was $14.6 million in the current quarter, as compared to a $1.4 million provision in the prior-year quarter. The provision was primarily due to an increase in the reserve evaluated on a collective basis, driven by a small number of large new loans and renewals and credit quality deterioration of certain commercial real estate (CRE) and commercial and institutional (C&I) loans, partially offset by a net improvement in the overall macroeconomic outlook. The reserve evaluated on a collective basis relates to pooled financial assets sharing similar risk characteristics. There were net recoveries of $0.3 million during the three months ended September 30, 2023, as compared to net charge-offs of $4.5 million for the three months ended September 30, 2022. For further detail, please see the Allowance for the Loan Portfolio and the Allowance for Held to Maturity Debt Securities Portfolio sections below. The Provision for Credit Losses, excluding the release of credit reserves for available for sale debt securities, was $14.1 million for the nine months ended September 30, 2023, as compared to a $6.2 million provision in the prior-year period. The provision was primarily due to an increase in the collective basis reserve, driven by new loans and renewals in the CRE portfolio and expectations of higher economic stress in the CRE market, particularly office CRE, partially offset by a net improvement in the overall macroeconomic outlook and lower loss projections for certain large C&I loans. The reserve evaluated on a collective basis relates to pooled financial assets sharing similar risk characteristics. There were net charge-offs of $2.6 million during the nine months ended September 30, 2023, as compared to net recoveries of $4.2 million during the nine months ended September 30, 2022. 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, and real estate price indices, as well as financial market factors such as equity prices, 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 continued slow but steady growth, with inflation, labor markets, and interest rates continuing to stabilize. 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 and nine months ended September 30, 2023 and 2022. TABLE 53: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO LOANS THREE MONTHS ENDED SEPTEMBER 30, 2023 LOANS UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 124.0 $ 28.5 $ 152.5 $ 23.3 $ 2.7 $ 26.0 Charge-Offs (0.5) (0.3) (0.8) — — — Recoveries — 1.1 1.1 — — — Net Recoveries (Charge-Offs) (0.5) 0.8 0.3 — — — Provision for (Release of) Credit Losses 13.9 0.1 14.0 2.2 0.1 2.3 Balance at End of Period $ 137.4 $ 29.4 $ 166.8 $ 25.5 $ 2.8 $ 28.3 NINE MONTHS ENDED SEPTEMBER 30, 2023 LOANS 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 (4.5) (1.1) (5.6) — — — Recoveries 0.1 2.9 3.0 — — — Net Recoveries (Charge-Offs) (4.4) 1.8 (2.6) — — — Provision for (Release of) Credit Losses 25.6 (0.5) 25.1 (10.8) 0.6 (10.2) Balance at End of Period $ 137.4 $ 29.4 $ 166.8 $ 25.5 $ 2.8 $ 28.3 THREE MONTHS ENDED SEPTEMBER 30, 2022 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 102.5 $ 35.7 $ 138.2 $ 40.3 $ 3.2 $ 43.5 Charge-Offs (4.9) (0.5) (5.4) — — — Recoveries 0.3 0.6 0.9 — — — Net Recoveries (Charge-Offs) (4.6) 0.1 (4.5) — — — Provision for (Release of) Credit Losses 2.7 2.3 5.0 (2.8) — (2.8) Balance at End of Period $ 100.6 $ 38.1 $ 138.7 $ 37.5 $ 3.2 $ 40.7 NINE MONTHS ENDED SEPTEMBER 30, 2022 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 105.6 $ 32.8 $ 138.4 $ 31.4 $ 2.7 $ 34.1 Charge-Offs (4.9) (0.6) (5.5) — — — Recoveries 2.7 7.0 9.7 — — — Net Recoveries (Charge-Offs) (2.2) 6.4 4.2 — — — Provision for (Release of) Credit Losses (2.8) (1.1) (3.9) 6.1 0.5 6.6 Balance at End of Period $ 100.6 $ 38.1 $ 138.7 $ 37.5 $ 3.2 $ 40.7 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 primarily based on internally developed loss data specific to the Northern Trust 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 homogenous 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 of the loan portfolio. Allowance Related to Credit Exposure Evaluated on an Individual Basis. The allowance is determined through an individual evaluation of loans, and lending-related commitments that have defaulted, generally those with borrower ratings of 8 and 9, that is 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 September 30, 2023 and December 31, 2022. TABLE 54: RECORDED INVESTMENTS IN LOANS SEPTEMBER 30, 2023 DECEMBER 31, 2022 (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Loans Evaluated on an Individual Basis $ 27.4 $ 67.3 $ 94.7 $ 63.0 $ 46.1 $ 109.1 Evaluated on a Collective Basis 21,959.9 21,522.4 43,482.3 21,572.6 21,211.6 42,784.2 Total Loans 21,987.3 21,589.7 43,577.0 21,635.6 21,257.7 42,893.3 Allowance for Credit Losses on Loans Evaluated on an Individual Basis 8.3 2.0 10.3 10.4 — 10.4 Evaluated on a Collective Basis 129.1 27.4 156.5 105.8 28.1 133.9 Allowance Assigned to Loans 137.4 29.4 166.8 116.2 28.1 144.3 Allowance for Undrawn Loan Commitments and Standby Letters of Credit Evaluated on an Individual Basis — — — — — — Evaluated on a Collective Basis 25.5 2.8 28.3 36.3 2.2 38.5 Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit 25.5 2.8 28.3 36.3 2.2 38.5 Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit $ 162.9 $ 32.2 $ 195.1 $ 152.5 $ 30.3 $ 182.8 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 and nine months ended September 30, 2023 and 2022. TABLE 55: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO HELD TO MATURITY DEBT SECURITIES THREE MONTHS ENDED SEPTEMBER 30, 2023 (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 $ 1.4 $ 5.4 $ 3.4 $ 1.3 $ 0.1 $ 5.1 $ 16.7 Provision for (Release of) Credit Losses (0.1) (0.8) (0.5) (0.1) — (0.3) (1.8) Balance at End of Period $ 1.3 $ 4.6 $ 2.9 $ 1.2 $ 0.1 $ 4.8 $ 14.9 (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. NINE MONTHS ENDED SEPTEMBER 30, 2023 (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 $ 1.9 $ 3.6 $ 4.0 $ 1.5 $ 0.1 $ 4.9 $ 16.0 Provision for (Release of) Credit Losses (0.6) 1.0 (1.1) (0.3) — (0.1) (1.1) Balance at End of Period $ 1.3 $ 4.6 $ 2.9 $ 1.2 $ 0.1 $ 4.8 $ 14.9 (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 SEPTEMBER 30, 2022 (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 $ 1.8 $ 3.8 $ 4.8 $ — $ 0.1 $ 4.9 $ 15.4 Provision for (Release of) Credit Losses (0.3) (0.7) (1.0) — — 1.6 (0.4) Balance at End of Period $ 1.5 $ 3.1 $ 3.8 $ — $ 0.1 $ 6.5 $ 15.0 NINE MONTHS ENDED SEPTEMBER 30, 2022 (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 $ 1.4 $ 1.9 $ 3.0 $ — $ 0.1 $ 4.8 $ 11.2 Provision for (Release of) Credit Losses 0.1 1.2 0.8 — — 1.7 3.8 Balance at End of Period $ 1.5 $ 3.1 $ 3.8 $ — $ 0.1 $ 6.5 $ 15.0 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” 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 $1.1 million and $0.8 million as of September 30, 2023 and December 31, 2022, 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 quarter 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 56: ACCRUED INTEREST (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Loans $ 249.4 $ 203.1 Debt Securities Held to Maturity 82.7 63.2 Available for Sale 138.0 147.1 Other Financial Assets 58.4 43.8 Total $ 528.5 $ 457.2 The amount of accrued interest reversed through interest income for loans was immaterial for the three and nine months ended September 30, 2023 and 2022, and there was no accrued interest reversed through interest income related to any other financial assets for the three and nine months ended September 30, 2023 and 2022.

Pledged Assets, Collateral and

Pledged Assets, Collateral and Restricted Assets	9 Months Ended
	Sep. 30, 2023
Transfers and Servicing [Abstract]
Pledged Assets, Collateral and Restricted Assets	Pledged Assets, 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 and borrowings and derivative settlements. The following table presents the carrying value of Northern Trust's pledged assets by type. TABLE 57: TYPE OF PLEDGED ASSETS (In Billions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Debt Securities (1) $ 27.8 $ 31.4 Loans (2) 11.2 11.8 Total Pledged Assets $ 39.0 $ 43.2 (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. Within pledged assets, there was collateral required which totaled $13.1 billion and $8.7 billion at September 30, 2023 and December 31, 2022, respectively. The following table presents the AFS debt securities pledged as collateral that are included in pledged assets. TABLE 58: FAIR VALUE OF AVAILABLE FOR SALE DEBT SECURITIES INCLUDED IN PLEDGED ASSETS SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE DERIVATIVE CONTRACTS (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 SEPTEMBER 30, 2023 DECEMBER 31, 2022 Debt Securities Available for Sale $ 540.7 $ 464.7 $ 15.6 $ 34.7 The secured parties to these transactions have the right to repledge or sell the securities as it relates to $540.7 million and $464.7 million of the pledged collateral as of September 30, 2023 and December 31, 2022, respectively. 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 59: ACCEPTED COLLATERAL (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Collateral that may be repledged or sold Reverse repurchase agreements (1)(2) $ 49,972.7 $ 12,119.4 Derivative contracts 14.3 5.0 Collateral that may not be repledged or sold Reverse repurchase agreements — 450.0 Total Collateral Accepted $ 49,987.0 $ 12,574.4 (1) The fair value of securities collateral that was repledged or sold totaled $49.6 billion and $11.5 billion at September 30, 2023 and December 31, 2022, 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 September 30, 2023 and December 31, 2022, these balances totaled $642.8 million and $330.4 million, respectively, and are reported in Cash and Due from Banks on the consolidated balance sheets. At September 30, 2023 and December 31, 2022, Northern Trust held cash of $553.6 million and $574.2 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 and nine months ended September 30, 2023 and 2022.

Goodwill and Other Intangibles

Goodwill and Other Intangibles	9 Months Ended
	Sep. 30, 2023
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 nine months ended September 30, 2023, including the effect of foreign exchange rates on non-U.S. dollar denominated balances, were as follows. TABLE 60: GOODWILL (In Millions) ASSET WEALTH MANAGEMENT TOTAL Balance at December 31, 2022 $ 611.0 $ 80.3 $ 691.3 Foreign Exchange Rates 1.5 — 1.5 Balance at September 30, 2023 $ 612.5 $ 80.3 $ 692.8 Other Intangible Assets Subject to Amortization . The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of September 30, 2023 and December 31, 2022 were as follows. TABLE 61: OTHER INTANGIBLE ASSETS (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Gross Carrying Amount $ 128.7 $ 197.9 Less: Accumulated Amortization 58.4 120.3 Net Book Value $ 70.3 $ 77.6 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 and $7.0 million for the three and nine months ended September 30, 2023, respectively and $2.2 million and $7.1 million for the three and nine months ended September 30, 2022, respectively. Amortization for the remainder of 2023 and for the years 2024, 2025, 2026, and 2027 is estimated to be $2.3 million, $9.0 million, $8.5 million, $8.1 million, and $7.9 million, respectively. Capitalized Software. The gross carrying amount and accumulated amortization of capitalized software as of September 30, 2023 and December 31, 2022 were as follows. TABLE 62: CAPITALIZED SOFTWARE (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Gross Carrying Amount $ 3,896.1 $ 3,479.3 Less: Accumulated Amortization 1,881.6 1,517.4 Net Book Value $ 2,014.5 $ 1,961.9 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 $126.7 million and $370.8 million for the three and nine months ended September 30, 2023, respectively, and $111.1 million and $317.0 million for the three and nine months ended September 30, 2022, respectively.

Reporting Segments

Reporting Segments	9 Months Ended
	Sep. 30, 2023
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 fully taxable equivalent (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 costs associated with acquisitions, divestitures, litigation, restructuring, and tax adjustments not directly attributable to a specific reporting segment. 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- and nine-month periods ended September 30, 2023 and 2022. TABLE 63: RESULTS OF REPORTING SEGMENTS ($ In Millions) ASSET SERVICING WEALTH MANAGEMENT OTHER RECONCILING ITEMS TOTAL CONSOLIDATED THREE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 2023 2022 2023 2022 2023 2022 Noninterest Income Trust, Investment and Other Servicing Fees $ 626.0 $ 603.2 $ 485.9 $ 475.5 $ — $ — $ — $ — $ 1,111.9 $ 1,078.7 Foreign Exchange Trading Income (Loss) 54.3 63.7 (2.5) 1.0 — — — — 51.8 64.7 Other Noninterest Income (Loss) 66.1 62.5 38.1 37.0 2.4 (1.1) — — 106.6 98.4 Total Noninterest Income (Loss) 746.4 729.4 521.5 513.5 2.4 (1.1) — — 1,270.3 1,241.8 Net Interest Income 281.2 303.3 188.2 222.0 — — (13.2) (12.3) 456.2 513.0 Revenue 1,027.6 1,032.7 709.7 735.5 2.4 (1.1) (13.2) (12.3) 1,726.5 1,754.8 Provision for (Release of) Credit Losses 3.1 (5.1) 10.9 5.6 — — — — 14.0 0.5 Noninterest Expense 809.3 760.4 456.9 449.0 12.0 20.4 — — 1,278.2 1,229.8 Income before Income Taxes 215.2 277.4 241.9 280.9 (9.6) (21.5) (13.2) (12.3) 434.3 524.5 Provision for Income Taxes 54.3 67.7 67.7 79.6 (2.3) (5.3) (13.2) (12.3) 106.5 129.7 Net Income $ 160.9 $ 209.7 $ 174.2 $ 201.3 $ (7.3) $ (16.2) $ — $ — $ 327.8 $ 394.8 Percentage of Consolidated Net Income 49 % 53 % 53 % 51 % (2) % (4) % N/A N/A 100 % 100 % Average Assets $ 108,656.7 $ 109,677.2 $ 31,544.9 $ 36,725.0 $ — $ — N/A N/A $ 140,201.6 $ 146,402.2 ($ In Millions) ASSET SERVICING WEALTH MANAGEMENT OTHER RECONCILING ITEMS TOTAL CONSOLIDATED NINE MONTHS ENDED 2023 2022 2023 2022 2023 2022 2023 2022 2023 2022 Noninterest Income Trust, Investment and Other Servicing Fees $ 1,850.2 $ 1,908.4 $ 1,421.6 $ 1,482.1 $ — $ — $ — $ — $ 3,271.8 $ 3,390.5 Foreign Exchange Trading Income (Loss) 161.2 215.9 (6.3) 7.3 — — — — 154.9 223.2 Other Noninterest Income (Loss) 199.0 185.4 112.8 101.6 (9.2) (11.2) — — 302.6 275.8 Total Noninterest Income (Loss) 2,210.4 2,309.7 1,528.1 1,591.0 (9.2) (11.2) — — 3,729.3 3,889.5 Net Interest Income 902.6 748.5 635.8 634.3 — — (39.5) (30.1) 1,498.9 1,352.7 Revenue 3,113.0 3,058.2 2,163.9 2,225.3 (9.2) (11.2) (39.5) (30.1) 5,228.2 5,242.2 Provision for (Release of) Credit Losses (3.3) 3.8 16.8 3.2 — — — — 13.5 7.0 Noninterest Expense 2,459.7 2,269.4 1,402.4 1,333.2 33.6 56.7 — — 3,895.7 3,659.3 Income before Income Taxes 656.6 785.0 744.7 888.9 (42.8) (67.9) (39.5) (30.1) 1,319.0 1,575.9 Provision for Income Taxes 167.4 194.0 207.5 248.6 (10.6) (16.9) (39.5) (30.1) 324.8 395.6 Net Income $ 489.2 $ 591.0 $ 537.2 $ 640.3 $ (32.2) $ (51.0) $ — $ — $ 994.2 $ 1,180.3 Percentage of Consolidated Net Income 49 % 50 % 54 % 54 % (3) % (4) % N/A N/A 100 % 100 % Average Assets $ 110,380.4 $ 117,251.0 $ 34,311.2 $ 36,901.1 $ — $ — N/A N/A $ 144,691.6 $ 154,152.1 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	9 Months Ended
	Sep. 30, 2023
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock. The Corporation is authorized to issue 10.0 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 September 30, 2023, 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 September 30, 2023, 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 September 30, 2023 and December 31, 2022 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 July 18, 2023, the Corporation declared a cash dividend of $2,300.00 per share of Series D Preferred Stock payable on October 1, 2023, to stockholders of record as of September 15, 2023. Series E Preferred Stock. As of September 30, 2023, the Corporation had issued and outstanding 16.0 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 September 30, 2023 and December 31, 2022 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 July 18, 2023, the Corporation declared a cash dividend of $293.75 per share of Series E Preferred Stock payable on October 1, 2023, to stockholders of record as of September 15, 2023. Common Stock. The Corporation’s current stock repurchase authorization to repurchase up to 25.0 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 and nine months ended September 30, 2023, the Corporation repurchased 14,738 and 2,426,793 shares of common stock, respectively, at a total cost of $1.1 million ($77.39 average price per share) and $201.3 million ($82.95 average price per share), respectively, including 14,738 and 356,145 shares, respectively, withheld to satisfy tax withholding obligations related to share-based compensation. For the three and nine months ended September 30, 2022, the Corporation repurchased 11,080 and 309,334 shares of common stock, respectively, at a total cost of $1.2 million ($96.43 average price per share) and $35.2 million ($113.89 average prices per share), respectively, all of which were shares withheld to satisfy tax withholding obligations related to share-based compensation.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and 2022, and changes during the three and nine months then ended. TABLE 64: SUMMARY OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED SEPTEMBER 30, 2023 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES (1) NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at June 30, 2023 $ (1,229.4) $ 0.5 $ 189.2 $ (366.2) $ (1,405.9) Net Change 32.3 (0.4) 9.6 1.0 42.5 Balance at September 30, 2023 $ (1,197.1) $ 0.1 $ 198.8 $ (365.2) $ (1,363.4) (1) Includes net unrealized gains (losses) on debt securities transferred from AFS to HTM. Refer to Note 4—Securities for further information. NINE MONTHS ENDED SEPTEMBER 30, 2023 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES (1) 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 170.5 (1.1) 34.2 2.2 205.8 Balance at September 30, 2023 $ (1,197.1) $ 0.1 $ 198.8 $ (365.2) $ (1,363.4) (1) Includes net unrealized gains (losses) on debt securities transferred from AFS to HTM. Refer to Note 4—Securities for further information. THREE MONTHS ENDED SEPTEMBER 30, 2022 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES (1) NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at June 30, 2022 $ (1,294.7) $ 0.6 $ 137.6 $ (354.1) $ (1,510.6) Net Change (272.2) 2.1 20.2 (24.5) (274.4) Balance at September 30, 2022 $ (1,566.9) $ 2.7 $ 157.8 $ (378.6) $ (1,785.0) (1) Includes net unrealized gains (losses) on debt securities transferred from AFS to HTM. Refer to Note 4—Securities for further information. NINE MONTHS ENDED SEPTEMBER 30, 2022 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES (1) NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2021 $ 107.1 $ (2.4) $ 155.2 $ (295.5) $ (35.6) Net Change (1,674.0) 5.1 2.6 (83.1) (1,749.4) Balance at September 30, 2022 $ (1,566.9) $ 2.7 $ 157.8 $ (378.6) $ (1,785.0) (1) Includes net unrealized gains (losses) on debt securities transferred from AFS to HTM. Refer to Note 4—Securities for further information. TABLE 65: DETAILS OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED SEPTEMBER 30, 2023 2022 (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 $ 18.0 $ (5.6) $ 12.4 $ (385.6) $ 97.5 $ (288.1) Reclassification Adjustments for (Gains) Losses Included in Net Income: Interest Income on Debt Securities (1) 26.7 (6.8) 19.9 21.0 (5.3) 15.7 Net (Gains) Losses on Debt Securities (2) — — — 0.3 (0.1) 0.2 Net Change $ 44.7 $ (12.4) $ 32.3 $ (364.3) $ 92.1 $ (272.2) Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ 14.3 $ (3.6) $ 10.7 $ 2.2 $ (0.6) $ 1.6 Reclassification Adjustment for (Gains) Losses Included in Net Income (3) (14.9) 3.8 (11.1) 0.6 (0.1) 0.5 Net Change $ (0.6) $ 0.2 $ (0.4) $ 2.8 $ (0.7) $ 2.1 Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (89.2) $ 1.7 $ (87.5) $ (168.1) $ 3.9 $ (164.2) Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) (0.2) 0.1 (0.1) (2.0) 0.5 (1.5) Net Investment Hedge Gains (Losses) 129.9 (32.7) 97.2 248.4 (62.5) 185.9 Net Change $ 40.5 $ (30.9) $ 9.6 $ 78.3 $ (58.1) $ 20.2 Pension and Other Postretirement Benefit Adjustments Net Actuarial Gains (Losses) $ (0.2) $ — $ (0.2) $ (51.6) $ 13.0 $ (38.6) Reclassification Adjustment for (Gains) Losses Included in Net Income (4) Amortization of Net Actuarial Loss 1.6 (0.4) 1.2 1.9 (0.4) 1.5 Amortization of Prior Service Cost (Credit) — — — (0.2) 0.1 (0.1) Settlement Loss — — — 17.0 (4.3) 12.7 Net Change $ 1.4 $ (0.4) $ 1.0 $ (32.9) $ 8.4 $ (24.5) Total Net Change $ 86.0 $ (43.5) $ 42.5 $ (316.1) $ 41.7 $ (274.4) NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 (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 $ 158.6 $ (42.0) $ 116.6 $ (2,288.3) $ 587.4 $ (1,700.9) Reclassification Adjustments for (Gains) Losses Included in Net Income: Interest Income on Debt Securities (1) 79.0 (19.9) 59.1 35.7 (9.0) 26.7 Net (Gains) Losses on Debt Securities (2) (6.9) 1.7 (5.2) 0.3 (0.1) 0.2 Net Change $ 230.7 $ (60.2) $ 170.5 $ (2,252.3) $ 578.3 $ (1,674.0) Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ 16.2 $ (4.1) $ 12.1 $ 3.0 $ (0.8) $ 2.2 Reclassification Adjustment for (Gains) Losses Included in Net Income (3) (17.7) 4.5 (13.2) 3.8 (0.9) 2.9 Net Change $ (1.5) $ 0.4 $ (1.1) $ 6.8 $ (1.7) $ 5.1 Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (15.7) $ 1.2 $ (14.5) $ (382.1) $ 4.5 $ (377.6) Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) (1.8) 0.5 (1.3) (3.8) 1.0 (2.8) Net Investment Hedge Gains (Losses) 66.8 (16.8) 50.0 512.1 (129.1) 383.0 Net Change $ 49.3 $ (15.1) $ 34.2 $ 126.2 $ (123.6) $ 2.6 Pension and Other Postretirement Benefit Adjustments Net Actuarial Gains (Losses) $ (1.5) $ 0.1 $ (1.4) $ (165.2) $ 41.2 $ (124.0) Reclassification Adjustment for (Gains) Losses Included in Net Income (4) Amortization of Net Actuarial Loss 4.8 (1.2) 3.6 17.1 (4.2) 12.9 Amortization of Prior Service Cost (Credit) — — — (0.7) 0.2 (0.5) Settlement Loss — — — 38.0 (9.5) 28.5 Net Change $ 3.3 $ (1.1) $ 2.2 $ (110.8) $ 27.7 $ (83.1) Total Net Change $ 281.8 $ (76.0) $ 205.8 $ (2,230.1) $ 480.7 $ (1,749.4) (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. Refer to Note 4—Securities for further information. (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	9 Months Ended
	Sep. 30, 2023
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 66: NET INCOME PER COMMON SHARE THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, ($ In Millions Except Per Common Share Information) 2023 2022 2023 2022 Basic Net Income Per Common Share Average Number of Common Shares Outstanding 207,021,554 208,400,135 207,611,420 208,271,070 Net Income $ 327.8 $ 394.8 $ 994.2 $ 1,180.3 Less: Dividends on Preferred Stock 16.2 16.2 37.1 37.1 Net Income Applicable to Common Stock 311.6 378.6 957.1 1,143.2 Less: Earnings Allocated to Participating Securities 3.1 3.2 9.7 9.5 Earnings Allocated to Common Shares Outstanding 308.5 375.4 947.4 1,133.7 Basic Net Income Per Common Share $ 1.49 $ 1.80 $ 4.56 $ 5.44 Diluted Net Income Per Common Share Average Number of Common Shares Outstanding 207,021,554 208,400,135 207,611,420 208,271,070 Plus: Dilutive Effect of Share-based Compensation 231,438 488,437 316,300 587,906 Average Common and Potential Common Shares 207,252,992 208,888,572 207,927,720 208,858,976 Earnings Allocated to Common and Potential Common Shares $ 308.5 $ 375.4 $ 947.3 $ 1,133.7 Diluted Net Income Per Common Share 1.49 1.80 4.56 5.43

Revenue from Contracts with Cli

Revenue from Contracts with Clients	9 Months Ended
	Sep. 30, 2023
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 67: REVENUE DISAGGREGATION THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Noninterest Income Trust, Investment and Other Servicing Fees Custody and Fund Administration $ 459.0 $ 435.0 $ 1,358.7 $ 1,383.4 Investment Management and Advisory 574.1 565.3 1,673.4 1,765.8 Securities Lending 20.7 21.7 61.3 62.2 Other 58.1 56.7 178.4 179.1 Total Trust, Investment and Other Servicing Fees $ 1,111.9 $ 1,078.7 $ 3,271.8 $ 3,390.5 Other Noninterest Income Foreign Exchange Trading Income $ 51.8 $ 64.7 $ 154.9 $ 223.2 Treasury Management Fees 7.5 9.3 23.8 31.0 Security Commissions and Trading Income 30.9 32.1 101.7 101.1 Other Operating Income 68.2 57.3 170.2 144.0 Investment Security Gains (Losses), net — (0.3) 6.9 (0.3) Total Other Noninterest Income $ 158.4 $ 163.1 $ 457.5 $ 499.0 Total Noninterest Income $ 1,270.3 $ 1,241.8 $ 3,729.3 $ 3,889.5 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 September 30, 2023, revenue from contracts with clients also includes $27.4 million of the $30.9 million total Security Commissions and Trading Income and $11.2 million of the $68.2 million total Other Operating Income. For the nine months ended September 30, 2023, revenue from contracts with clients also includes $86.3 million of the $101.7 million total Security Commissions and Trading Income and $30.5 million of the $170.2 million total Other Operating Income. For the three months ended September 30, 2022, revenue from contracts with clients also includes $27.5 million of the $32.1 million total Security Commissions and Trading Income and $8.9 million of the $57.3 million total Other Operating Income. For the nine months ended September 30, 2022, revenue from contracts with clients also includes $86.4 million of the $101.1 million total Security Commissions and Trading Income and $28.3 million of the $144.0 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 September 30, 2023 and December 31, 2022. TABLE 68: CLIENT RECEIVABLES (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Trust Fees Receivable, net (1) $ 903.0 $ 882.5 Other 57.4 55.4 Total Client Receivables $ 960.4 $ 937.9 (1) Trust Fees Receivable is net of a $14.6 million and $13.5 million fee receivable allowance as of September 30, 2023 and December 31, 2022, respectively.

Net Interest Income

Net Interest Income	9 Months Ended
	Sep. 30, 2023
Banking and Thrift, Interest [Abstract]
Net Interest Income	Net Interest Income The components of Net Interest Income were as follows. TABLE 69: NET INTEREST INCOME THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Interest Income Federal Reserve and Other Central Bank Deposits $ 352.1 $ 135.4 $ 1,128.0 $ 212.2 Interest-Bearing Due from and Deposits with Banks (1) 34.9 14.5 95.2 23.6 Federal Funds Sold — — 0.3 — Securities Purchased under Agreements to Resell 463.9 30.5 874.1 38.4 Securities — Taxable 402.4 237.0 1,106.5 599.7 — Nontaxable (2) 0.3 0.4 1.0 1.1 Loans and Leases 664.2 379.8 1,881.6 827.4 Other Interest-Earning Assets (3) 17.2 1.7 38.7 5.2 Total Interest Income $ 1,935.0 $ 799.3 $ 5,125.4 $ 1,707.6 Interest Expense Deposits $ 716.6 $ 177.3 $ 1,914.7 $ 184.6 Federal Funds Purchased 77.5 9.9 205.2 12.7 Securities Sold Under Agreements to Repurchase 454.0 25.5 843.5 31.8 Other Borrowings 154.8 35.7 446.3 47.2 Senior Notes 44.1 28.6 125.4 57.1 Long-Term Debt 31.8 9.3 91.4 21.5 Total Interest Expense $ 1,478.8 $ 286.3 $ 3,626.5 $ 354.9 Net Interest Income $ 456.2 $ 513.0 $ 1,498.9 $ 1,352.7 (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	9 Months Ended
	Sep. 30, 2023
Other Income and Expenses [Abstract]
Other Operating Income	Other Operating Income The components of Other Operating Income were as follows. TABLE 70: OTHER OPERATING INCOME THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Loan Service Fees $ 21.2 $ 17.8 $ 61.3 $ 52.6 Banking Service Fees 15.0 12.2 40.8 37.8 Bank Owned Life Insurance 17.3 17.3 51.0 44.0 Other Income (1) 14.7 10.0 17.1 9.6 Total Other Operating Income $ 68.2 $ 57.3 $ 170.2 $ 144.0 (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 71: OTHER OPERATING EXPENSE THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, ($ In Millions) 2023 2022 2023 2022 Business Promotion $ 16.2 $ 20.1 $ 53.5 $ 49.0 Staff Related 11.0 7.8 27.7 16.9 FDIC Insurance Premiums 8.3 3.7 21.1 14.1 Charitable Contributions 3.8 5.0 11.3 12.1 Other Expenses 59.2 45.4 182.5 159.5 Total Other Operating Expense $ 98.5 $ 82.0 $ 296.1 $ 251.6

Other Operating Expense

Other Operating Expense	9 Months Ended
	Sep. 30, 2023
Other Income and Expenses [Abstract]
Other Operating Expense	Other Operating Income The components of Other Operating Income were as follows. TABLE 70: OTHER OPERATING INCOME THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Loan Service Fees $ 21.2 $ 17.8 $ 61.3 $ 52.6 Banking Service Fees 15.0 12.2 40.8 37.8 Bank Owned Life Insurance 17.3 17.3 51.0 44.0 Other Income (1) 14.7 10.0 17.1 9.6 Total Other Operating Income $ 68.2 $ 57.3 $ 170.2 $ 144.0 (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 71: OTHER OPERATING EXPENSE THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, ($ In Millions) 2023 2022 2023 2022 Business Promotion $ 16.2 $ 20.1 $ 53.5 $ 49.0 Staff Related 11.0 7.8 27.7 16.9 FDIC Insurance Premiums 8.3 3.7 21.1 14.1 Charitable Contributions 3.8 5.0 11.3 12.1 Other Expenses 59.2 45.4 182.5 159.5 Total Other Operating Expense $ 98.5 $ 82.0 $ 296.1 $ 251.6

Pension

Pension	9 Months Ended
	Sep. 30, 2023
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 and nine months ended September 30, 2023 and 2022. TABLE 72: NET PERIODIC PENSION EXPENSE (BENEFIT) U.S. QUALIFIED PLAN THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Service Cost $ 11.5 $ 11.1 $ 34.5 $ 37.5 Interest Cost 13.5 12.5 40.5 33.1 Expected Return on Plan Assets (25.3) (21.9) (75.9) (62.3) Amortization Net Actuarial Loss 0.4 — 1.2 11.4 Prior Service Cost (Credit) — — — (0.1) Net Periodic Pension Expense $ 0.1 $ 1.7 $ 0.3 $ 19.6 Settlement Expense — 17.0 — 37.3 Total Pension Expense $ 0.1 $ 18.7 $ 0.3 $ 56.9 NON-U.S. PENSION PLANS THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Service Cost $ 0.4 $ 0.4 $ 1.1 $ 1.3 Interest Cost 1.2 0.6 3.6 1.9 Expected Return on Plan Assets (1.6) (0.7) (4.7) (2.2) Amortization Net Actuarial (Gain) Loss (0.1) 0.2 (0.3) 0.6 Net Periodic Pension (Benefit) Expense $ (0.1) $ 0.5 $ (0.3) $ 1.6 Settlement Expense — — — 0.7 Total Pension (Benefit) Expense $ (0.1) $ 0.5 $ (0.3) $ 2.3 U.S. NON-QUALIFIED PLAN THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Service Cost $ 1.2 $ 1.4 $ 3.6 $ 4.2 Interest Cost 1.3 1.0 3.9 3.0 Amortization Net Actuarial Loss 1.3 1.8 3.9 5.4 Net Periodic Pension Expense $ 3.8 $ 4.2 $ 11.4 $ 12.6 The components of net periodic pension expense are recorded in Employee Benefits expense on the consolidated statements of income. There were no contributions to the U.S. Qualified Plan during the nine months ended September 30, 2023 and 2022, and $16.5 million and $20.7 million of contributions to the U.S. Non-Qualified Plan during the nine months ended September 30, 2023 and 2022, respectively.

Share-Based Compensation Plans

Share-Based Compensation Plans	9 Months Ended
	Sep. 30, 2023
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. Total compensation expense for share-based payment arrangements and the associated tax impacts were as follows for the three and nine months ended September 30, 2023 and 2022. TABLE 73: TOTAL COMPENSATION EXPENSE FOR SHARE-BASED PAYMENT ARRANGEMENTS THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Restricted Stock Unit Awards $ 14.7 $ 13.9 $ 80.5 $ 83.4 Performance Stock Units 1.8 0.9 17.8 21.4 Total Share-Based Compensation Expense 16.5 14.8 98.3 104.8 Tax Benefits Recognized $ 4.2 $ 3.7 $ 24.7 $ 26.3

Variable Interest Entities

Variable Interest Entities	9 Months Ended
	Sep. 30, 2023
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 other community development projects. 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 74: SUMMARY OF UNCONSOLIDATED TAX CREDIT STRUCTURES (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Investment Carrying Amount Affordable Housing $ 640.1 $ 635.9 Other Community Development 254.4 268.4 Total Investment Carrying Amount (1) $ 894.5 $ 904.3 Unfunded Commitments Affordable Housing $ 205.5 $ 218.9 Other Community Development — — Total Unfunded Commitments (2) $ 205.5 $ 218.9 (1) As of September 30, 2023 and December 31, 2022, $861.2 million and $867.2 million are VIEs, respectively. (2) As of September 30, 2023 and December 31, 2022, $198.5 million and $210.1 million relate to undrawn commitments on VIEs, respectively. Tax credits and other tax benefits attributable to unconsolidated tax credit structures totaled $28.5 million and $26.1 million for the three months ended September 30, 2023 and 2022, respectively, and $85.1 million and $74.5 million for the nine months ended September 30, 2023, and 2022, respectively. 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 $2.2 million and $2.6 million of money market fund fees for the three months ended September 30, 2023 and 2022, respectively, related to certain competitive factors, and $6.5 million and $61.9 million for the nine months ended September 30, 2023, and 2022, respectively, related to the low interest rate environment at the time and 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. Periodically, Northern Trust makes seed capital investments to certain funds. As of September 30, 2023, Northern Trust had no seed capital investments and no unfunded commitments related to seed capital investments. As of December 31, 2022, Northern Trust had $19.9 million of investments valued using net asset value per share and included in Other Assets and had no unfunded commitments related to seed capital investments.

Commitments and Contingent Liab

Commitments and Contingent Liabilities	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022. TABLE 75: SUMMARY OF OFF-BALANCE SHEET FINANCIAL INSTRUMENTS SEPTEMBER 30, 2023 DECEMBER 31, 2022 ($ In Millions) ONE YEAR AND LESS OVER ONE YEAR TOTAL ONE YEAR AND LESS OVER ONE YEAR TOTAL Undrawn Commitments (1) $ 12,409.2 $ 18,452.1 $ 30,861.3 $ 13,639.2 $ 17,321.4 $ 30,960.6 Standby Letters of Credit and Financial Guarantees (2)(3) 62,939.0 375.8 63,314.8 17,553.0 409.9 17,962.9 Commercial Letters of Credit 24.5 1.3 25.8 25.4 1.3 26.7 Securities Lent with Indemnification 141,392.4 — 141,392.4 130,311.0 — 130,311.0 Unsettled Reverse Repurchase Agreements 19,127.3 — 19,127.3 496.8 — 496.8 Total Off-Balance Sheet Financial Instruments $ 235,892.4 $ 18,829.2 $ 254,721.6 $ 162,025.4 $ 17,732.6 $ 179,758.0 (1) These amounts exclude $222.5 million and $266.6 million of commitments participated to others at September 30, 2023 and December 31, 2022, respectively. (2) These amounts include $33.4 million and $35.1 million of standby letters of credit secured by cash deposits or participated to others as of September 30, 2023 and December 31, 2022, respectively. (3) These amounts include a $61.4 billion and $16.3 billion guarantee to the Fixed Income Clearing Corporation (FICC) under the sponsored member program, without taking into consideration the related collateral, as of September 30, 2023 and December 31, 2022, 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. 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 September 30, 2023 and December 31, 2022 subject to indemnification was $141.4 billion and $130.3 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 September 30, 2023 or December 31, 2022, 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 September 30, 2023 and December 31, 2022, there were $19.1 billion and $496.8 million 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 September 30, 2023 and December 31, 2022, 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 May 2023, the Federal Deposit Insurance Corporation (FDIC) issued a proposed rule that would impose a special assessment to recover the loss to the Deposit Insurance Fund arising from the protection of uninsured depositors of Silicon Valley Bank and Signature Bank associated with their closures, and the systemic risk determination announced by the FDIC on March 12, 2023. While the timing and amount of any expense recognition are unknown until the proposed rule is finalized, if the FDIC final rule is issued as proposed, the estimated impact of the special assessment to Northern Trust, recognized in Other Operating Expense, would be approximately $80 million. 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 September 30, 2023, 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 and the appellate court is expected to render its verdict in March 2024. As trustee, NTFS provided no tax advice and had no involvement in the preparation or filing of the challenged estate tax filings. 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. 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, while other merchants have appealed the approval order granted by the district court. 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 September 13, 2023, Visa announced that it is engaging in discussions with its stockholders regarding potential amendments to its Certificate of Incorporation that would authorize Visa to conduct a potential exchange offer program that would have the effect of releasing the transfer restrictions on portions of Class B common shares. If adopted, the potential amendments would allow Visa Class B shareholders to participate in a potential exchange offer program that would allow them to tender some or all of their Class B 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 would be subject to the same transfer and convertibility restrictions as the currently outstanding Visa Class B common shares. One third of the Visa Class C common shares received would be convertible into Visa Class A common shares at a fixed conversion within the first 45 days following the potential exchange, up to two-thirds would be convertible within the first 90 days, and all such shares would be convertible after 90 days. After the initial potential exchange offer, Visa could, 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 at issue in the unresolved claims for damages in the covered litigation. To become effective, the potential amendments to Visa’s Certificate of Incorporation necessary to facilitate the exchange offer program described must first be approved by holders of a majority of the outstanding Visa Class A, B, and C common shares, each voting as a separate class, following formal proposal by Visa’s board of directors. 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 September 30, 2023 and December 31, 2022.

Derivative Financial Instrument

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022. TABLE 76: NOTIONAL AND FAIR VALUES OF DERIVATIVE FINANCIAL INSTRUMENTS SEPTEMBER 30, 2023 DECEMBER 31, 2022 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 $ 5,566.1 $ 82.8 $ 43.2 $ 4,622.0 $ 58.5 $ 32.7 Foreign Exchange Contracts Cash Flow Hedges 934.4 50.5 — 150.9 7.4 5.7 Net Investment Hedges 3,820.0 126.8 1.2 3,765.0 283.5 12.7 Total Derivatives Designated as Hedging under GAAP $ 10,320.5 $ 260.1 $ 44.4 $ 8,537.9 $ 349.4 $ 51.1 Derivatives Not Designated as Hedging under GAAP Non-Designated Risk Management Derivatives Foreign Exchange Contracts $ 50.5 $ 0.7 $ 0.1 $ 55.9 $ 0.1 $ 0.1 Other Financial Derivatives (3) 768.1 — 28.9 717.7 0.3 34.8 Total Non-Designated Risk Management Derivatives $ 818.6 $ 0.7 $ 29.0 $ 773.6 $ 0.4 $ 34.9 Client-Related and Trading Derivatives Foreign Exchange Contracts $ 311,789.1 $ 2,871.1 $ 2,818.9 $ 288,994.6 $ 3,219.1 $ 3,169.0 Interest Rate Contracts 12,080.7 281.1 424.1 12,378.2 163.5 399.1 Total Client-Related and Trading Derivatives $ 323,869.8 $ 3,152.2 $ 3,243.0 $ 301,372.8 $ 3,382.6 $ 3,568.1 Total Derivatives Not Designated as Hedging under GAAP $ 324,688.4 $ 3,152.9 $ 3,272.0 $ 302,146.4 $ 3,383.0 $ 3,603.0 Total Gross Derivatives $ 335,008.9 $ 3,413.0 $ 3,316.4 $ 310,684.3 $ 3,732.4 $ 3,654.1 Less: Netting (4) 1,553.1 2,409.9 2,810.7 1,865.9 Total Derivative Financial Instruments $ 1,859.9 $ 906.5 $ 921.7 $ 1,788.2 (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) This line includes swaps related to sales of certain Visa Class B common shares and total return swap contracts. (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 enters 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- and nine-month periods ended September 30, 2023 and 2022. 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 enters 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. As of September 30, 2023, foreign exchange contracts to hedge changes in cash flows due to movements in foreign exchange rates of forecasted foreign-currency-denominated transactions were no longer designated as hedging. Northern Trust also enters 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- and nine-month periods ended September 30, 2023 and 2022, as a result of the discontinuance of forecasted transactions that were no longer probable of occurring. It is estimated that net gains of $50.5 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 September 30, 2023, four The following tables provide fair value and cash flow hedge derivative gains and losses recognized in income during the three- and nine-month periods ended September 30, 2023 and 2022. TABLE 77: 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 SEPTEMBER 30, 2023 2022 2023 2022 2023 2022 Total amounts on the consolidated statements of income $ 1,935.0 $ 799.3 $ 1,478.8 $ 286.3 $ 68.2 $ 57.3 Gains (Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives 14.1 32.3 (41.8) (119.9) — — Recognized on hedged items (14.1) (32.3) 41.8 119.9 — — Amounts related to interest settlements on derivatives 11.1 (4.0) (24.9) (6.9) — — Total gains (losses) recognized on fair value hedges $ 11.1 $ (4.0) $ (24.9) $ (6.9) $ — $ — Gains (Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gains (losses) reclassified from AOCI to net income $ 14.6 $ — $ — $ — $ 0.3 $ (0.6) Total gains (losses) reclassified from AOCI to net income on cash flow hedges $ 14.6 $ — $ — $ — $ 0.3 $ (0.6) (In Millions) INTEREST INCOME INTEREST EXPENSE OTHER OPERATING INCOME NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 2023 2022 Total amounts on the consolidated statements of income $ 5,125.4 $ 1,707.6 $ 3,626.5 $ 354.9 $ 170.2 $ 144.0 Gains (Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives 0.6 90.0 (42.5) (373.6) — — Recognized on hedged items (0.6) (90.0) 42.5 373.6 — — Amounts related to interest settlements on derivatives 34.7 (13.3) (65.9) 18.0 — — Total gains (losses) recognized on fair value hedges $ 34.7 $ (13.3) $ (65.9) $ 18.0 $ — $ — Gains (Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gains (losses) reclassified from AOCI to net income $ 15.8 $ 0.6 $ — $ — $ 1.9 $ (4.4) Total gains (losses) reclassified from AOCI to net income on cash flow hedges $ 15.8 $ 0.6 $ — $ — $ 1.9 $ (4.4) The following table provides the impact of fair value hedge accounting on the carrying value of the designated hedged items as of September 30, 2023 and December 31, 2022. TABLE 78: HEDGED ITEMS IN FAIR VALUE HEDGES SEPTEMBER 30, 2023 DECEMBER 31, 2022 (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) $ 2,631.6 $ (55.7) $ 1,820.8 $ (60.2) Senior Notes and Long-Term Subordinated Debt 2,407.6 (336.5) 2,746.2 (294.0) (1) The cumulative hedge accounting basis adjustment includes $2.2 million related to discontinued hedging relationships of AFS debt securities as of September 30, 2023. There are no amounts related to discontinued hedging relationships in the cumulative hedge accounting basis adjustment of senior notes and long-term debt as of September 30, 2023. (2) The cumulative hedge accounting basis adjustment includes $7.3 million related to discontinued hedging relationships of AFS debt securities as of December 31, 2022. There were no amounts related to discontinued hedging relationships in the cumulative hedge accounting basis adjustment of senior notes and long-term debt as of December 31, 2022. (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 $129.9 million and $248.4 million were recognized in AOCI related to foreign exchange contracts for the three months ended September 30, 2023 and 2022, respectively. Net investment hedge gains of $66.8 million and $512.1 million were recognized in AOCI related to foreign exchange contracts for the nine months ended September 30, 2023 and 2022, 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 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 nine months ended September 30, 2023 and 2022 for derivative instruments not designated as hedges under GAAP. TABLE 79: 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 SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 Non-designated risk management derivatives Foreign Exchange Contracts Other Operating Income $ 1.4 $ (0.6) $ 2.9 $ (2.0) Other Financial Derivatives (1) Other Operating Income 2.4 0.7 (18.3) (9.4) Gains (Losses) from non-designated risk management derivatives $ 3.8 $ 0.1 $ (15.4) $ (11.4) Client-related and trading derivatives Foreign Exchange Contracts Foreign Exchange Trading Income $ 51.8 $ 64.7 $ 154.9 $ 223.2 Interest Rate Contracts Security Commissions and Trading Income 1.2 2.9 8.1 7.1 Gains from client-related and trading derivatives $ 53.0 $ 67.6 $ 163.0 $ 230.3 Total gains from derivatives not designated as hedging under GAAP $ 56.8 $ 67.7 $ 147.6 $ 218.9 (1) This line includes swaps related to the sale of certain Visa Class B common shares and total return swap contracts.

Securities Sold Under Agreement

Securities Sold Under Agreements to Repurchase	9 Months Ended
	Sep. 30, 2023
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 agreement and the conditions to net are met. The following table provides information regarding repurchase agreements that are accounted for as secured borrowings as of September 30, 2023 and December 31, 2022. TABLE 80: REPURCHASE AGREEMENTS ACCOUNTED FOR AS SECURED BORROWINGS REMAINING CONTRACTUAL MATURITY OF THE AGREEMENTS SEPTEMBER 30, 2023 DECEMBER 31, 2022 ($ In Millions) OVERNIGHT AND CONTINUOUS U.S. Treasury and Agency Securities $ 545.9 $ 567.2 Total Borrowings 545.9 567.2 Net Amount of Recognized Liabilities for Repurchase Agreements in Note 23 545.9 567.2

Offsetting of Assets and Liabil

Offsetting of Assets and Liabilities	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022. TABLE 81: OFFSETTING OF DERIVATIVE ASSETS AND SECURITIES PURCHASED UNDER AGREEMENTS TO RESELL SEPTEMBER 30, 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 Over the Counter (OTC) $ 2,106.8 $ 1,266.6 $ 840.2 $ 14.3 $ 825.9 Interest Rate Swaps OTC 363.9 286.5 77.4 — 77.4 Total Derivatives Subject to a Master Netting Arrangement 2,470.7 1,553.1 917.6 14.3 903.3 Total Derivatives Not Subject to a Master Netting Arrangement 942.3 — 942.3 — 942.3 Total Derivatives 3,413.0 1,553.1 1,859.9 14.3 1,845.6 Securities Purchased under Agreements to Resell (2) $ 50,143.2 $ 49,758.9 $ 384.3 $ 384.3 $ — DECEMBER 31, 2022 (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 $ 2,928.9 $ 2,666.4 $ 262.5 $ 5.0 $ 257.5 Interest Rate Swaps OTC 217.6 144.3 73.3 — 73.3 Interest Rate Swaps Exchange Cleared 4.4 — 4.4 — 4.4 Other Financial Derivative 0.3 — 0.3 — 0.3 Total Derivatives Subject to a Master Netting Arrangement 3,151.2 2,810.7 340.5 5.0 335.5 Total Derivatives Not Subject to a Master Netting Arrangement 581.2 — 581.2 — 581.2 Total Derivatives 3,732.4 2,810.7 921.7 5.0 916.7 Securities Purchased under Agreements to Resell (2) $ 12,494.2 $ 11,423.9 $ 1,070.3 $ 1,070.3 $ — (1) Derivative assets are reported in Other Assets on the consolidated balance sheets. Other Assets (excluding derivative assets) totaled $10.7 billion and $8.9 billion as of September 30, 2023 and December 31, 2022, 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 September 30, 2023 and December 31, 2022. 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 September 30, 2023 and December 31, 2022. TABLE 82: OFFSETTING OF DERIVATIVE LIABILITIES AND SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE SEPTEMBER 30, 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 $ 2,527.7 $ 2,380.6 $ 147.1 $ — $ 147.1 Interest Rate Swaps OTC 467.3 2.1 465.2 — 465.2 Other Financial Derivatives 28.9 27.2 1.7 — 1.7 Total Derivatives Subject to a Master Netting Arrangement 3,023.9 2,409.9 614.0 — 614.0 Total Derivatives Not Subject to a Master Netting Arrangement 292.5 — 292.5 — 292.5 Total Derivatives 3,316.4 2,409.9 906.5 — 906.5 Securities Sold under Agreements to Repurchase (2) $ 50,304.8 $ 49,758.9 $ 545.9 $ 545.9 $ — DECEMBER 31, 2022 (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 $ 2,082.3 $ 1,826.7 $ 255.6 $ — $ 255.6 Interest Rate Swaps OTC 426.5 5.9 420.6 — 420.6 Interest Rate Swaps Exchange Cleared 5.3 — 5.3 — 5.3 Other Financial Derivatives 34.8 33.3 1.5 — 1.5 Total Derivatives Subject to a Master Netting Arrangement 2,548.9 1,865.9 683.0 — 683.0 Total Derivatives Not Subject to a Master Netting Arrangement 1,105.2 — 1,105.2 — 1,105.2 Total Derivatives 3,654.1 1,865.9 1,788.2 — 1,788.2 Securities Sold under Agreements to Repurchase (2) $ 11,991.1 $ 11,423.9 $ 567.2 $ 567.2 $ — (1) Derivative liabilities are reported in Other Liabilities on the consolidated balance sheets. Other Liabilities (excluding derivative liabilities) totaled $3.7 billion and $3.2 billion as of September 30, 2023 and December 31, 2022, 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 September 30, 2023 and December 31, 2022. 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 and derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. 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. 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 $67.7 million and $473.4 million, respectively, as of September 30, 2023, and $131.8 million and $26.3 million, respectively, as of December 31, 2022, 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 $592.2 million and $190.9 million at September 30, 2023 and December 31, 2022, respectively. Cash collateral amounts deposited with derivative counterparties on those dates included $548.9 million and $55.1 million, respectively, posted against these liabilities, resulting in a net maximum amount of termination payments that could have been required at September 30, 2023 and December 31, 2022, of $43.3 million and $135.8 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						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Pay vs Performance Disclosure
Net Income	$ 327.8	$ 331.8	$ 334.6	$ 394.8	$ 396.2	$ 389.3	$ 994.2	$ 1,180.3

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Sep. 30, 2023
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)	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and 2022, 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, 2023, Northern Trust adopted Accounting Standards Update (ASU) No. 2022-01, “Derivatives and Hedging (Topic 815): Fair Value Hedging—Portfolio Layer Method” (ASU 2022-01). The amendments in ASU 2022-01 expand the current last-of-layer hedging model from a single-layer method to allow multiple hedged layers of a single closed portfolio. To reflect that expansion, the last-of-layer method is renamed the portfolio layer method. In addition, ASU 2022-01 (1) expands the scope of the portfolio layer method to include non-prepayable assets, (2) specifies eligible hedging instruments in a single-layer hedge, (3) provides additional guidance on the accounting for and disclosure of hedge basis adjustments under the portfolio layer method, and (4) specifies how hedge basis adjustments should be considered when determining credit losses for the assets included in the closed portfolio. Upon adoption of ASU 2022-01, there was no impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. On January 1, 2023, Northern Trust adopted ASU No. 2022-02, “Financial Instruments—Credit Losses (Topic 326): Troubled Debt Restructurings and Vintage Disclosures” (ASU 2022-02). The amendments in ASU 2022-02 eliminate the accounting guidance for troubled debt restructurings (TDRs) for creditors that have adopted the current expected credit losses accounting standard while enhancing disclosure requirements for certain loan refinancings and restructurings made to borrowers experiencing financial difficulty. In addition, ASU 2022-02 requires that a public business entity disclose current-period gross charge-offs by year of origination for financing receivables and net investment in leases. Upon adoption of ASU 2022-02, there was no significant impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. Please refer to Note 5—Loans for further information. On January 1, 2023, Northern Trust adopted ASU No. 2022-04, “Liabilities—Supplier Finance Programs (Topic 405-50): Disclosure of Supplier Finance Program Obligations” (ASU 2022-04). The amendments in ASU 2022-04 enhance the transparency about the use of supplier finance programs for investors or other allocators of capital. Specifically, ASU 2022-04 requires that a buyer in a supplier finance program disclose sufficient qualitative and quantitative information about the program to allow a user of financial statements to understand the program’s nature, activity during the period, changes from period to period, and potential magnitude. Upon adoption of ASU 2022-04, there was no impact to Northern Trust’s consolidated balance sheets or consolidated statements of income.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022, 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 35: LEVEL 3 SIGNIFICANT UNOBSERVABLE INPUTS SEPTEMBER 30, 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 $28.9 million Discounted Cash Flow Conversion Rate 1.59x 1.59x Visa Class A Appreciation 10.15% 10.15% Expected Duration 12 - 30 months 16 months (1) Weighted average of expected duration based on scenario probability. DECEMBER 31, 2022 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 $34.8 million Discounted Cash Flow Conversion Rate 1.60x 1.60x Visa Class A Appreciation 8.53% 8.53% Expected Duration 12 - 33 months 20 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 September 30, 2023 and December 31, 2022, 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 38: LEVEL 3 NONRECURRING BASIS SIGNIFICANT UNOBSERVABLE INPUTS SEPTEMBER 30, 2023 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $3.8 million Market Approach Discount factor applied to real estate collateral-dependent loans to reflect realizable value 20.0% 20.0% (1) Includes real estate collateral-dependent loans and other collateral-dependent loans. DECEMBER 31, 2022 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $6.6 million Market Approach Discount factor applied to real estate collateral-dependent loans to reflect realizable value 15.0 % - 20.0% 17.2% (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 September 30, 2023 and December 31, 2022, segregated by fair value hierarchy level. TABLE 36: RECURRING BASIS HIERARCHY LEVELING SEPTEMBER 30, 2023 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 2,879.4 $ — $ — $ — $ 2,879.4 Obligations of States and Political Subdivisions — 282.1 — — 282.1 Government Sponsored Agency — 11,656.8 — — 11,656.8 Non-U.S. Government — 246.9 — — 246.9 Corporate Debt — 380.9 — — 380.9 Covered Bonds — 280.4 — — 280.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,959.8 — — 2,959.8 Other Asset-Backed — 4,771.5 — — 4,771.5 Commercial Mortgage-Backed — 884.3 — — 884.3 Total Available for Sale 2,879.4 21,462.7 — — 24,342.1 Trading Account — 0.1 — — 0.1 Total Available for Sale and Trading Debt Securities 2,879.4 21,462.8 — — 24,342.2 Other Assets Money Market Investment 95.0 — — — 95.0 Derivative Assets Foreign Exchange Contracts — 3,049.1 — (1,266.6) 1,782.5 Interest Rate Contracts — 363.9 — (286.5) 77.4 Other Financial Derivatives — — — — — Total Derivative Assets — 3,413.0 — (1,553.1) 1,859.9 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 2,820.2 — (2,380.6) 439.6 Interest Rate Contracts — 467.3 — (2.1) 465.2 Other Financial Derivatives (1) — — 28.9 (27.2) 1.7 Total Derivative Liabilities $ — $ 3,287.5 $ 28.9 $ (2,409.9) $ 906.5 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 September 30, 2023, derivative assets and liabilities shown above also include reductions of $287.0 million and $1.1 billion, respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1) This line consists of swaps related to the sale of certain Visa Class B common shares. DECEMBER 31, 2022 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 2,747.4 $ — $ — $ — $ 2,747.4 Obligations of States and Political Subdivisions — 787.6 — — 787.6 Government Sponsored Agency — 11,545.2 — — 11,545.2 Non-U.S. Government — 360.0 — — 360.0 Corporate Debt — 1,747.6 — — 1,747.6 Covered Bonds — 388.7 — — 388.7 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,479.4 — — 2,479.4 Other Asset-Backed — 5,256.2 — — 5,256.2 Commercial Mortgage-Backed — 1,387.8 — — 1,387.8 Total Available for Sale 2,747.4 23,952.5 — — 26,699.9 Trading Account 95.0 0.2 — — 95.2 Total Available for Sale and Trading Debt Securities 2,842.4 23,952.7 — — 26,795.1 Other Assets Derivative Assets Foreign Exchange Contracts — 3,510.1 — (2,666.4) 843.7 Interest Rate Contracts — 222.0 — (144.3) 77.7 Other Financial Derivatives (1) — 0.3 — — 0.3 Total Derivative Assets — 3,732.4 — (2,810.7) 921.7 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 3,187.5 — (1,826.7) 1,360.8 Interest Rate Contracts — 431.8 — (5.9) 425.9 Other Financial Derivatives (2) — — 34.8 (33.3) 1.5 Total Derivative Liabilities $ — $ 3,619.3 $ 34.8 $ (1,865.9) $ 1,788.2 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, 2022, derivative assets and liabilities shown above also include reductions of $1.1 billion and $195.3 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1) This line consists of total return swap contracts.
Changes in Level 3 Liabilities	The following table presents the changes in Level 3 liabilities for the three and nine months ended September 30, 2023 and 2022. TABLE 37: CHANGES IN LEVEL 3 LIABILITIES (In Millions) SWAPS RELATED TO SALE OF CERTAIN VISA CLASS B COMMON SHARES THREE MONTHS ENDED SEPTEMBER 30, 2023 2022 Fair Value at July 1 $ 36.4 $ 31.1 Total (Gains) Losses: Included in Earnings (1) (2.4) 1.1 Purchases, Issues, Sales, and Settlements Settlements (5.1) (4.6) Fair Value at September 30 $ 28.9 $ 27.6 (1) (Gains) losses are recorded in Other Operating Income on the consolidated statements of income. NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 Fair Value at January 1 $ 34.8 $ 37.5 Total (Gains) Losses: Included in Earnings (1) 16.1 11.2 Purchases, Issues, Sales, and Settlements Settlements (22.0) (21.1) Fair Value at September 30 $ 28.9 $ 27.6 (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 September 30, 2023 and December 31, 2022. The following tables exclude those items measured at fair value on a recurring basis. TABLE 39: FAIR VALUE OF FINANCIAL INSTRUMENTS SEPTEMBER 30, 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 $ 4,955.7 $ 4,955.7 $ 4,955.7 $ — $ — Federal Reserve and Other Central Bank Deposits 32,316.8 32,316.8 — 32,316.8 — Interest-Bearing Deposits with Banks 2,122.5 2,122.5 — 2,122.5 — Securities Purchased under Agreements to Resell 384.3 384.3 — 384.3 — Debt Securities - Held to Maturity 24,920.4 22,449.7 — 22,449.7 — Loans Held for Investment 43,410.2 43,384.4 — — 43,384.4 Other Assets 1,502.1 1,485.4 89.4 1,396.0 — FINANCIAL LIABILITIES Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 45,300.4 $ 45,300.4 $ 45,300.4 $ — $ — Savings Certificates and Other Time 4,038.6 4,070.4 — 4,070.4 — Non U.S. Offices Interest-Bearing 60,826.9 60,826.9 — 60,826.9 — Federal Funds Purchased 5,539.3 5,539.3 — 5,539.3 — Securities Sold Under Agreements to Repurchase 545.9 545.9 — 545.9 — Other Borrowings 6,870.9 6,888.1 — 6,888.1 — Senior Notes 2,688.9 2,646.6 — 2,646.6 — Long-Term Debt 4,060.7 4,026.1 — 4,026.1 — Unfunded Commitments 205.5 205.5 — 205.5 — Other Liabilities 89.5 89.5 — — 89.5 DECEMBER 31, 2022 ESTIMATED FAIR VALUE (In Millions) BOOK VALUE TOTAL ESTIMATED FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 FINANCIAL ASSETS Cash and Due from Banks $ 4,654.2 $ 4,654.2 $ 4,654.2 $ — $ — Federal Reserve and Other Central Bank Deposits 40,030.4 40,030.4 — 40,030.4 — Interest-Bearing Deposits with Banks 1,941.1 1,941.1 — 1,941.1 — Federal Funds Sold 32.0 32.0 — 32.0 — Securities Purchased under Agreements to Resell 1,070.3 1,070.3 — 1,070.3 — Debt Securities - Held to Maturity 25,036.1 22,879.3 50.0 22,829.3 — Loans Held for Investment 42,749.0 42,636.5 — — 42,636.5 Other Assets 1,476.9 1,460.4 94.7 1,365.7 — FINANCIAL LIABILITIES Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 56,468.9 $ 56,468.9 $ 56,468.9 $ — $ — Savings Certificates and Other Time 1,981.3 1,976.1 — 1,976.1 — Non U.S. Offices Interest-Bearing 65,481.9 65,481.9 — 65,481.9 — Federal Funds Purchased 1,896.9 1,896.9 — 1,896.9 — Securities Sold Under Agreements to Repurchase 567.2 567.2 — 567.2 — Other Borrowings 7,592.3 7,592.8 — 7,592.8 — Senior Notes 2,724.2 2,729.8 — 2,729.8 — Long-Term Debt 2,066.2 2,110.7 — 2,110.7 — Unfunded Commitments 218.9 218.9 — 218.9 — Other Liabilities 73.2 73.2 — — 73.2

Securities (Tables)

Securities (Tables)	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022, and remaining maturities of AFS debt securities as of September 30, 2023. TABLE 40: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF AVAILABLE FOR SALE DEBT SECURITIES SEPTEMBER 30, 2023 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 2,981.2 $ — $ 101.8 $ 2,879.4 Obligations of States and Political Subdivisions 301.5 — 19.4 282.1 Government Sponsored Agency 11,988.1 6.8 338.1 11,656.8 Non-U.S. Government 271.0 — 24.1 246.9 Corporate Debt 397.9 0.1 17.1 380.9 Covered Bonds 292.2 0.1 11.9 280.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,099.2 1.0 140.4 2,959.8 Other Asset-Backed 4,966.1 1.0 195.6 4,771.5 Commercial Mortgage-Backed 948.9 0.1 64.7 884.3 Total $ 25,246.1 $ 9.1 $ 913.1 $ 24,342.1 DECEMBER 31, 2022 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 2,837.7 $ 2.5 $ 92.8 $ 2,747.4 Obligations of States and Political Subdivisions 817.8 — 30.2 787.6 Government Sponsored Agency 11,892.5 4.3 351.6 11,545.2 Non-U.S. Government 387.6 — 27.6 360.0 Corporate Debt 1,774.3 0.2 26.9 1,747.6 Covered Bonds 403.1 0.3 14.7 388.7 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,645.8 0.3 166.7 2,479.4 Other Asset-Backed 5,544.3 — 288.1 5,256.2 Commercial Mortgage-Backed 1,456.9 0.1 69.2 1,387.8 Total $ 27,760.0 $ 7.7 $ 1,067.8 $ 26,699.9
Remaining Maturity of Securities Available for Sale and Held to Maturity	TABLE 41: REMAINING MATURITY OF AVAILABLE FOR SALE DEBT SECURITIES SEPTEMBER 30, 2023 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 $ 297.3 $ 296.4 $ 2,683.9 $ 2,583.0 $ — $ — $ — $ — $ 2,981.2 $ 2,879.4 Obligations of States and Political Subdivisions — — 109.1 102.8 192.4 179.3 — — 301.5 282.1 Government Sponsored Agency 2,294.8 2,250.7 5,259.3 5,113.8 3,481.1 3,389.9 952.9 902.4 11,988.1 11,656.8 Non-U.S. Government — — 271.0 246.9 — — — — 271.0 246.9 Corporate Debt 150.4 148.2 230.9 218.8 16.6 13.9 — — 397.9 380.9 Covered Bonds 141.6 140.1 150.6 140.3 — — — — 292.2 280.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 569.8 563.0 2,465.3 2,347.1 64.1 49.7 — — 3,099.2 2,959.8 Other Asset-Backed 731.5 711.3 3,985.4 3,815.4 248.9 244.5 0.3 0.3 4,966.1 4,771.5 Commercial Mortgage-Backed 38.8 36.7 765.8 729.2 144.3 118.4 — — 948.9 884.3 Total $ 4,224.2 $ 4,146.4 $ 15,921.3 $ 15,297.3 $ 4,147.4 $ 3,995.7 $ 953.2 $ 902.7 $ 25,246.1 $ 24,342.1 Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments. SEPTEMBER 30, 2023 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 $ 58.1 $ 56.9 $ 988.1 $ 941.6 $ 1,187.1 $ 1,095.1 $ 344.4 $ 306.2 $ 2,577.7 $ 2,399.8 Government Sponsored Agency 859.7 727.6 3,105.8 2,649.4 3,408.4 2,901.4 1,786.0 1,475.9 9,159.9 7,754.3 Non-U.S. Government 2,341.3 2,337.5 1,338.1 1,221.1 32.4 26.7 — — 3,711.8 3,585.3 Corporate Debt 96.2 94.6 528.0 494.6 14.9 11.9 — — 639.1 601.1 Covered Bonds 135.5 132.6 1,678.3 1,582.7 303.1 260.0 — — 2,116.9 1,975.3 Certificates of Deposit 405.4 405.5 — — — — — — 405.4 405.5 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 817.0 810.2 4,604.4 4,216.8 22.4 17.8 — — 5,443.8 5,044.8 Other Asset-Backed 43.8 43.7 93.0 93.2 109.8 110.5 — — 246.6 247.4 Commercial Mortgage-Backed — — 37.6 36.9 — — — — 37.6 36.9 Other 34.9 33.6 338.9 292.8 29.8 21.0 178.0 51.9 581.6 399.3 Total $ 4,791.9 $ 4,642.2 $ 12,712.2 $ 11,529.1 $ 5,107.9 $ 4,444.4 $ 2,308.4 $ 1,834.0 $ 24,920.4 $ 22,449.7
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 September 30, 2023 and December 31, 2022. TABLE 42: AVAILABLE FOR SALE DEBT SECURITIES IN UNREALIZED LOSS POSITION WITH NO CREDIT LOSSES REPORTED SEPTEMBER 30, 2023 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ 1,551.0 $ 12.1 $ 1,183.0 $ 89.7 $ 2,734.0 $ 101.8 Obligations of States and Political Subdivisions — — 282.1 19.4 282.1 19.4 Government Sponsored Agency 2,855.0 18.1 7,865.9 320.0 10,720.9 338.1 Non-U.S. Government — — 246.9 24.1 246.9 24.1 Corporate Debt 12.4 0.3 229.9 9.9 242.3 10.2 Covered Bonds — — 214.8 11.9 214.8 11.9 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 302.6 1.9 1,898.2 138.5 2,200.8 140.4 Other Asset-Backed — — 4,561.6 195.6 4,561.6 195.6 Commercial Mortgage-Backed — — 856.7 64.7 856.7 64.7 Total $ 4,721.0 $ 32.4 $ 17,339.1 $ 873.8 $ 22,060.1 $ 906.2 Note: Three corporate debt AFS securities with a fair value of $81.5 million and unrealized losses of $6.9 million have been excluded from the table above as these AFS securities have a $0.7 million allowance for credit losses reported as of September 30, 2023. Refer to the discussion further below and Note 6—Allowance for Credit Losses for further information. DECEMBER 31, 2022 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ 1,123.6 $ 64.1 $ 343.1 $ 28.7 $ 1,466.7 $ 92.8 Obligations of States and Political Subdivisions 160.0 16.8 120.6 13.4 280.6 30.2 Government Sponsored Agency 7,631.4 262.1 2,737.7 89.5 10,369.1 351.6 Non-U.S. Government 235.4 17.3 124.6 10.3 360.0 27.6 Corporate Debt 427.3 14.6 130.3 2.8 557.6 17.4 Covered Bonds 238.0 13.5 42.8 1.2 280.8 14.7 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 1,305.4 74.4 807.1 83.2 2,112.5 157.6 Other Asset-Backed 3,873.4 217.5 1,247.6 70.6 5,121.0 288.1 Commercial Mortgage-Backed 670.9 47.4 215.6 21.8 886.5 69.2 Total $ 15,665.4 $ 727.7 $ 5,769.4 $ 321.5 $ 21,434.8 $ 1,049.2 Note: Three corporate debt AFS securities with a fair value of $93.8 million and unrealized losses of $9.5 million and one sub-sovereign, supranational and non-U.S. agency bonds AFS security with a fair value of $68.3 million and unrealized loss of $9.1 million have been excluded from the table above as these AFS securities have a $1.3 million allowance for credit losses reported as of December 31, 2022. 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 September 30, 2023 and December 31, 2022, and remaining maturities of HTM debt securities as of September 30, 2023.TABLE 43: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF HELD TO MATURITY DEBT SECURITIES SEPTEMBER 30, 2023 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR Obligations of States and Political Subdivisions $ 2,577.7 $ — $ 177.9 $ 2,399.8 Government Sponsored Agency 9,159.9 — 1,405.6 7,754.3 Non-U.S. Government 3,711.8 0.1 126.6 3,585.3 Corporate Debt 639.1 — 38.0 601.1 Covered Bonds 2,116.9 0.4 142.0 1,975.3 Certificates of Deposit 405.4 0.1 — 405.5 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 5,443.8 1.3 400.3 5,044.8 Other Asset-Backed 246.6 1.0 0.2 247.4 Commercial Mortgage-Backed 37.6 — 0.7 36.9 Other 581.6 — 182.3 399.3 Total $ 24,920.4 $ 2.9 $ 2,473.6 $ 22,449.7 DECEMBER 31, 2022 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR U.S. Government $ 50.0 $ — $ — $ 50.0 Obligations of States and Political Subdivisions 2,565.3 — 149.8 2,415.5 Government Sponsored Agency 9,407.7 — 1,076.0 8,331.7 Non-U.S. Government 3,234.0 0.1 133.8 3,100.3 Corporate Debt 713.3 — 45.4 667.9 Covered Bonds 2,530.3 0.3 158.7 2,371.9 Certificates of Deposit 35.9 — — 35.9 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 5,703.3 1.0 436.1 5,268.2 Other Asset-Backed 263.7 — 1.0 262.7 Other 532.6 — 157.4 375.2 Total $ 25,036.1 $ 1.4 $ 2,158.2 $ 22,879.3
Debt Securities, Held-to-maturity, Credit Quality Indicator	The following table provides the amortized cost of HTM debt securities by credit rating. TABLE 45: AMORTIZED COST OF HELD TO MATURITY DEBT SECURITIES BY CREDIT RATING SEPTEMBER 30, 2023 (In Millions) AAA AA A BBB NOT RATED TOTAL Obligations of States and Political Subdivisions $ 918.0 $ 1,659.7 $ — $ — $ — $ 2,577.7 Government Sponsored Agency 9,159.9 — — — — 9,159.9 Non-U.S. Government 894.1 879.0 1,619.7 319.0 — 3,711.8 Corporate Debt 2.2 299.2 337.7 — — 639.1 Covered Bonds 2,116.9 — — — — 2,116.9 Certificates of Deposit 367.4 — — — 38.0 405.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 4,162.6 1,251.3 28.8 1.1 — 5,443.8 Other Asset-Backed 246.6 — — — — 246.6 Commercial Mortgage-Backed 37.6 — — — — 37.6 Other 56.0 — — — 525.6 581.6 Total $ 17,961.3 $ 4,089.2 $ 1,986.2 $ 320.1 $ 563.6 $ 24,920.4 Percent of Total 72 % 17 % 8 % 1 % 2 % 100 % DECEMBER 31, 2022 (In Millions) AAA AA A BBB NOT RATED TOTAL U.S. Government $ 50.0 $ — $ — $ — $ — $ 50.0 Obligations of States and Political Subdivisions 926.8 1,638.5 — — — 2,565.3 Government Sponsored Agency 9,407.7 — — — — 9,407.7 Non-U.S. Government 762.2 926.5 1,223.0 322.3 — 3,234.0 Corporate Debt 2.1 305.7 405.5 — — 713.3 Covered Bonds 2,530.3 — — — — 2,530.3 Certificates of Deposit — — — — 35.9 35.9 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 4,171.3 1,502.0 28.9 1.1 — 5,703.3 Other Asset-Backed 263.7 — — — — 263.7 Other 65.8 — — — 466.8 532.6 Total $ 18,179.9 $ 4,372.7 $ 1,657.4 $ 323.4 $ 502.7 $ 25,036.1 Percent of Total 73 % 17 % 7 % 1 % 2 % 100 %

Loans (Tables)

Loans (Tables)	9 Months Ended
	Sep. 30, 2023
Receivables [Abstract]
Loans	Amounts outstanding for Loans, by segment and class, are shown in the following table. TABLE 46: LOANS (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Commercial Commercial and Institutional (1) $ 12,061.3 $ 12,415.0 Commercial Real Estate 5,063.1 4,773.0 Non-U.S. (1) 2,857.8 3,131.1 Other 2,005.1 1,316.5 Total Commercial 21,987.3 21,635.6 Personal Private Client 14,068.6 14,119.0 Residential Real Estate 6,285.8 6,413.5 Non-U.S. 432.6 510.0 Other 802.7 215.2 Total Personal 21,589.7 21,257.7 Total Loans $ 43,577.0 $ 42,893.3
Borrower Ratings	Loan segment and class balances as of September 30, 2023 and December 31, 2022 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 47: CREDIT QUALITY INDICATOR AT AMORTIZED COST BASIS BY ORIGINATION YEAR September 30, 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 $ 355.1 $ 539.8 $ 874.3 $ 95.9 $ 148.3 $ 417.6 $ 5,148.5 $ 16.0 $ 7,595.5 4 to 5 Category 689.9 818.7 669.7 147.6 125.0 180.4 1,549.0 75.3 4,255.6 6 to 9 Category 13.9 71.1 69.3 12.2 0.1 1.7 41.5 0.4 210.2 Total Commercial and Institutional 1,058.9 1,429.6 1,613.3 255.7 273.4 599.7 6,739.0 91.7 12,061.3 Commercial Real Estate Risk Rating: 1 to 3 Category 334.2 331.8 183.5 19.1 40.8 45.9 47.7 0.5 1,003.5 4 to 5 Category 1,360.9 1,260.2 541.7 228.7 254.9 136.7 202.7 7.4 3,993.2 6 to 9 Category 16.2 3.3 21.6 — 8.2 14.6 2.5 — 66.4 Total Commercial Real Estate 1,711.3 1,595.3 746.8 247.8 303.9 197.2 252.9 7.9 5,063.1 Commercial Real Estate Gross Charge-offs — (4.5) — — — — — — (4.5) Non-U.S. Risk Rating: 1 to 3 Category 842.6 — 43.9 65.4 35.8 3.2 823.5 — 1,814.4 4 to 5 Category 689.6 0.8 — — 23.1 180.2 88.7 — 982.4 6 to 9 Category 46.5 14.5 — — — — — — 61.0 Total Non-U.S. 1,578.7 15.3 43.9 65.4 58.9 183.4 912.2 — 2,857.8 Other Risk Rating: 1 to 3 Category 1,190.9 — — — — — — — 1,190.9 4 to 5 Category 814.2 — — — — — — — 814.2 Total Other 2,005.1 — — — — — — — 2,005.1 Total Commercial 6,354.0 3,040.2 2,404.0 568.9 636.2 980.3 7,904.1 99.6 21,987.3 Commercial Gross Charge-offs — (4.5) — — — — — — (4.5) Personal Private Client Risk Rating: 1 to 3 Category 326.5 218.2 44.4 70.0 15.1 25.0 5,723.2 172.8 6,595.2 4 to 5 Category 305.3 467.8 686.6 99.9 155.4 165.7 5,115.6 429.5 7,425.8 6 to 9 Category 18.3 4.4 — — — 17.8 7.1 — 47.6 Total Private Client 650.1 690.4 731.0 169.9 170.5 208.5 10,845.9 602.3 14,068.6 Residential Real Estate Risk Rating: 1 to 3 Category 198.7 536.2 565.4 405.1 154.2 729.2 229.2 — 2,818.0 4 to 5 Category 115.1 644.7 682.6 672.1 273.7 863.7 142.9 — 3,394.8 6 to 9 Category — 17.5 5.5 2.2 11.0 33.8 3.0 — 73.0 Total Residential Real Estate 313.8 1,198.4 1,253.5 1,079.4 438.9 1,626.7 375.1 — 6,285.8 Residential Real Estate Gross Write-offs (0.8) — — — — (0.3) — — (1.1) Non-U.S. Risk Rating: 1 to 3 Category 16.1 3.7 0.6 — — 5.5 54.0 — 79.9 4 to 5 Category 9.0 20.7 39.4 — 18.8 8.3 249.0 7.5 352.7 Total Non-U.S. 25.1 24.4 40.0 — 18.8 13.8 303.0 7.5 432.6 Other Risk Rating: 1 to 3 Category 90.5 — — — — — — — 90.5 4 to 5 Category 712.2 — — — — — — — 712.2 Total Other 802.7 — — — — — — — 802.7 Total Personal 1,791.7 1,913.2 2,024.5 1,249.3 628.2 1,849.0 11,524.0 609.8 21,589.7 Personal Gross Charge-offs (0.8) — — — — (0.3) — — (1.1) Total Loans $ 8,145.7 $ 4,953.4 $ 4,428.5 $ 1,818.2 $ 1,264.4 $ 2,829.3 $ 19,428.1 $ 709.4 $ 43,577.0 Total Loans Gross Charge-offs $ (0.8) $ (4.5) $ — $ — $ — $ (0.3) $ — $ — $ (5.6) December 31, 2022 TERM LOANS REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2022 2021 2020 2019 2018 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 753.3 $ 1,087.5 $ 209.8 $ 159.3 $ 45.9 $ 511.3 $ 6,032.8 $ 17.7 $ 8,817.6 4 to 5 Category 744.1 740.6 300.8 191.1 151.4 174.7 1,102.3 32.9 3,437.9 6 to 9 Category 50.8 30.5 — 13.7 — — 64.5 — 159.5 Total Commercial and Institutional 1,548.2 1,858.6 510.6 364.1 197.3 686.0 7,199.6 50.6 12,415.0 Commercial Real Estate Risk Rating: 1 to 3 Category 318.7 227.4 123.6 123.5 39.8 39.1 113.4 3.0 988.5 4 to 5 Category 968.5 1,040.0 637.8 447.3 153.0 256.9 181.5 17.5 3,702.5 6 to 9 Category 7.7 22.7 — 49.1 — — 2.5 — 82.0 Total Commercial Real Estate 1,294.9 1,290.1 761.4 619.9 192.8 296.0 297.4 20.5 4,773.0 Non-U.S. Risk Rating: 1 to 3 Category 991.9 46.2 109.6 14.8 — 6.5 1,158.3 — 2,327.3 4 to 5 Category 459.0 — — — — 214.9 89.5 1.8 765.2 6 to 9 Category 0.1 — — 23.1 — — 15.4 — 38.6 Total Non-U.S. 1,451.0 46.2 109.6 37.9 — 221.4 1,263.2 1.8 3,131.1 Other Risk Rating: 1 to 3 Category 993.9 — — — — — — — 993.9 4 to 5 Category 322.6 — — — — — — — 322.6 Total Other 1,316.5 — — — — — — — 1,316.5 Total Commercial 5,610.6 3,194.9 1,381.6 1,021.9 390.1 1,203.4 8,760.2 72.9 21,635.6 Personal Private Client Risk Rating: 1 to 3 Category 395.5 159.9 50.5 313.6 13.4 18.5 5,352.5 28.2 6,332.1 4 to 5 Category 430.3 755.1 192.4 191.3 38.7 160.0 5,728.6 267.2 7,763.6 6 to 9 Category 0.9 — 0.1 — 18.6 — 3.7 — 23.3 Total Private Client 826.7 915.0 243.0 504.9 70.7 178.5 11,084.8 295.4 14,119.0 Residential Real Estate Risk Rating: 1 to 3 Category 871.6 666.7 567.7 168.1 102.9 750.8 128.4 7.9 3,264.1 4 to 5 Category 354.3 656.7 597.6 290.0 170.9 838.2 180.4 1.0 3,089.1 6 to 9 Category — 6.8 1.5 1.1 3.7 35.9 11.3 — 60.3 Total Residential Real Estate 1,225.9 1,330.2 1,166.8 459.2 277.5 1,624.9 320.1 8.9 6,413.5 Non-U.S. Risk Rating: 1 to 3 Category 3.0 3.7 — — 4.6 2.3 124.6 — 138.2 4 to 5 Category 24.2 40.3 — 21.3 3.2 2.9 272.0 7.8 371.7 6 to 9 Category — — — — — 0.1 — — 0.1 Total Non-U.S. 27.2 44.0 — 21.3 7.8 5.3 396.6 7.8 510.0 Other Risk Rating: 1 to 3 Category 190.8 — — — — — — — 190.8 4 to 5 Category 24.4 — — — — — — — 24.4 Total Other 215.2 — — — — — — — 215.2 Total Personal 2,295.0 2,289.2 1,409.8 985.4 356.0 1,808.7 11,801.5 312.1 21,257.7 Total Loans $ 7,905.6 $ 5,484.1 $ 2,791.4 $ 2,007.3 $ 746.1 $ 3,012.1 $ 20,561.7 $ 385.0 $ 42,893.3
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 September 30, 2023 and December 31, 2022. TABLE 48: DELINQUENCY STATUS ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS September 30, 2023 Commercial Commercial and Institutional $ 12,032.4 $ 7.9 $ 1.6 $ 3.1 $ 12,045.0 $ 16.3 $ 12,061.3 $ 6.9 Commercial Real Estate 5,059.9 — — — 5,059.9 3.2 5,063.1 3.2 Non-U.S. 2,854.8 3.0 — — 2,857.8 — 2,857.8 — Other 2,005.1 — — — 2,005.1 — 2,005.1 — Total Commercial 21,952.2 10.9 1.6 3.1 21,967.8 19.5 21,987.3 10.1 Personal Private Client 13,911.3 91.0 13.4 33.1 14,048.8 19.8 14,068.6 17.8 Residential Real Estate 6,254.9 — 1.4 — 6,256.3 29.5 6,285.8 28.1 Non-U.S. 432.6 — — — 432.6 — 432.6 — Other 802.7 — — — 802.7 — 802.7 — Total Personal 21,401.5 91.0 14.8 33.1 21,540.4 49.3 21,589.7 45.9 Total Loans $ 43,353.7 $ 101.9 $ 16.4 $ 36.2 $ 43,508.2 $ 68.8 $ 43,577.0 $ 56.0 Other Real Estate Owned $ 0.3 Total Nonaccrual Assets $ 69.1 ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS December 31, 2022 Commercial Commercial and Institutional $ 12,353.7 $ 40.2 $ 3.0 $ 0.7 $ 12,397.6 $ 17.4 $ 12,415.0 $ 4.4 Commercial Real Estate 4,761.5 1.3 — — 4,762.8 10.2 4,773.0 6.2 Non-U.S. 3,131.1 — — — 3,131.1 — 3,131.1 — Other 1,316.5 — — — 1,316.5 — 1,316.5 — Total Commercial 21,562.8 41.5 3.0 0.7 21,608.0 27.6 21,635.6 10.6 Personal Private Client 13,843.5 192.3 29.9 53.3 14,119.0 — 14,119.0 — Residential Real Estate 6,373.2 9.6 12.3 0.1 6,395.2 18.3 6,413.5 18.3 Non-U.S 509.9 — — 0.1 510.0 — 510.0 — Other 215.2 — — — 215.2 — 215.2 — Total Personal 20,941.8 201.9 42.2 53.5 21,239.4 18.3 21,257.7 18.3 Total Loans $ 42,504.6 $ 243.4 $ 45.2 $ 54.2 $ 42,847.4 $ 45.9 $ 42,893.3 $ 28.9 Other Real Estate Owned $ — Total Nonaccrual Assets $ 45.9
Modified Troubled Debt Restructurings	The following table provides, by segment and class, the number of TDR modifications of loans entered into during the three and nine months ended September 30, 2022, and the recorded investments and unpaid principal balances as of September 30, 2022. TABLE 51: TROUBLED DEBT RESTRUCTURINGS THREE MONTHS ENDED SEPTEMBER 30, 2022 NINE MONTHS ENDED SEPTEMBER 30, 2022 ($ In Millions) LOAN MODIFICATION DETAIL NUMBER OF RECORDED UNPAID NUMBER OF RECORDED UNPAID Commercial Commercial and Institutional Interest rate concession, extension of term and other modification 1 $ 0.1 $ 0.1 2 $ 0.6 $ 0.6 Commercial Real Estate Interest rate concession and other modification 1 31.6 32.5 1 31.6 32.5 Total Commercial 2 31.7 32.6 3 32.2 33.1 Personal Residential Real Estate Interest rate concession, deferrals of principal, extension of term and other modification 1 0.1 0.1 3 0.2 0.2 Total Personal 1 0.1 0.1 3 0.2 0.2 Total Loans and Leases 3 $ 31.8 $ 32.7 6 $ 32.4 $ 33.3 Note: Period-end balances reflect all pay downs and charge-offs during the year.
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 September 30, 2023, disaggregated by relevant class of financing receivable and type of modification provided. TABLE 49: LOAN MODIFICATIONS MADE TO BORROWERS EXPERIENCING FINANCIAL DIFFICULTY THREE MONTHS ENDED SEPTEMBER 30, 2023 NINE MONTHS ENDED SEPTEMBER 30, 2023 (in $ million) LOAN MODIFICATION DETAIL AMORTIZED COST BASIS % OF TOTAL SEGMENT AMORTIZED COST BASIS % OF TOTAL SEGMENT Commercial Commercial and Institutional Extension of term $ 16.7 0.14 % $ 16.7 0.14 % Commercial Real Estate Combination of principal and/or interest deferral and extension of term — — — (1) — Total Commercial 16.7 0.08 16.7 0.08 Personal Residential Real Estate Principal and/or interest deferral 0.1 — 3.2 0.05 Residential Real Estate Combination of principal and/or interest deferral and extension of term 4.7 0.08 4.7 0.08 Private Client Extension of term — — — (1) — Total Personal 4.8 0.02 7.9 0.04 Total Loans $ 21.5 0.05 % $ 24.6 0.06 % (1) Included are financially distressed modifications of $32.5 million (combinations of principal and/or interest deferral and term extensions) for the commercial real estate portfolio and $0.2 million (term extensions) for the private client portfolio for which the respective loans had no amortized cost basis as of the end of the respective period. The $32.5 million loan was fully repaid during the second quarter of 2023. The following table describes the financial effect of the modifications made to borrowers experiencing financial difficulty. TABLE 50: FINANCIAL EFFECT OF MODIFICATIONS MADE TO BORROWERS EXPERIENCING FINANCIAL DIFFICULTY THREE MONTHS ENDED SEPTEMBER 30, 2023 NINE MONTHS ENDED SEPTEMBER 30, 2023 FINANCIAL EFFECT FINANCIAL EFFECT PRINCIPAL AND INTEREST DEFERRAL Commercial Commercial Real Estate — Northern Trust provided a weighted average of 6 months payment deferrals to borrowers for total deferred principal and interest of $32.5 million. Personal Residential Real Estate Northern Trust provided a weighted average of 9 months payment deferrals to borrowers for immaterial principal and interest deferral amounts. Northern Trust provided a weighted average of 9 months payment deferrals to borrowers for immaterial principal and interest deferral amounts. TERM EXTENSION Commercial Commercial and Institutional Northern Trust provided weighted average term extensions of 12 months. Northern Trust provided weighted average term extensions of 12 months. Commercial Real Estate — Northern Trust provided weighted average term extensions of 6 months. Personal Residential Real Estate Northern Trust provided weighted average term extensions of 9 months. Northern Trust provided weighted average term extensions of 9 months. Private Client — Northern Trust provided weighted average term extensions of 60 months.

Allowance for Credit Losses (Ta

Allowance for Credit Losses (Tables)	9 Months Ended
	Sep. 30, 2023
Receivables [Abstract]
Allowance for Credit Loss	The following table provides information regarding changes in the total allowance for credit losses during the three and nine months ended September 30, 2023 and 2022. TABLE 52: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES THREE MONTHS ENDED SEPTEMBER 30, 2023 (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 $ 152.5 $ 26.0 $ 16.7 $ 1.0 $ 196.2 Charge-Offs (0.8) — — — (0.8) Recoveries 1.1 — — — 1.1 Net Recoveries (Charge-Offs) 0.3 — — — 0.3 Provision for (Release of) Credit Losses (1) 14.0 2.3 (1.8) 0.1 14.6 Balance at End of Period $ 166.8 $ 28.3 $ 14.9 $ 1.1 $ 211.1 (1) The table excludes a release of credit reserves of $0.6 million for the three months ended September 30, 2023 for AFS debt securities. NINE MONTHS ENDED SEPTEMBER 30, 2023 (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 $ 144.3 $ 38.5 $ 16.0 $ 0.8 $ 199.6 Charge-Offs (5.6) — — — (5.6) Recoveries 3.0 — — — 3.0 Net Recoveries (Charge-Offs) (2.6) — — — (2.6) Provision for (Release of) Credit Losses (1) 25.1 (10.2) (1.1) 0.3 14.1 Balance at End of Period $ 166.8 $ 28.3 $ 14.9 $ 1.1 $ 211.1 (1) The table excludes a release of credit reserves of $0.6 million for the nine months ended September 30, 2023 for AFS debt securities. See further detail in Note 4—Securities. THREE MONTHS ENDED SEPTEMBER 30, 2022 (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 $ 138.2 $ 43.5 $ 15.4 $ 1.1 $ 198.2 Charge-Offs (5.4) — — — (5.4) Recoveries 0.9 — — — 0.9 Net Recoveries (Charge-Offs) (4.5) — — — (4.5) Provision for (Release of) Credit Losses (1) 5.0 (2.8) (0.4) (0.4) 1.4 Balance at End of Period $ 138.7 $ 40.7 $ 15.0 $ 0.7 $ 195.1 (1) The table excludes a release of credit reserves of $0.9 million for the three months ended September 30, 2022 for AFS debt securities. See further detail in Note 4—Securities. NINE MONTHS ENDED SEPTEMBER 30, 2022 (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 $ 138.4 $ 34.1 $ 11.2 $ 1.0 $ 184.7 Charge-Offs (5.5) — — — (5.5) Recoveries 9.7 — — — 9.7 Net Recoveries (Charge-Offs) 4.2 — — — 4.2 Provision for (Release of) Credit Losses (1) (3.9) 6.6 3.8 (0.3) 6.2 Balance at End of Period $ 138.7 $ 40.7 $ 15.0 $ 0.7 $ 195.1 (1) The table excludes a provision for credit losses of $0.8 million for the nine months ended September 30, 2022 for AFS debt securities. See further detail in Note 4—Securities. TABLE 53: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO LOANS THREE MONTHS ENDED SEPTEMBER 30, 2023 LOANS UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 124.0 $ 28.5 $ 152.5 $ 23.3 $ 2.7 $ 26.0 Charge-Offs (0.5) (0.3) (0.8) — — — Recoveries — 1.1 1.1 — — — Net Recoveries (Charge-Offs) (0.5) 0.8 0.3 — — — Provision for (Release of) Credit Losses 13.9 0.1 14.0 2.2 0.1 2.3 Balance at End of Period $ 137.4 $ 29.4 $ 166.8 $ 25.5 $ 2.8 $ 28.3 NINE MONTHS ENDED SEPTEMBER 30, 2023 LOANS 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 (4.5) (1.1) (5.6) — — — Recoveries 0.1 2.9 3.0 — — — Net Recoveries (Charge-Offs) (4.4) 1.8 (2.6) — — — Provision for (Release of) Credit Losses 25.6 (0.5) 25.1 (10.8) 0.6 (10.2) Balance at End of Period $ 137.4 $ 29.4 $ 166.8 $ 25.5 $ 2.8 $ 28.3 THREE MONTHS ENDED SEPTEMBER 30, 2022 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 102.5 $ 35.7 $ 138.2 $ 40.3 $ 3.2 $ 43.5 Charge-Offs (4.9) (0.5) (5.4) — — — Recoveries 0.3 0.6 0.9 — — — Net Recoveries (Charge-Offs) (4.6) 0.1 (4.5) — — — Provision for (Release of) Credit Losses 2.7 2.3 5.0 (2.8) — (2.8) Balance at End of Period $ 100.6 $ 38.1 $ 138.7 $ 37.5 $ 3.2 $ 40.7 NINE MONTHS ENDED SEPTEMBER 30, 2022 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 105.6 $ 32.8 $ 138.4 $ 31.4 $ 2.7 $ 34.1 Charge-Offs (4.9) (0.6) (5.5) — — — Recoveries 2.7 7.0 9.7 — — — Net Recoveries (Charge-Offs) (2.2) 6.4 4.2 — — — Provision for (Release of) Credit Losses (2.8) (1.1) (3.9) 6.1 0.5 6.6 Balance at End of Period $ 100.6 $ 38.1 $ 138.7 $ 37.5 $ 3.2 $ 40.7 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 September 30, 2023 and December 31, 2022. TABLE 54: RECORDED INVESTMENTS IN LOANS SEPTEMBER 30, 2023 DECEMBER 31, 2022 (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Loans Evaluated on an Individual Basis $ 27.4 $ 67.3 $ 94.7 $ 63.0 $ 46.1 $ 109.1 Evaluated on a Collective Basis 21,959.9 21,522.4 43,482.3 21,572.6 21,211.6 42,784.2 Total Loans 21,987.3 21,589.7 43,577.0 21,635.6 21,257.7 42,893.3 Allowance for Credit Losses on Loans Evaluated on an Individual Basis 8.3 2.0 10.3 10.4 — 10.4 Evaluated on a Collective Basis 129.1 27.4 156.5 105.8 28.1 133.9 Allowance Assigned to Loans 137.4 29.4 166.8 116.2 28.1 144.3 Allowance for Undrawn Loan Commitments and Standby Letters of Credit Evaluated on an Individual Basis — — — — — — Evaluated on a Collective Basis 25.5 2.8 28.3 36.3 2.2 38.5 Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit 25.5 2.8 28.3 36.3 2.2 38.5 Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit $ 162.9 $ 32.2 $ 195.1 $ 152.5 $ 30.3 $ 182.8
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 and nine months ended September 30, 2023 and 2022. TABLE 55: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO HELD TO MATURITY DEBT SECURITIES THREE MONTHS ENDED SEPTEMBER 30, 2023 (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 $ 1.4 $ 5.4 $ 3.4 $ 1.3 $ 0.1 $ 5.1 $ 16.7 Provision for (Release of) Credit Losses (0.1) (0.8) (0.5) (0.1) — (0.3) (1.8) Balance at End of Period $ 1.3 $ 4.6 $ 2.9 $ 1.2 $ 0.1 $ 4.8 $ 14.9 (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. NINE MONTHS ENDED SEPTEMBER 30, 2023 (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 $ 1.9 $ 3.6 $ 4.0 $ 1.5 $ 0.1 $ 4.9 $ 16.0 Provision for (Release of) Credit Losses (0.6) 1.0 (1.1) (0.3) — (0.1) (1.1) Balance at End of Period $ 1.3 $ 4.6 $ 2.9 $ 1.2 $ 0.1 $ 4.8 $ 14.9 (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 SEPTEMBER 30, 2022 (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 $ 1.8 $ 3.8 $ 4.8 $ — $ 0.1 $ 4.9 $ 15.4 Provision for (Release of) Credit Losses (0.3) (0.7) (1.0) — — 1.6 (0.4) Balance at End of Period $ 1.5 $ 3.1 $ 3.8 $ — $ 0.1 $ 6.5 $ 15.0 NINE MONTHS ENDED SEPTEMBER 30, 2022 (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 $ 1.4 $ 1.9 $ 3.0 $ — $ 0.1 $ 4.8 $ 11.2 Provision for (Release of) Credit Losses 0.1 1.2 0.8 — — 1.7 3.8 Balance at End of Period $ 1.5 $ 3.1 $ 3.8 $ — $ 0.1 $ 6.5 $ 15.0
Schedule of Accrued Liabilities	The following table provides the amount of accrued interest excluded from the amortized cost basis of the following portfolios. TABLE 56: ACCRUED INTEREST (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Loans $ 249.4 $ 203.1 Debt Securities Held to Maturity 82.7 63.2 Available for Sale 138.0 147.1 Other Financial Assets 58.4 43.8 Total $ 528.5 $ 457.2

Pledged Assets, Collateral an_2

Pledged Assets, Collateral and Restricted Assets (Tables)	9 Months Ended
	Sep. 30, 2023
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 57: TYPE OF PLEDGED ASSETS (In Billions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Debt Securities (1) $ 27.8 $ 31.4 Loans (2) 11.2 11.8 Total Pledged Assets $ 39.0 $ 43.2 (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. The following table presents the AFS debt securities pledged as collateral that are included in pledged assets. TABLE 58: FAIR VALUE OF AVAILABLE FOR SALE DEBT SECURITIES INCLUDED IN PLEDGED ASSETS SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE DERIVATIVE CONTRACTS (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 SEPTEMBER 30, 2023 DECEMBER 31, 2022 Debt Securities Available for Sale $ 540.7 $ 464.7 $ 15.6 $ 34.7
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 59: ACCEPTED COLLATERAL (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Collateral that may be repledged or sold Reverse repurchase agreements (1)(2) $ 49,972.7 $ 12,119.4 Derivative contracts 14.3 5.0 Collateral that may not be repledged or sold Reverse repurchase agreements — 450.0 Total Collateral Accepted $ 49,987.0 $ 12,574.4 (1) The fair value of securities collateral that was repledged or sold totaled $49.6 billion and $11.5 billion at September 30, 2023 and December 31, 2022, 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)	9 Months Ended
	Sep. 30, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill by Reporting Segment	Changes by reporting segment in the carrying amount of Goodwill for the nine months ended September 30, 2023, including the effect of foreign exchange rates on non-U.S. dollar denominated balances, were as follows. TABLE 60: GOODWILL (In Millions) ASSET WEALTH MANAGEMENT TOTAL Balance at December 31, 2022 $ 611.0 $ 80.3 $ 691.3 Foreign Exchange Rates 1.5 — 1.5 Balance at September 30, 2023 $ 612.5 $ 80.3 $ 692.8
Other Intangible Assets	The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of September 30, 2023 and December 31, 2022 were as follows. TABLE 61: OTHER INTANGIBLE ASSETS (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Gross Carrying Amount $ 128.7 $ 197.9 Less: Accumulated Amortization 58.4 120.3 Net Book Value $ 70.3 $ 77.6 TABLE 62: CAPITALIZED SOFTWARE (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Gross Carrying Amount $ 3,896.1 $ 3,479.3 Less: Accumulated Amortization 1,881.6 1,517.4 Net Book Value $ 2,014.5 $ 1,961.9

Reporting Segments (Tables)

Reporting Segments (Tables)	9 Months Ended
	Sep. 30, 2023
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- and nine-month periods ended September 30, 2023 and 2022. TABLE 63: RESULTS OF REPORTING SEGMENTS ($ In Millions) ASSET SERVICING WEALTH MANAGEMENT OTHER RECONCILING ITEMS TOTAL CONSOLIDATED THREE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 2023 2022 2023 2022 2023 2022 Noninterest Income Trust, Investment and Other Servicing Fees $ 626.0 $ 603.2 $ 485.9 $ 475.5 $ — $ — $ — $ — $ 1,111.9 $ 1,078.7 Foreign Exchange Trading Income (Loss) 54.3 63.7 (2.5) 1.0 — — — — 51.8 64.7 Other Noninterest Income (Loss) 66.1 62.5 38.1 37.0 2.4 (1.1) — — 106.6 98.4 Total Noninterest Income (Loss) 746.4 729.4 521.5 513.5 2.4 (1.1) — — 1,270.3 1,241.8 Net Interest Income 281.2 303.3 188.2 222.0 — — (13.2) (12.3) 456.2 513.0 Revenue 1,027.6 1,032.7 709.7 735.5 2.4 (1.1) (13.2) (12.3) 1,726.5 1,754.8 Provision for (Release of) Credit Losses 3.1 (5.1) 10.9 5.6 — — — — 14.0 0.5 Noninterest Expense 809.3 760.4 456.9 449.0 12.0 20.4 — — 1,278.2 1,229.8 Income before Income Taxes 215.2 277.4 241.9 280.9 (9.6) (21.5) (13.2) (12.3) 434.3 524.5 Provision for Income Taxes 54.3 67.7 67.7 79.6 (2.3) (5.3) (13.2) (12.3) 106.5 129.7 Net Income $ 160.9 $ 209.7 $ 174.2 $ 201.3 $ (7.3) $ (16.2) $ — $ — $ 327.8 $ 394.8 Percentage of Consolidated Net Income 49 % 53 % 53 % 51 % (2) % (4) % N/A N/A 100 % 100 % Average Assets $ 108,656.7 $ 109,677.2 $ 31,544.9 $ 36,725.0 $ — $ — N/A N/A $ 140,201.6 $ 146,402.2 ($ In Millions) ASSET SERVICING WEALTH MANAGEMENT OTHER RECONCILING ITEMS TOTAL CONSOLIDATED NINE MONTHS ENDED 2023 2022 2023 2022 2023 2022 2023 2022 2023 2022 Noninterest Income Trust, Investment and Other Servicing Fees $ 1,850.2 $ 1,908.4 $ 1,421.6 $ 1,482.1 $ — $ — $ — $ — $ 3,271.8 $ 3,390.5 Foreign Exchange Trading Income (Loss) 161.2 215.9 (6.3) 7.3 — — — — 154.9 223.2 Other Noninterest Income (Loss) 199.0 185.4 112.8 101.6 (9.2) (11.2) — — 302.6 275.8 Total Noninterest Income (Loss) 2,210.4 2,309.7 1,528.1 1,591.0 (9.2) (11.2) — — 3,729.3 3,889.5 Net Interest Income 902.6 748.5 635.8 634.3 — — (39.5) (30.1) 1,498.9 1,352.7 Revenue 3,113.0 3,058.2 2,163.9 2,225.3 (9.2) (11.2) (39.5) (30.1) 5,228.2 5,242.2 Provision for (Release of) Credit Losses (3.3) 3.8 16.8 3.2 — — — — 13.5 7.0 Noninterest Expense 2,459.7 2,269.4 1,402.4 1,333.2 33.6 56.7 — — 3,895.7 3,659.3 Income before Income Taxes 656.6 785.0 744.7 888.9 (42.8) (67.9) (39.5) (30.1) 1,319.0 1,575.9 Provision for Income Taxes 167.4 194.0 207.5 248.6 (10.6) (16.9) (39.5) (30.1) 324.8 395.6 Net Income $ 489.2 $ 591.0 $ 537.2 $ 640.3 $ (32.2) $ (51.0) $ — $ — $ 994.2 $ 1,180.3 Percentage of Consolidated Net Income 49 % 50 % 54 % 54 % (3) % (4) % N/A N/A 100 % 100 % Average Assets $ 110,380.4 $ 117,251.0 $ 34,311.2 $ 36,901.1 $ — $ — N/A N/A $ 144,691.6 $ 154,152.1 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)	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and 2022, and changes during the three and nine months then ended. TABLE 64: SUMMARY OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED SEPTEMBER 30, 2023 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES (1) NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at June 30, 2023 $ (1,229.4) $ 0.5 $ 189.2 $ (366.2) $ (1,405.9) Net Change 32.3 (0.4) 9.6 1.0 42.5 Balance at September 30, 2023 $ (1,197.1) $ 0.1 $ 198.8 $ (365.2) $ (1,363.4) (1) Includes net unrealized gains (losses) on debt securities transferred from AFS to HTM. Refer to Note 4—Securities for further information. NINE MONTHS ENDED SEPTEMBER 30, 2023 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES (1) 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 170.5 (1.1) 34.2 2.2 205.8 Balance at September 30, 2023 $ (1,197.1) $ 0.1 $ 198.8 $ (365.2) $ (1,363.4) (1) Includes net unrealized gains (losses) on debt securities transferred from AFS to HTM. Refer to Note 4—Securities for further information. THREE MONTHS ENDED SEPTEMBER 30, 2022 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES (1) NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at June 30, 2022 $ (1,294.7) $ 0.6 $ 137.6 $ (354.1) $ (1,510.6) Net Change (272.2) 2.1 20.2 (24.5) (274.4) Balance at September 30, 2022 $ (1,566.9) $ 2.7 $ 157.8 $ (378.6) $ (1,785.0) (1) Includes net unrealized gains (losses) on debt securities transferred from AFS to HTM. Refer to Note 4—Securities for further information. NINE MONTHS ENDED SEPTEMBER 30, 2022 (In Millions) NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES (1) NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2021 $ 107.1 $ (2.4) $ 155.2 $ (295.5) $ (35.6) Net Change (1,674.0) 5.1 2.6 (83.1) (1,749.4) Balance at September 30, 2022 $ (1,566.9) $ 2.7 $ 157.8 $ (378.6) $ (1,785.0) (1) Includes net unrealized gains (losses) on debt securities transferred from AFS to HTM. Refer to Note 4—Securities for further information.
Details of Changes in Accumulated Other Comprehensive Income (Loss)	TABLE 65: DETAILS OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED SEPTEMBER 30, 2023 2022 (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 $ 18.0 $ (5.6) $ 12.4 $ (385.6) $ 97.5 $ (288.1) Reclassification Adjustments for (Gains) Losses Included in Net Income: Interest Income on Debt Securities (1) 26.7 (6.8) 19.9 21.0 (5.3) 15.7 Net (Gains) Losses on Debt Securities (2) — — — 0.3 (0.1) 0.2 Net Change $ 44.7 $ (12.4) $ 32.3 $ (364.3) $ 92.1 $ (272.2) Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ 14.3 $ (3.6) $ 10.7 $ 2.2 $ (0.6) $ 1.6 Reclassification Adjustment for (Gains) Losses Included in Net Income (3) (14.9) 3.8 (11.1) 0.6 (0.1) 0.5 Net Change $ (0.6) $ 0.2 $ (0.4) $ 2.8 $ (0.7) $ 2.1 Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (89.2) $ 1.7 $ (87.5) $ (168.1) $ 3.9 $ (164.2) Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) (0.2) 0.1 (0.1) (2.0) 0.5 (1.5) Net Investment Hedge Gains (Losses) 129.9 (32.7) 97.2 248.4 (62.5) 185.9 Net Change $ 40.5 $ (30.9) $ 9.6 $ 78.3 $ (58.1) $ 20.2 Pension and Other Postretirement Benefit Adjustments Net Actuarial Gains (Losses) $ (0.2) $ — $ (0.2) $ (51.6) $ 13.0 $ (38.6) Reclassification Adjustment for (Gains) Losses Included in Net Income (4) Amortization of Net Actuarial Loss 1.6 (0.4) 1.2 1.9 (0.4) 1.5 Amortization of Prior Service Cost (Credit) — — — (0.2) 0.1 (0.1) Settlement Loss — — — 17.0 (4.3) 12.7 Net Change $ 1.4 $ (0.4) $ 1.0 $ (32.9) $ 8.4 $ (24.5) Total Net Change $ 86.0 $ (43.5) $ 42.5 $ (316.1) $ 41.7 $ (274.4) NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 (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 $ 158.6 $ (42.0) $ 116.6 $ (2,288.3) $ 587.4 $ (1,700.9) Reclassification Adjustments for (Gains) Losses Included in Net Income: Interest Income on Debt Securities (1) 79.0 (19.9) 59.1 35.7 (9.0) 26.7 Net (Gains) Losses on Debt Securities (2) (6.9) 1.7 (5.2) 0.3 (0.1) 0.2 Net Change $ 230.7 $ (60.2) $ 170.5 $ (2,252.3) $ 578.3 $ (1,674.0) Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ 16.2 $ (4.1) $ 12.1 $ 3.0 $ (0.8) $ 2.2 Reclassification Adjustment for (Gains) Losses Included in Net Income (3) (17.7) 4.5 (13.2) 3.8 (0.9) 2.9 Net Change $ (1.5) $ 0.4 $ (1.1) $ 6.8 $ (1.7) $ 5.1 Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (15.7) $ 1.2 $ (14.5) $ (382.1) $ 4.5 $ (377.6) Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) (1.8) 0.5 (1.3) (3.8) 1.0 (2.8) Net Investment Hedge Gains (Losses) 66.8 (16.8) 50.0 512.1 (129.1) 383.0 Net Change $ 49.3 $ (15.1) $ 34.2 $ 126.2 $ (123.6) $ 2.6 Pension and Other Postretirement Benefit Adjustments Net Actuarial Gains (Losses) $ (1.5) $ 0.1 $ (1.4) $ (165.2) $ 41.2 $ (124.0) Reclassification Adjustment for (Gains) Losses Included in Net Income (4) Amortization of Net Actuarial Loss 4.8 (1.2) 3.6 17.1 (4.2) 12.9 Amortization of Prior Service Cost (Credit) — — — (0.7) 0.2 (0.5) Settlement Loss — — — 38.0 (9.5) 28.5 Net Change $ 3.3 $ (1.1) $ 2.2 $ (110.8) $ 27.7 $ (83.1) Total Net Change $ 281.8 $ (76.0) $ 205.8 $ (2,230.1) $ 480.7 $ (1,749.4) (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. Refer to Note 4—Securities for further information. (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)	9 Months Ended
	Sep. 30, 2023
Earnings Per Share [Abstract]
Net Income per Common Share	The computations of net income per common share are presented in the following table. TABLE 66: NET INCOME PER COMMON SHARE THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, ($ In Millions Except Per Common Share Information) 2023 2022 2023 2022 Basic Net Income Per Common Share Average Number of Common Shares Outstanding 207,021,554 208,400,135 207,611,420 208,271,070 Net Income $ 327.8 $ 394.8 $ 994.2 $ 1,180.3 Less: Dividends on Preferred Stock 16.2 16.2 37.1 37.1 Net Income Applicable to Common Stock 311.6 378.6 957.1 1,143.2 Less: Earnings Allocated to Participating Securities 3.1 3.2 9.7 9.5 Earnings Allocated to Common Shares Outstanding 308.5 375.4 947.4 1,133.7 Basic Net Income Per Common Share $ 1.49 $ 1.80 $ 4.56 $ 5.44 Diluted Net Income Per Common Share Average Number of Common Shares Outstanding 207,021,554 208,400,135 207,611,420 208,271,070 Plus: Dilutive Effect of Share-based Compensation 231,438 488,437 316,300 587,906 Average Common and Potential Common Shares 207,252,992 208,888,572 207,927,720 208,858,976 Earnings Allocated to Common and Potential Common Shares $ 308.5 $ 375.4 $ 947.3 $ 1,133.7 Diluted Net Income Per Common Share 1.49 1.80 4.56 5.43

Revenue from Contracts with C_2

Revenue from Contracts with Clients (Tables)	9 Months Ended
	Sep. 30, 2023
Revenue from Contract with Customer [Abstract]
Revenue Disaggregation	The following table presents revenues disaggregated by major revenue source. TABLE 67: REVENUE DISAGGREGATION THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Noninterest Income Trust, Investment and Other Servicing Fees Custody and Fund Administration $ 459.0 $ 435.0 $ 1,358.7 $ 1,383.4 Investment Management and Advisory 574.1 565.3 1,673.4 1,765.8 Securities Lending 20.7 21.7 61.3 62.2 Other 58.1 56.7 178.4 179.1 Total Trust, Investment and Other Servicing Fees $ 1,111.9 $ 1,078.7 $ 3,271.8 $ 3,390.5 Other Noninterest Income Foreign Exchange Trading Income $ 51.8 $ 64.7 $ 154.9 $ 223.2 Treasury Management Fees 7.5 9.3 23.8 31.0 Security Commissions and Trading Income 30.9 32.1 101.7 101.1 Other Operating Income 68.2 57.3 170.2 144.0 Investment Security Gains (Losses), net — (0.3) 6.9 (0.3) Total Other Noninterest Income $ 158.4 $ 163.1 $ 457.5 $ 499.0 Total Noninterest Income $ 1,270.3 $ 1,241.8 $ 3,729.3 $ 3,889.5
Contract Balances	The table below represents receivables balances from contracts with clients, which are included in Other Assets on the consolidated balance sheets, at September 30, 2023 and December 31, 2022. TABLE 68: CLIENT RECEIVABLES (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Trust Fees Receivable, net (1) $ 903.0 $ 882.5 Other 57.4 55.4 Total Client Receivables $ 960.4 $ 937.9 (1) Trust Fees Receivable is net of a $14.6 million and $13.5 million fee receivable allowance as of September 30, 2023 and December 31, 2022, respectively.

Net Interest Income (Tables)

Net Interest Income (Tables)	9 Months Ended
	Sep. 30, 2023
Banking and Thrift, Interest [Abstract]
Net Interest Income	The components of Net Interest Income were as follows. TABLE 69: NET INTEREST INCOME THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Interest Income Federal Reserve and Other Central Bank Deposits $ 352.1 $ 135.4 $ 1,128.0 $ 212.2 Interest-Bearing Due from and Deposits with Banks (1) 34.9 14.5 95.2 23.6 Federal Funds Sold — — 0.3 — Securities Purchased under Agreements to Resell 463.9 30.5 874.1 38.4 Securities — Taxable 402.4 237.0 1,106.5 599.7 — Nontaxable (2) 0.3 0.4 1.0 1.1 Loans and Leases 664.2 379.8 1,881.6 827.4 Other Interest-Earning Assets (3) 17.2 1.7 38.7 5.2 Total Interest Income $ 1,935.0 $ 799.3 $ 5,125.4 $ 1,707.6 Interest Expense Deposits $ 716.6 $ 177.3 $ 1,914.7 $ 184.6 Federal Funds Purchased 77.5 9.9 205.2 12.7 Securities Sold Under Agreements to Repurchase 454.0 25.5 843.5 31.8 Other Borrowings 154.8 35.7 446.3 47.2 Senior Notes 44.1 28.6 125.4 57.1 Long-Term Debt 31.8 9.3 91.4 21.5 Total Interest Expense $ 1,478.8 $ 286.3 $ 3,626.5 $ 354.9 Net Interest Income $ 456.2 $ 513.0 $ 1,498.9 $ 1,352.7 (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)	9 Months Ended
	Sep. 30, 2023
Other Income and Expenses [Abstract]
Components of Other Operating Income	The components of Other Operating Income were as follows. TABLE 70: OTHER OPERATING INCOME THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Loan Service Fees $ 21.2 $ 17.8 $ 61.3 $ 52.6 Banking Service Fees 15.0 12.2 40.8 37.8 Bank Owned Life Insurance 17.3 17.3 51.0 44.0 Other Income (1) 14.7 10.0 17.1 9.6 Total Other Operating Income $ 68.2 $ 57.3 $ 170.2 $ 144.0 (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)	9 Months Ended
	Sep. 30, 2023
Other Income and Expenses [Abstract]
Summary of other operating expenses	The components of Other Operating Expense were as follows. TABLE 71: OTHER OPERATING EXPENSE THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, ($ In Millions) 2023 2022 2023 2022 Business Promotion $ 16.2 $ 20.1 $ 53.5 $ 49.0 Staff Related 11.0 7.8 27.7 16.9 FDIC Insurance Premiums 8.3 3.7 21.1 14.1 Charitable Contributions 3.8 5.0 11.3 12.1 Other Expenses 59.2 45.4 182.5 159.5 Total Other Operating Expense $ 98.5 $ 82.0 $ 296.1 $ 251.6

Pension (Tables)

Pension (Tables)	9 Months Ended
	Sep. 30, 2023
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 and nine months ended September 30, 2023 and 2022. TABLE 72: NET PERIODIC PENSION EXPENSE (BENEFIT) U.S. QUALIFIED PLAN THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Service Cost $ 11.5 $ 11.1 $ 34.5 $ 37.5 Interest Cost 13.5 12.5 40.5 33.1 Expected Return on Plan Assets (25.3) (21.9) (75.9) (62.3) Amortization Net Actuarial Loss 0.4 — 1.2 11.4 Prior Service Cost (Credit) — — — (0.1) Net Periodic Pension Expense $ 0.1 $ 1.7 $ 0.3 $ 19.6 Settlement Expense — 17.0 — 37.3 Total Pension Expense $ 0.1 $ 18.7 $ 0.3 $ 56.9 NON-U.S. PENSION PLANS THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Service Cost $ 0.4 $ 0.4 $ 1.1 $ 1.3 Interest Cost 1.2 0.6 3.6 1.9 Expected Return on Plan Assets (1.6) (0.7) (4.7) (2.2) Amortization Net Actuarial (Gain) Loss (0.1) 0.2 (0.3) 0.6 Net Periodic Pension (Benefit) Expense $ (0.1) $ 0.5 $ (0.3) $ 1.6 Settlement Expense — — — 0.7 Total Pension (Benefit) Expense $ (0.1) $ 0.5 $ (0.3) $ 2.3 U.S. NON-QUALIFIED PLAN THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Service Cost $ 1.2 $ 1.4 $ 3.6 $ 4.2 Interest Cost 1.3 1.0 3.9 3.0 Amortization Net Actuarial Loss 1.3 1.8 3.9 5.4 Net Periodic Pension Expense $ 3.8 $ 4.2 $ 11.4 $ 12.6

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	9 Months Ended
	Sep. 30, 2023
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 and nine months ended September 30, 2023 and 2022. TABLE 73: TOTAL COMPENSATION EXPENSE FOR SHARE-BASED PAYMENT ARRANGEMENTS THREE MONTHS ENDED SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, (In Millions) 2023 2022 2023 2022 Restricted Stock Unit Awards $ 14.7 $ 13.9 $ 80.5 $ 83.4 Performance Stock Units 1.8 0.9 17.8 21.4 Total Share-Based Compensation Expense 16.5 14.8 98.3 104.8 Tax Benefits Recognized $ 4.2 $ 3.7 $ 24.7 $ 26.3

Variable Interest Entities (Tab

Variable Interest Entities (Tables)	9 Months Ended
	Sep. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Variable Interest Entities	TABLE 74: SUMMARY OF UNCONSOLIDATED TAX CREDIT STRUCTURES (In Millions) SEPTEMBER 30, 2023 DECEMBER 31, 2022 Investment Carrying Amount Affordable Housing $ 640.1 $ 635.9 Other Community Development 254.4 268.4 Total Investment Carrying Amount (1) $ 894.5 $ 904.3 Unfunded Commitments Affordable Housing $ 205.5 $ 218.9 Other Community Development — — Total Unfunded Commitments (2) $ 205.5 $ 218.9 (1) As of September 30, 2023 and December 31, 2022, $861.2 million and $867.2 million are VIEs, respectively. (2) As of September 30, 2023 and December 31, 2022, $198.5 million and $210.1 million relate to undrawn commitments on VIEs, respectively.

Commitments and Contingent Li_2

Commitments and Contingent Liabilities (Tables)	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022. TABLE 75: SUMMARY OF OFF-BALANCE SHEET FINANCIAL INSTRUMENTS SEPTEMBER 30, 2023 DECEMBER 31, 2022 ($ In Millions) ONE YEAR AND LESS OVER ONE YEAR TOTAL ONE YEAR AND LESS OVER ONE YEAR TOTAL Undrawn Commitments (1) $ 12,409.2 $ 18,452.1 $ 30,861.3 $ 13,639.2 $ 17,321.4 $ 30,960.6 Standby Letters of Credit and Financial Guarantees (2)(3) 62,939.0 375.8 63,314.8 17,553.0 409.9 17,962.9 Commercial Letters of Credit 24.5 1.3 25.8 25.4 1.3 26.7 Securities Lent with Indemnification 141,392.4 — 141,392.4 130,311.0 — 130,311.0 Unsettled Reverse Repurchase Agreements 19,127.3 — 19,127.3 496.8 — 496.8 Total Off-Balance Sheet Financial Instruments $ 235,892.4 $ 18,829.2 $ 254,721.6 $ 162,025.4 $ 17,732.6 $ 179,758.0 (1) These amounts exclude $222.5 million and $266.6 million of commitments participated to others at September 30, 2023 and December 31, 2022, respectively. (2) These amounts include $33.4 million and $35.1 million of standby letters of credit secured by cash deposits or participated to others as of September 30, 2023 and December 31, 2022, respectively. (3) These amounts include a $61.4 billion and $16.3 billion guarantee to the Fixed Income Clearing Corporation (FICC) under the sponsored member program, without taking into consideration the related collateral, as of September 30, 2023 and December 31, 2022, respectively. Northern Trust became a sponsored member during the third quarter of 2021.

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022. TABLE 76: NOTIONAL AND FAIR VALUES OF DERIVATIVE FINANCIAL INSTRUMENTS SEPTEMBER 30, 2023 DECEMBER 31, 2022 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 $ 5,566.1 $ 82.8 $ 43.2 $ 4,622.0 $ 58.5 $ 32.7 Foreign Exchange Contracts Cash Flow Hedges 934.4 50.5 — 150.9 7.4 5.7 Net Investment Hedges 3,820.0 126.8 1.2 3,765.0 283.5 12.7 Total Derivatives Designated as Hedging under GAAP $ 10,320.5 $ 260.1 $ 44.4 $ 8,537.9 $ 349.4 $ 51.1 Derivatives Not Designated as Hedging under GAAP Non-Designated Risk Management Derivatives Foreign Exchange Contracts $ 50.5 $ 0.7 $ 0.1 $ 55.9 $ 0.1 $ 0.1 Other Financial Derivatives (3) 768.1 — 28.9 717.7 0.3 34.8 Total Non-Designated Risk Management Derivatives $ 818.6 $ 0.7 $ 29.0 $ 773.6 $ 0.4 $ 34.9 Client-Related and Trading Derivatives Foreign Exchange Contracts $ 311,789.1 $ 2,871.1 $ 2,818.9 $ 288,994.6 $ 3,219.1 $ 3,169.0 Interest Rate Contracts 12,080.7 281.1 424.1 12,378.2 163.5 399.1 Total Client-Related and Trading Derivatives $ 323,869.8 $ 3,152.2 $ 3,243.0 $ 301,372.8 $ 3,382.6 $ 3,568.1 Total Derivatives Not Designated as Hedging under GAAP $ 324,688.4 $ 3,152.9 $ 3,272.0 $ 302,146.4 $ 3,383.0 $ 3,603.0 Total Gross Derivatives $ 335,008.9 $ 3,413.0 $ 3,316.4 $ 310,684.3 $ 3,732.4 $ 3,654.1 Less: Netting (4) 1,553.1 2,409.9 2,810.7 1,865.9 Total Derivative Financial Instruments $ 1,859.9 $ 906.5 $ 921.7 $ 1,788.2 (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) This line includes swaps related to sales of certain Visa Class B common shares and total return swap contracts. (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- and nine-month periods ended September 30, 2023 and 2022. TABLE 77: 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 SEPTEMBER 30, 2023 2022 2023 2022 2023 2022 Total amounts on the consolidated statements of income $ 1,935.0 $ 799.3 $ 1,478.8 $ 286.3 $ 68.2 $ 57.3 Gains (Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives 14.1 32.3 (41.8) (119.9) — — Recognized on hedged items (14.1) (32.3) 41.8 119.9 — — Amounts related to interest settlements on derivatives 11.1 (4.0) (24.9) (6.9) — — Total gains (losses) recognized on fair value hedges $ 11.1 $ (4.0) $ (24.9) $ (6.9) $ — $ — Gains (Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gains (losses) reclassified from AOCI to net income $ 14.6 $ — $ — $ — $ 0.3 $ (0.6) Total gains (losses) reclassified from AOCI to net income on cash flow hedges $ 14.6 $ — $ — $ — $ 0.3 $ (0.6) (In Millions) INTEREST INCOME INTEREST EXPENSE OTHER OPERATING INCOME NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 2023 2022 Total amounts on the consolidated statements of income $ 5,125.4 $ 1,707.6 $ 3,626.5 $ 354.9 $ 170.2 $ 144.0 Gains (Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives 0.6 90.0 (42.5) (373.6) — — Recognized on hedged items (0.6) (90.0) 42.5 373.6 — — Amounts related to interest settlements on derivatives 34.7 (13.3) (65.9) 18.0 — — Total gains (losses) recognized on fair value hedges $ 34.7 $ (13.3) $ (65.9) $ 18.0 $ — $ — Gains (Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gains (losses) reclassified from AOCI to net income $ 15.8 $ 0.6 $ — $ — $ 1.9 $ (4.4) Total gains (losses) reclassified from AOCI to net income on cash flow hedges $ 15.8 $ 0.6 $ — $ — $ 1.9 $ (4.4)
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 September 30, 2023 and December 31, 2022. TABLE 78: HEDGED ITEMS IN FAIR VALUE HEDGES SEPTEMBER 30, 2023 DECEMBER 31, 2022 (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) $ 2,631.6 $ (55.7) $ 1,820.8 $ (60.2) Senior Notes and Long-Term Subordinated Debt 2,407.6 (336.5) 2,746.2 (294.0) (1) The cumulative hedge accounting basis adjustment includes $2.2 million related to discontinued hedging relationships of AFS debt securities as of September 30, 2023. There are no amounts related to discontinued hedging relationships in the cumulative hedge accounting basis adjustment of senior notes and long-term debt as of September 30, 2023. (2) The cumulative hedge accounting basis adjustment includes $7.3 million related to discontinued hedging relationships of AFS debt securities as of December 31, 2022. There were no amounts related to discontinued hedging relationships in the cumulative hedge accounting basis adjustment of senior notes and long-term debt as of December 31, 2022. (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 nine months ended September 30, 2023 and 2022 for derivative instruments not designated as hedges under GAAP. TABLE 79: 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 SEPTEMBER 30, NINE MONTHS ENDED SEPTEMBER 30, 2023 2022 2023 2022 Non-designated risk management derivatives Foreign Exchange Contracts Other Operating Income $ 1.4 $ (0.6) $ 2.9 $ (2.0) Other Financial Derivatives (1) Other Operating Income 2.4 0.7 (18.3) (9.4) Gains (Losses) from non-designated risk management derivatives $ 3.8 $ 0.1 $ (15.4) $ (11.4) Client-related and trading derivatives Foreign Exchange Contracts Foreign Exchange Trading Income $ 51.8 $ 64.7 $ 154.9 $ 223.2 Interest Rate Contracts Security Commissions and Trading Income 1.2 2.9 8.1 7.1 Gains from client-related and trading derivatives $ 53.0 $ 67.6 $ 163.0 $ 230.3 Total gains from derivatives not designated as hedging under GAAP $ 56.8 $ 67.7 $ 147.6 $ 218.9 (1) This line includes swaps related to the sale of certain Visa Class B common shares and total return swap contracts.

Securities Sold Under Agreeme_2

Securities Sold Under Agreements to Repurchase (Tables)	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022. TABLE 80: REPURCHASE AGREEMENTS ACCOUNTED FOR AS SECURED BORROWINGS REMAINING CONTRACTUAL MATURITY OF THE AGREEMENTS SEPTEMBER 30, 2023 DECEMBER 31, 2022 ($ In Millions) OVERNIGHT AND CONTINUOUS U.S. Treasury and Agency Securities $ 545.9 $ 567.2 Total Borrowings 545.9 567.2 Net Amount of Recognized Liabilities for Repurchase Agreements in Note 23 545.9 567.2

Offsetting of Assets and Liab_2

Offsetting of Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2023
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 September 30, 2023 and December 31, 2022. TABLE 81: OFFSETTING OF DERIVATIVE ASSETS AND SECURITIES PURCHASED UNDER AGREEMENTS TO RESELL SEPTEMBER 30, 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 Over the Counter (OTC) $ 2,106.8 $ 1,266.6 $ 840.2 $ 14.3 $ 825.9 Interest Rate Swaps OTC 363.9 286.5 77.4 — 77.4 Total Derivatives Subject to a Master Netting Arrangement 2,470.7 1,553.1 917.6 14.3 903.3 Total Derivatives Not Subject to a Master Netting Arrangement 942.3 — 942.3 — 942.3 Total Derivatives 3,413.0 1,553.1 1,859.9 14.3 1,845.6 Securities Purchased under Agreements to Resell (2) $ 50,143.2 $ 49,758.9 $ 384.3 $ 384.3 $ — DECEMBER 31, 2022 (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 $ 2,928.9 $ 2,666.4 $ 262.5 $ 5.0 $ 257.5 Interest Rate Swaps OTC 217.6 144.3 73.3 — 73.3 Interest Rate Swaps Exchange Cleared 4.4 — 4.4 — 4.4 Other Financial Derivative 0.3 — 0.3 — 0.3 Total Derivatives Subject to a Master Netting Arrangement 3,151.2 2,810.7 340.5 5.0 335.5 Total Derivatives Not Subject to a Master Netting Arrangement 581.2 — 581.2 — 581.2 Total Derivatives 3,732.4 2,810.7 921.7 5.0 916.7 Securities Purchased under Agreements to Resell (2) $ 12,494.2 $ 11,423.9 $ 1,070.3 $ 1,070.3 $ — (1) Derivative assets are reported in Other Assets on the consolidated balance sheets. Other Assets (excluding derivative assets) totaled $10.7 billion and $8.9 billion as of September 30, 2023 and December 31, 2022, 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 September 30, 2023 and December 31, 2022.
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 September 30, 2023 and December 31, 2022. TABLE 82: OFFSETTING OF DERIVATIVE LIABILITIES AND SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE SEPTEMBER 30, 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 $ 2,527.7 $ 2,380.6 $ 147.1 $ — $ 147.1 Interest Rate Swaps OTC 467.3 2.1 465.2 — 465.2 Other Financial Derivatives 28.9 27.2 1.7 — 1.7 Total Derivatives Subject to a Master Netting Arrangement 3,023.9 2,409.9 614.0 — 614.0 Total Derivatives Not Subject to a Master Netting Arrangement 292.5 — 292.5 — 292.5 Total Derivatives 3,316.4 2,409.9 906.5 — 906.5 Securities Sold under Agreements to Repurchase (2) $ 50,304.8 $ 49,758.9 $ 545.9 $ 545.9 $ — DECEMBER 31, 2022 (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 $ 2,082.3 $ 1,826.7 $ 255.6 $ — $ 255.6 Interest Rate Swaps OTC 426.5 5.9 420.6 — 420.6 Interest Rate Swaps Exchange Cleared 5.3 — 5.3 — 5.3 Other Financial Derivatives 34.8 33.3 1.5 — 1.5 Total Derivatives Subject to a Master Netting Arrangement 2,548.9 1,865.9 683.0 — 683.0 Total Derivatives Not Subject to a Master Netting Arrangement 1,105.2 — 1,105.2 — 1,105.2 Total Derivatives 3,654.1 1,865.9 1,788.2 — 1,788.2 Securities Sold under Agreements to Repurchase (2) $ 11,991.1 $ 11,423.9 $ 567.2 $ 567.2 $ — (1) Derivative liabilities are reported in Other Liabilities on the consolidated balance sheets. Other Liabilities (excluding derivative liabilities) totaled $3.7 billion and $3.2 billion as of September 30, 2023 and December 31, 2022, 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 September 30, 2023 and December 31, 2022.

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) shares in Millions, $ in Millions	Sep. 30, 2023 USD ($) security	Dec. 31, 2022 USD ($) 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	$ 24,342.1	$ 26,699.9
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	1,009	1,163
Available for Sale	$ 21,500	$ 24,000
LEVEL 3 | Fair Value, Measurements, Nonrecurring | Measurement Input, Discount Rate
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 | Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input		0.150
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	0.200	0.172
LEVEL 3 | Fair Value, Measurements, Nonrecurring | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 3.8

Fair Value Measurements (Level

Fair Value Measurements (Level 3 Significant Unobservable Inputs) (Details) $ in Millions	Sep. 30, 2023 USD ($) month	Dec. 31, 2022 USD ($) month
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities | $	$ 906.5	$ 1,788.2
Swap | Fair Value, Measurements, Recurring | LEVEL 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities | $	$ 28.9	$ 34.8
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	1.60
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	0.1015	0.0853
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	16	20
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	12	12
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	30	33

Fair Value Measurements (Recurr

Fair Value Measurements (Recurring Basis Hierarchy Leveling) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	$ 24,342.1	$ 26,699.9
Derivative Assets	3,413	3,732.4
NETTING	(1,553.1)	(2,810.7)
Derivative Assets	1,859.9	921.7
Derivative Liabilities	3,316.4	3,654.1
NETTING	(2,409.9)	(1,865.9)
Derivative Liabilities	906.5	1,788.2
Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING		0
Cross Product Collateral Adjustment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(287)	(1,100)
NETTING	(1,100)	(195.3)
U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,879.4	2,747.4
Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	282.1	787.6
Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	11,656.8	11,545.2
Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	246.9	360
Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	380.9	1,747.6
Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	280.4	388.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,959.8	2,479.4
Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	4,771.5	5,256.2
Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	884.3	1,387.8
LEVEL 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	21,500	24,000
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	24,342.1	26,699.9
Trading Account	0.1	95.2
Total Available for Sale and Trading Debt Securities	24,342.2	26,795.1
Fair Value, Measurements, Recurring | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,879.4	2,747.4
Fair Value, Measurements, Recurring | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	282.1	787.6
Fair Value, Measurements, Recurring | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	11,656.8	11,545.2
Fair Value, Measurements, Recurring | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	246.9	360
Fair Value, Measurements, Recurring | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	380.9	1,747.6
Fair Value, Measurements, Recurring | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	280.4	388.7
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	2,959.8	2,479.4
Fair Value, Measurements, Recurring | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	4,771.5	5,256.2
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	884.3	1,387.8
Fair Value, Measurements, Recurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money Market Investment	95
NETTING	(1,553.1)	(2,810.7)
Derivative Assets	1,859.9	921.7
Fair Value, Measurements, Recurring | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(1,266.6)	(2,666.4)
Derivative Assets	1,782.5	843.7
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(286.5)	(144.3)
Derivative Assets	77.4	77.7
Fair Value, Measurements, Recurring | Other Assets | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	0	0
Derivative Assets	0	0.3
Fair Value, Measurements, Recurring | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(2,409.9)	(1,865.9)
Derivative Liabilities	906.5	1,788.2
Fair Value, Measurements, Recurring | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(2,380.6)	(1,826.7)
Derivative Liabilities	439.6	1,360.8
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(2.1)	(5.9)
Derivative Liabilities	465.2	425.9
Fair Value, Measurements, Recurring | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(27.2)	(33.3)
Derivative Liabilities	1.7	1.5
Fair Value, Measurements, Recurring | LEVEL 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,879.4	2,747.4
Trading Account	0	95
Total Available for Sale and Trading Debt Securities	2,879.4	2,842.4
Fair Value, Measurements, Recurring | LEVEL 1 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,879.4	2,747.4
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
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 Assets | Other Financial Derivatives
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	21,462.7	23,952.5
Trading Account	0.1	0.2
Total Available for Sale and Trading Debt Securities	21,462.8	23,952.7
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	282.1	787.6
Fair Value, Measurements, Recurring | LEVEL 2 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	11,656.8	11,545.2
Fair Value, Measurements, Recurring | LEVEL 2 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	246.9	360
Fair Value, Measurements, Recurring | LEVEL 2 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	380.9	1,747.6
Fair Value, Measurements, Recurring | LEVEL 2 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	280.4	388.7
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	2,959.8	2,479.4
Fair Value, Measurements, Recurring | LEVEL 2 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	4,771.5	5,256.2
Fair Value, Measurements, Recurring | LEVEL 2 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	884.3	1,387.8
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Money Market Investment	0
Derivative Assets	3,413	3,732.4
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	3,049.1	3,510.1
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	363.9	222
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0.3
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	3,287.5	3,619.3
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	2,820.2	3,187.5
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	467.3	431.8
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	0
Total Available for Sale and Trading Debt Securities	0	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
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 Assets | Other Financial Derivatives
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	28.9	34.8
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	$ 28.9	$ 34.8

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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value liabilities beginning balance	$ 36.4	$ 31.1	$ 34.8	$ 37.5
Total (Gains) Losses:
Included in Earnings	(2.4)	1.1	16.1	11.2
Purchases, Issues, Sales, and Settlements
Settlements	(5.1)	(4.6)	(22)	(21.1)
Fair value liabilities ending balance	$ 28.9	$ 27.6	$ 28.9	$ 27.6

Fair Value Measurements (Nonrec

Fair Value Measurements (Nonrecurring Basis Significant Unobservable Inputs) (Details) - Fair Value, Measurements, Nonrecurring - LEVEL 3 $ in Millions	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FAIR VALUE	$ 3.8
Measurement Input, Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.200
Measurement Input, Discount Rate | Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input		0.150
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	0.200	0.172
Loans | Measurement Input, Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FAIR VALUE	$ 3.8	$ 6.6

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
ASSETS
Cash and Due from Banks	$ 4,955,700,000	$ 4,654,200,000
Federal Reserve and Other Central Bank Deposits	32,316,800,000	40,030,400,000
Interest-Bearing Deposits with Banks	2,122,500,000	1,941,100,000
Securities Purchased under Agreements to Resell	384,300,000	1,070,300,000
Debt Securities - Held to Maturity	22,449,700,000	22,879,300,000
Deposits
Savings Certificates and Other Time	4,038,600,000	1,981,300,000
Non U.S. Offices Interest-Bearing	60,826,900,000	65,481,900,000
Federal Funds Purchased	5,539,300,000	1,896,900,000
Securities Sold Under Agreements to Repurchase	545,900,000	567,200,000
Other Borrowings	6,870,900,000	7,592,300,000
Senior Notes	2,688,900,000	2,724,200,000
Unfunded Commitments	0	0
BOOK VALUE
ASSETS
Cash and Due from Banks	4,955,700,000	4,654,200,000
Federal Reserve and Other Central Bank Deposits	32,316,800,000	40,030,400,000
Interest-Bearing Deposits with Banks	2,122,500,000	1,941,100,000
Federal Funds Sold		32,000,000
Securities Purchased under Agreements to Resell	384,300,000	1,070,300,000
Debt Securities - Held to Maturity	24,920,400,000	25,036,100,000
Loans
Held for Investment	43,410,200,000	42,749,000,000
Other Assets	1,502,100,000	1,476,900,000
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	45,300,400,000	56,468,900,000
Savings Certificates and Other Time	4,038,600,000	1,981,300,000
Non U.S. Offices Interest-Bearing	60,826,900,000	65,481,900,000
Federal Funds Purchased	5,539,300,000	1,896,900,000
Securities Sold Under Agreements to Repurchase	545,900,000	567,200,000
Other Borrowings	6,870,900,000	7,592,300,000
Senior Notes	2,688,900,000	2,724,200,000
Long-Term Debt	4,060,700,000	2,066,200,000
Unfunded Commitments	205,500,000	218,900,000
Other Liabilities	89,500,000	73,200,000
TOTAL ESTIMATED FAIR VALUE
ASSETS
Cash and Due from Banks	4,955,700,000	4,654,200,000
Federal Reserve and Other Central Bank Deposits	32,316,800,000	40,030,400,000
Interest-Bearing Deposits with Banks	2,122,500,000	1,941,100,000
Federal Funds Sold		32,000,000
Securities Purchased under Agreements to Resell	384,300,000	1,070,300,000
Debt Securities - Held to Maturity	22,449,700,000	22,879,300,000
Loans
Held for Investment	43,384,400,000	42,636,500,000
Other Assets	1,485,400,000	1,460,400,000
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	45,300,400,000	56,468,900,000
Savings Certificates and Other Time	4,070,400,000	1,976,100,000
Non U.S. Offices Interest-Bearing	60,826,900,000	65,481,900,000
Federal Funds Purchased	5,539,300,000	1,896,900,000
Securities Sold Under Agreements to Repurchase	545,900,000	567,200,000
Other Borrowings	6,888,100,000	7,592,800,000
Senior Notes	2,646,600,000	2,729,800,000
Long-Term Debt	4,026,100,000	2,110,700,000
Unfunded Commitments	205,500,000	218,900,000
Other Liabilities	89,500,000	73,200,000
TOTAL ESTIMATED FAIR VALUE | LEVEL 1
ASSETS
Cash and Due from Banks	4,955,700,000	4,654,200,000
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Federal Funds Sold		0
Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	50,000,000
Loans
Held for Investment	0	0
Other Assets	89,400,000	94,700,000
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	45,300,400,000	56,468,900,000
Savings Certificates and Other Time	0	0
Non U.S. Offices Interest-Bearing	0	0
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	32,316,800,000	40,030,400,000
Interest-Bearing Deposits with Banks	2,122,500,000	1,941,100,000
Federal Funds Sold		32,000,000
Securities Purchased under Agreements to Resell	384,300,000	1,070,300,000
Debt Securities - Held to Maturity	22,449,700,000	22,829,300,000
Loans
Held for Investment	0	0
Other Assets	1,396,000,000	1,365,700,000
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0	0
Savings Certificates and Other Time	4,070,400,000	1,976,100,000
Non U.S. Offices Interest-Bearing	60,826,900,000	65,481,900,000
Federal Funds Purchased	5,539,300,000	1,896,900,000
Securities Sold Under Agreements to Repurchase	545,900,000	567,200,000
Other Borrowings	6,888,100,000	7,592,800,000
Senior Notes	2,646,600,000	2,729,800,000
Long-Term Debt	4,026,100,000	2,110,700,000
Unfunded Commitments	205,500,000	218,900,000
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
Federal Funds Sold		0
Securities Purchased under Agreements to Resell	0	0
Debt Securities - Held to Maturity	0	0
Loans
Held for Investment	43,384,400,000	42,636,500,000
Other Assets	0	0
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0	0
Savings Certificates and Other Time	0	0
Non U.S. Offices Interest-Bearing	0	0
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	$ 89,500,000	$ 73,200,000

Securities (Reconciliation of A

Securities (Reconciliation of Amortized Cost to Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Summary of Investment Holdings [Line Items]
AMORTIZED COST	$ 25,246.1	$ 27,760
GROSS UNREALIZED GAINS	9.1	7.7
GROSS UNREALIZED LOSSES	913.1	1,067.8
FAIR VALUE	24,342.1	26,699.9
U.S. Government
Summary of Investment Holdings [Line Items]
AMORTIZED COST	2,981.2	2,837.7
GROSS UNREALIZED GAINS	0	2.5
GROSS UNREALIZED LOSSES	101.8	92.8
FAIR VALUE	2,879.4	2,747.4
Obligations of States and Political Subdivisions
Summary of Investment Holdings [Line Items]
AMORTIZED COST	301.5	817.8
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	19.4	30.2
FAIR VALUE	282.1	787.6
Government Sponsored Agency
Summary of Investment Holdings [Line Items]
AMORTIZED COST	11,988.1	11,892.5
GROSS UNREALIZED GAINS	6.8	4.3
GROSS UNREALIZED LOSSES	338.1	351.6
FAIR VALUE	11,656.8	11,545.2
Non-U.S. Government
Summary of Investment Holdings [Line Items]
AMORTIZED COST	271	387.6
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	24.1	27.6
FAIR VALUE	246.9	360
Corporate Debt
Summary of Investment Holdings [Line Items]
AMORTIZED COST	397.9	1,774.3
GROSS UNREALIZED GAINS	0.1	0.2
GROSS UNREALIZED LOSSES	17.1	26.9
FAIR VALUE	380.9	1,747.6
Covered Bonds
Summary of Investment Holdings [Line Items]
AMORTIZED COST	292.2	403.1
GROSS UNREALIZED GAINS	0.1	0.3
GROSS UNREALIZED LOSSES	11.9	14.7
FAIR VALUE	280.4	388.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Summary of Investment Holdings [Line Items]
AMORTIZED COST	3,099.2	2,645.8
GROSS UNREALIZED GAINS	1	0.3
GROSS UNREALIZED LOSSES	140.4	166.7
FAIR VALUE	2,959.8	2,479.4
Other Asset-Backed
Summary of Investment Holdings [Line Items]
AMORTIZED COST	4,966.1	5,544.3
GROSS UNREALIZED GAINS	1	0
GROSS UNREALIZED LOSSES	195.6	288.1
FAIR VALUE	4,771.5	5,256.2
Commercial Mortgage-Backed
Summary of Investment Holdings [Line Items]
AMORTIZED COST	948.9	1,456.9
GROSS UNREALIZED GAINS	0.1	0.1
GROSS UNREALIZED LOSSES	64.7	69.2
FAIR VALUE	$ 884.3	$ 1,387.8

Securities (Remaining Maturity

Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Available for Sale - Amortized Cost
ONE YEAR OR LESS	$ 4,224.2
ONE TO FIVE YEARS	15,921.3
FIVE TO TEN YEARS	4,147.4
OVER TEN YEARS	953.2
AMORTIZED COST	25,246.1	$ 27,760
Available for Sale - Fair Value
ONE YEAR OR LESS	4,146.4
ONE TO FIVE YEARS	15,297.3
FIVE TO TEN YEARS	3,995.7
OVER TEN YEARS	902.7
FAIR VALUE	24,342.1	26,699.9
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	4,791.9
ONE TO FIVE YEARS	12,712.2
FIVE TO TEN YEARS	5,107.9
OVER TEN YEARS	2,308.4
Amortized Cost	24,920.4	25,036.1
Held to Maturity - Fair Value
ONE YEAR OR LESS	4,642.2
ONE TO FIVE YEARS	11,529.1
FIVE TO TEN YEARS	4,444.4
OVER TEN YEARS	1,834
Fair Value	22,449.7	22,879.3
U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	297.3
ONE TO FIVE YEARS	2,683.9
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
AMORTIZED COST	2,981.2	2,837.7
Available for Sale - Fair Value
ONE YEAR OR LESS	296.4
ONE TO FIVE YEARS	2,583
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
FAIR VALUE	2,879.4	2,747.4
Held to Maturity - Amortized Cost
Amortized Cost		50
Held to Maturity - Fair Value
Fair Value		50
Obligations of States and Political Subdivisions
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0
ONE TO FIVE YEARS	109.1
FIVE TO TEN YEARS	192.4
OVER TEN YEARS	0
AMORTIZED COST	301.5	817.8
Available for Sale - Fair Value
ONE YEAR OR LESS	0
ONE TO FIVE YEARS	102.8
FIVE TO TEN YEARS	179.3
OVER TEN YEARS	0
FAIR VALUE	282.1	787.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	58.1
ONE TO FIVE YEARS	988.1
FIVE TO TEN YEARS	1,187.1
OVER TEN YEARS	344.4
Amortized Cost	2,577.7	2,565.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	56.9
ONE TO FIVE YEARS	941.6
FIVE TO TEN YEARS	1,095.1
OVER TEN YEARS	306.2
Fair Value	2,399.8	2,415.5
Government Sponsored Agency
Available for Sale - Amortized Cost
ONE YEAR OR LESS	2,294.8
ONE TO FIVE YEARS	5,259.3
FIVE TO TEN YEARS	3,481.1
OVER TEN YEARS	952.9
AMORTIZED COST	11,988.1	11,892.5
Available for Sale - Fair Value
ONE YEAR OR LESS	2,250.7
ONE TO FIVE YEARS	5,113.8
FIVE TO TEN YEARS	3,389.9
OVER TEN YEARS	902.4
FAIR VALUE	11,656.8	11,545.2
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	859.7
ONE TO FIVE YEARS	3,105.8
FIVE TO TEN YEARS	3,408.4
OVER TEN YEARS	1,786
Amortized Cost	9,159.9	9,407.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	727.6
ONE TO FIVE YEARS	2,649.4
FIVE TO TEN YEARS	2,901.4
OVER TEN YEARS	1,475.9
Fair Value	7,754.3	8,331.7
Non-U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0
ONE TO FIVE YEARS	271
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
AMORTIZED COST	271	387.6
Available for Sale - Fair Value
ONE YEAR OR LESS	0
ONE TO FIVE YEARS	246.9
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
FAIR VALUE	246.9	360
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	2,341.3
ONE TO FIVE YEARS	1,338.1
FIVE TO TEN YEARS	32.4
OVER TEN YEARS	0
Amortized Cost	3,711.8	3,234
Held to Maturity - Fair Value
ONE YEAR OR LESS	2,337.5
ONE TO FIVE YEARS	1,221.1
FIVE TO TEN YEARS	26.7
OVER TEN YEARS	0
Fair Value	3,585.3	3,100.3
Corporate Debt
Available for Sale - Amortized Cost
ONE YEAR OR LESS	150.4
ONE TO FIVE YEARS	230.9
FIVE TO TEN YEARS	16.6
OVER TEN YEARS	0
AMORTIZED COST	397.9	1,774.3
Available for Sale - Fair Value
ONE YEAR OR LESS	148.2
ONE TO FIVE YEARS	218.8
FIVE TO TEN YEARS	13.9
OVER TEN YEARS	0
FAIR VALUE	380.9	1,747.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	96.2
ONE TO FIVE YEARS	528
FIVE TO TEN YEARS	14.9
OVER TEN YEARS	0
Amortized Cost	639.1	713.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	94.6
ONE TO FIVE YEARS	494.6
FIVE TO TEN YEARS	11.9
OVER TEN YEARS	0
Fair Value	601.1	667.9
Covered Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	141.6
ONE TO FIVE YEARS	150.6
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
AMORTIZED COST	292.2	403.1
Available for Sale - Fair Value
ONE YEAR OR LESS	140.1
ONE TO FIVE YEARS	140.3
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
FAIR VALUE	280.4	388.7
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	135.5
ONE TO FIVE YEARS	1,678.3
FIVE TO TEN YEARS	303.1
OVER TEN YEARS	0
Amortized Cost	2,116.9	2,530.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	132.6
ONE TO FIVE YEARS	1,582.7
FIVE TO TEN YEARS	260
OVER TEN YEARS	0
Fair Value	1,975.3	2,371.9
Certificates of Deposit
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	405.4
ONE TO FIVE YEARS	0
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
Amortized Cost	405.4	35.9
Held to Maturity - Fair Value
ONE YEAR OR LESS	405.5
ONE TO FIVE YEARS	0
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
Fair Value	405.5	35.9
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	569.8
ONE TO FIVE YEARS	2,465.3
FIVE TO TEN YEARS	64.1
OVER TEN YEARS	0
AMORTIZED COST	3,099.2	2,645.8
Available for Sale - Fair Value
ONE YEAR OR LESS	563
ONE TO FIVE YEARS	2,347.1
FIVE TO TEN YEARS	49.7
OVER TEN YEARS	0
FAIR VALUE	2,959.8	2,479.4
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	817
ONE TO FIVE YEARS	4,604.4
FIVE TO TEN YEARS	22.4
OVER TEN YEARS	0
Amortized Cost	5,443.8	5,703.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	810.2
ONE TO FIVE YEARS	4,216.8
FIVE TO TEN YEARS	17.8
OVER TEN YEARS	0
Fair Value	5,044.8	5,268.2
Other Asset-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	731.5
ONE TO FIVE YEARS	3,985.4
FIVE TO TEN YEARS	248.9
OVER TEN YEARS	0.3
AMORTIZED COST	4,966.1	5,544.3
Available for Sale - Fair Value
ONE YEAR OR LESS	711.3
ONE TO FIVE YEARS	3,815.4
FIVE TO TEN YEARS	244.5
OVER TEN YEARS	0.3
FAIR VALUE	4,771.5	5,256.2
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	43.8
ONE TO FIVE YEARS	93
FIVE TO TEN YEARS	109.8
OVER TEN YEARS	0
Amortized Cost	246.6	263.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	43.7
ONE TO FIVE YEARS	93.2
FIVE TO TEN YEARS	110.5
OVER TEN YEARS	0
Fair Value	247.4	262.7
Other
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	34.9
ONE TO FIVE YEARS	338.9
FIVE TO TEN YEARS	29.8
OVER TEN YEARS	178
Amortized Cost	581.6	532.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	33.6
ONE TO FIVE YEARS	292.8
FIVE TO TEN YEARS	21
OVER TEN YEARS	51.9
Fair Value	399.3	375.2
Commercial Mortgage-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	38.8
ONE TO FIVE YEARS	765.8
FIVE TO TEN YEARS	144.3
OVER TEN YEARS	0
AMORTIZED COST	948.9	1,456.9
Available for Sale - Fair Value
ONE YEAR OR LESS	36.7
ONE TO FIVE YEARS	729.2
FIVE TO TEN YEARS	118.4
OVER TEN YEARS	0
FAIR VALUE	884.3	$ 1,387.8
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
Held to Maturity - Fair Value
ONE YEAR OR LESS	0
ONE TO FIVE YEARS	36.9
FIVE TO TEN YEARS	0
OVER TEN YEARS	0
Fair Value	$ 36.9

Securities (Securities with Unr

Securities (Securities with Unrealized Losses) (Details) $ in Millions	Sep. 30, 2023 USD ($) Security	Dec. 31, 2022 USD ($) Security
FAIR VALUE
LESS THAN 12 MONTHS	$ 4,721	$ 15,665.4
12 MONTHS OR LONGER	17,339.1	5,769.4
TOTAL	22,060.1	21,434.8
UNREALIZED LOSSES
LESS THAN 12 MONTHS	32.4	727.7
12 MONTHS OR LONGER	873.8	321.5
TOTAL	906.2	1,049.2
U.S. Government
FAIR VALUE
LESS THAN 12 MONTHS	1,551	1,123.6
12 MONTHS OR LONGER	1,183	343.1
TOTAL	2,734	1,466.7
UNREALIZED LOSSES
LESS THAN 12 MONTHS	12.1	64.1
12 MONTHS OR LONGER	89.7	28.7
TOTAL	101.8	92.8
Obligations of States and Political Subdivisions
FAIR VALUE
LESS THAN 12 MONTHS	0	160
12 MONTHS OR LONGER	282.1	120.6
TOTAL	282.1	280.6
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0	16.8
12 MONTHS OR LONGER	19.4	13.4
TOTAL	19.4	30.2
Government Sponsored Agency
FAIR VALUE
LESS THAN 12 MONTHS	2,855	7,631.4
12 MONTHS OR LONGER	7,865.9	2,737.7
TOTAL	10,720.9	10,369.1
UNREALIZED LOSSES
LESS THAN 12 MONTHS	18.1	262.1
12 MONTHS OR LONGER	320	89.5
TOTAL	338.1	351.6
Non-U.S. Government
FAIR VALUE
LESS THAN 12 MONTHS	0	235.4
12 MONTHS OR LONGER	246.9	124.6
TOTAL	246.9	360
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0	17.3
12 MONTHS OR LONGER	24.1	10.3
TOTAL	24.1	27.6
Corporate Debt
FAIR VALUE
LESS THAN 12 MONTHS	12.4	427.3
12 MONTHS OR LONGER	229.9	130.3
TOTAL	242.3	557.6
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0.3	14.6
12 MONTHS OR LONGER	9.9	2.8
TOTAL	$ 10.2	$ 17.4
Number of debt securities, available-for-sale | Security	3	3
Debt securities, available-for-sale, continuous unrealized loss position with credit loss	$ 81.5	$ 93.8
Debt securities, available-for-sale, continuous unrealized loss position, accumulated loss, with credit loss	6.9	9.5
Net amount of recognized liabilities for repurchase agreements	0.7	1.3
Covered Bonds
FAIR VALUE
LESS THAN 12 MONTHS	0	238
12 MONTHS OR LONGER	214.8	42.8
TOTAL	214.8	280.8
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0	13.5
12 MONTHS OR LONGER	11.9	1.2
TOTAL	11.9	14.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
FAIR VALUE
LESS THAN 12 MONTHS	302.6	1,305.4
12 MONTHS OR LONGER	1,898.2	807.1
TOTAL	2,200.8	2,112.5
UNREALIZED LOSSES
LESS THAN 12 MONTHS	1.9	74.4
12 MONTHS OR LONGER	138.5	83.2
TOTAL	140.4	$ 157.6
Number of debt securities, available-for-sale | Security		1
Debt securities, available-for-sale, continuous unrealized loss position with credit loss		$ 68.3
Debt securities, available-for-sale, continuous unrealized loss position, accumulated loss, with credit loss		9.1
Other Asset-Backed
FAIR VALUE
LESS THAN 12 MONTHS	0	3,873.4
12 MONTHS OR LONGER	4,561.6	1,247.6
TOTAL	4,561.6	5,121
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0	217.5
12 MONTHS OR LONGER	195.6	70.6
TOTAL	195.6	288.1
Commercial Mortgage-Backed
FAIR VALUE
LESS THAN 12 MONTHS	0	670.9
12 MONTHS OR LONGER	856.7	215.6
TOTAL	856.7	886.5
UNREALIZED LOSSES
LESS THAN 12 MONTHS	0	47.4
12 MONTHS OR LONGER	64.7	21.8
TOTAL	$ 64.7	$ 69.2

Securities (Narrative) (Details

Securities (Narrative) (Details) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2023 USD ($)	Sep. 30, 2023 USD ($) investment	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) investment	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) investment
Debt and Equity Securities, FV-NI [Line Items]
Number of securities in an unrealized loss position | investment		1,044		1,044		1,030
Debt securities, unrealized losses		$ 906.2		$ 906.2		$ 1,049.2
Debt securities, available-for-sale, realized loss						213
Available for Sale		24,342.1		24,342.1		26,699.9
Debt securities, available-for-sale, realized gain	$ 6.9
Provision for credit losses		14.6	$ 1.4	14.1	$ 6.2
Held to maturity securities		24,920.4		24,920.4		25,036.1
Debt securities, held-to-maturity, accumulated unrecognized loss		$ 2,473.6		$ 2,473.6		$ 2,158.2
Percentage of debt securities, held-to-maturity, portfolio		1		1		1
Investment Security Gains (Losses), net		$ 0	0.3	$ (6.9)	0.3
Moodys And Standard Poors A Or Higher Rating
Debt and Equity Securities, FV-NI [Line Items]
Percentage of debt securities, held-to-maturity, portfolio		0.97		0.97		0.97
BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		$ 320.1		$ 320.1		$ 323.4
Percentage of debt securities, held-to-maturity, portfolio		0.01		0.01		0.01
NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		$ 563.6		$ 563.6		$ 502.7
Percentage of debt securities, held-to-maturity, portfolio		0.02		0.02		0.02
Government Sponsored Agency
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		$ 338.1		$ 338.1		$ 351.6
Available for Sale		11,656.8		11,656.8		11,545.2
Held to maturity securities		9,159.9		9,159.9		9,407.7
Debt securities, held-to-maturity, accumulated unrecognized loss		1,405.6		1,405.6		1,076
Government Sponsored Agency | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0		0
Government Sponsored Agency | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0		0
Obligations of States and Political Subdivisions
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		19.4		19.4		30.2
Available for Sale		282.1		282.1		787.6
Held to maturity securities		2,577.7		2,577.7		2,565.3
Debt securities, held-to-maturity, accumulated unrecognized loss		177.9		177.9		149.8
Obligations of States and Political Subdivisions | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0		0
Obligations of States and Political Subdivisions | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0		0
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		10.2		10.2		17.4
Available for Sale		380.9		380.9		1,747.6
Provision for credit losses		(0.6)	(0.9)	(0.6)	0.8
Net amount of recognized liabilities for repurchase agreements		0.7		0.7		1.3
Held to maturity securities		639.1		639.1		713.3
Debt securities, held-to-maturity, accumulated unrecognized loss		38		38		45.4
Proceeds from sale of investment securities		17.1	$ 100.2	2,200	$ 100.2
Corporate Debt | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0		0
Corporate Debt | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0		0
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		140.4		140.4		157.6
Available for Sale		2,959.8		2,959.8		2,479.4
Held to maturity securities		5,443.8		5,443.8		5,703.3
Debt securities, held-to-maturity, accumulated unrecognized loss		400.3		400.3		436.1
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		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		0
Available For Sale, Debt Securities, Portfolio For Sale
Debt and Equity Securities, FV-NI [Line Items]
Available for Sale						2,100
Commercial Mortgage-Backed
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses		64.7		64.7		69.2
Available for Sale		884.3		884.3		1,387.8
Held to maturity securities		37.6		37.6
Debt securities, held-to-maturity, accumulated unrecognized loss		0.7		0.7
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]
Debt securities, unrealized losses		195.6		195.6		288.1
Available for Sale		4,771.5		4,771.5		5,256.2
Held to maturity securities		246.6		246.6		263.7
Debt securities, held-to-maturity, accumulated unrecognized loss		0.2		0.2		1
Other Asset-Backed | BBB
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		0		0		0
Other Asset-Backed | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities		$ 0		$ 0		$ 0

Securities (Reconciliation of_2

Securities (Reconciliation of Amortized Cost to Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	$ 24,920.4	$ 25,036.1
GROSS UNREALIZED GAINS	2.9	1.4
GROSS UNREALIZED LOSSES	2,473.6	2,158.2
FAIR VALUE	22,449.7	22,879.3
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost		50
GROSS UNREALIZED GAINS		0
GROSS UNREALIZED LOSSES		0
FAIR VALUE		50
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,577.7	2,565.3
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	177.9	149.8
FAIR VALUE	2,399.8	2,415.5
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	9,159.9	9,407.7
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	1,405.6	1,076
FAIR VALUE	7,754.3	8,331.7
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	3,711.8	3,234
GROSS UNREALIZED GAINS	0.1	0.1
GROSS UNREALIZED LOSSES	126.6	133.8
FAIR VALUE	3,585.3	3,100.3
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	639.1	713.3
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	38	45.4
FAIR VALUE	601.1	667.9
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	2,116.9	2,530.3
GROSS UNREALIZED GAINS	0.4	0.3
GROSS UNREALIZED LOSSES	142	158.7
FAIR VALUE	1,975.3	2,371.9
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	405.4	35.9
GROSS UNREALIZED GAINS	0.1	0
GROSS UNREALIZED LOSSES	0	0
FAIR VALUE	405.5	35.9
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	5,443.8	5,703.3
GROSS UNREALIZED GAINS	1.3	1
GROSS UNREALIZED LOSSES	400.3	436.1
FAIR VALUE	5,044.8	5,268.2
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	246.6	263.7
GROSS UNREALIZED GAINS	1	0
GROSS UNREALIZED LOSSES	0.2	1
FAIR VALUE	247.4	262.7
Commercial Mortgage-Backed
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	37.6
GROSS UNREALIZED GAINS	0
GROSS UNREALIZED LOSSES	0.7
FAIR VALUE	36.9
Other
Schedule of Held-to-maturity Securities [Line Items]
Amortized Cost	581.6	532.6
GROSS UNREALIZED GAINS	0	0
GROSS UNREALIZED LOSSES	182.3	157.4
FAIR VALUE	$ 399.3	$ 375.2

Securities (Credit Quality Indi

Securities (Credit Quality Indicators) (Details) $ in Millions	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 24,920.4	$ 25,036.1
Percent of Total	1	1
AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 17,961.3	$ 18,179.9
Percent of Total	0.72	0.73
AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 4,089.2	$ 4,372.7
Percent of Total	0.17	0.17
A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 1,986.2	$ 1,657.4
Percent of Total	0.08	0.07
BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 320.1	$ 323.4
Percent of Total	0.01	0.01
NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	$ 563.6	$ 502.7
Percent of Total	0.02	0.02
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity		$ 50
U.S. Government | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity		50
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	$ 2,577.7	2,565.3
Obligations of States and Political Subdivisions | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	918	926.8
Obligations of States and Political Subdivisions | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	1,659.7	1,638.5
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
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	9,159.9	9,407.7
Government Sponsored Agency | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	9,159.9	9,407.7
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	3,711.8	3,234
Non-U.S. Government | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	894.1	762.2
Non-U.S. Government | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	879	926.5
Non-U.S. Government | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	1,619.7	1,223
Non-U.S. Government | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	319	322.3
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	639.1	713.3
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	299.2	305.7
Corporate Debt | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	337.7	405.5
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	2,116.9	2,530.3
Covered Bonds | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	2,116.9	2,530.3
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	405.4	35.9
Certificates of Deposit | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	367.4	0
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	38	35.9
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	5,443.8	5,703.3
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	4,162.6	4,171.3
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	1,251.3	1,502
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	28.8	28.9
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	246.6	263.7
Other Asset-Backed | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	246.6	263.7
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
Commercial Mortgage-Backed | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	37.6
Commercial Mortgage-Backed | AA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0
Commercial Mortgage-Backed | A
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0
Commercial Mortgage-Backed | BBB
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0
Commercial Mortgage-Backed | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	0
Other
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	581.6	532.6
Other | AAA
Schedule of Held-to-maturity Securities [Line Items]
Held to Maturity	56	65.8
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	$ 525.6	$ 466.8

Loans (Loans) (Details)

Loans (Loans) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 43,577	$ 42,893.3
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	21,987.3	21,635.6
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	12,061.3	12,415
Commercial | Commercial and Institutional | Private Equity Funds
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	4,800	5,600
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	5,063.1	4,773
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	2,857.8	3,131.1
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	2,005.1	1,316.5
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	21,589.7	21,257.7
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	14,068.6	14,119
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	6,285.8	6,413.5
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	432.6	510
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 802.7	$ 215.2

Loans (Narrative) (Details)

Loans (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 43,577,000,000		$ 43,577,000,000		$ 42,893,300,000
Other U.S. loans and non-U.S. loans, short duration advances	4,200,000,000		4,200,000,000		2,900,000,000
Demand deposits	4,500,000		4,500,000		24,400,000
Loan processing fee	0	$ 0	0	$ 11,200,000
Financing receivable, nonaccrual, interest income	900,000	$ 1,100,000	2,300,000	$ 3,200,000
Loans in process of foreclosure	1,100,000		1,100,000		1,100,000
Financing receivable, excluding accrued interest, modified, write-off, borrowers with financial difficulty			0
Modified loans, charged off			700,000
Nonaccrual loans, troubled debt restructurings					35,300,000
Accrual troubled debt restructurings					39,700,000
Troubled debt restructuring, commitment to lend					200,000
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, held-for-sale, not part of disposal group, after valuation allowance	0		0		0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 21,589,700,000		$ 21,589,700,000		21,257,700,000
Personal | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on Residential real estate loan, lower limit	65%		65%
Collateral required on Residential real estate loan, upper limit	80%		80%
Loans and leases	$ 6,285,800,000		$ 6,285,800,000		6,413,500,000
Personal | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products			10 years
Loans and leases	228,100,000		$ 228,100,000		$ 248,600,000
Percentage of total equity credit lines			97%		98%
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 21,987,300,000		$ 21,987,300,000		$ 21,635,600,000

Loans (Credit Quality Indicator

Loans (Credit Quality Indicator At Amortized Cost By Origination Year) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	$ 8,145.7		$ 8,145.7		$ 7,905.6
2022/2021	4,953.4		4,953.4		5,484.1
2021/2020	4,428.5		4,428.5		2,791.4
2020/2019	1,818.2		1,818.2		2,007.3
2019/2018	1,264.4		1,264.4		746.1
PRIOR	2,829.3		2,829.3		3,012.1
REVOLVING LOANS	19,428.1		19,428.1		20,561.7
REVOLVING LOANS CONVERTED TO TERM LOANS	709.4		709.4		385
TOTAL LOANS	43,577		43,577		42,893.3
2023, Charge-offs			(0.8)
2022, Charge-offs			(4.5)
2021, Charge-offs			0
2020, Charge-offs			0
2019, Charge-offs			0
Prior, Charge-offs			(0.3)
REVOLVING LOANS, Charge-offs			0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0
Charge-Offs	(0.8)	$ (5.4)	(5.6)	$ (5.5)
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	6,354		6,354		5,610.6
2022/2021	3,040.2		3,040.2		3,194.9
2021/2020	2,404		2,404		1,381.6
2020/2019	568.9		568.9		1,021.9
2019/2018	636.2		636.2		390.1
PRIOR	980.3		980.3		1,203.4
REVOLVING LOANS	7,904.1		7,904.1		8,760.2
REVOLVING LOANS CONVERTED TO TERM LOANS	99.6		99.6		72.9
TOTAL LOANS	21,987.3		21,987.3		21,635.6
2023, Charge-offs			0
2022, Charge-offs			(4.5)
2021, Charge-offs			0
2020, Charge-offs			0
2019, Charge-offs			0
Prior, Charge-offs			0
REVOLVING LOANS, Charge-offs			0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0
Charge-Offs	(0.5)	(4.9)	(4.5)	(4.9)
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	1,058.9		1,058.9		1,548.2
2022/2021	1,429.6		1,429.6		1,858.6
2021/2020	1,613.3		1,613.3		510.6
2020/2019	255.7		255.7		364.1
2019/2018	273.4		273.4		197.3
PRIOR	599.7		599.7		686
REVOLVING LOANS	6,739		6,739		7,199.6
REVOLVING LOANS CONVERTED TO TERM LOANS	91.7		91.7		50.6
TOTAL LOANS	12,061.3		12,061.3		12,415
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	355.1		355.1		753.3
2022/2021	539.8		539.8		1,087.5
2021/2020	874.3		874.3		209.8
2020/2019	95.9		95.9		159.3
2019/2018	148.3		148.3		45.9
PRIOR	417.6		417.6		511.3
REVOLVING LOANS	5,148.5		5,148.5		6,032.8
REVOLVING LOANS CONVERTED TO TERM LOANS	16		16		17.7
TOTAL LOANS	7,595.5		7,595.5		8,817.6
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	689.9		689.9		744.1
2022/2021	818.7		818.7		740.6
2021/2020	669.7		669.7		300.8
2020/2019	147.6		147.6		191.1
2019/2018	125		125		151.4
PRIOR	180.4		180.4		174.7
REVOLVING LOANS	1,549		1,549		1,102.3
REVOLVING LOANS CONVERTED TO TERM LOANS	75.3		75.3		32.9
TOTAL LOANS	4,255.6		4,255.6		3,437.9
Commercial | Commercial and Institutional | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	13.9		13.9		50.8
2022/2021	71.1		71.1		30.5
2021/2020	69.3		69.3		0
2020/2019	12.2		12.2		13.7
2019/2018	0.1		0.1		0
PRIOR	1.7		1.7		0
REVOLVING LOANS	41.5		41.5		64.5
REVOLVING LOANS CONVERTED TO TERM LOANS	0.4		0.4		0
TOTAL LOANS	210.2		210.2		159.5
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	1,711.3		1,711.3		1,294.9
2022/2021	1,595.3		1,595.3		1,290.1
2021/2020	746.8		746.8		761.4
2020/2019	247.8		247.8		619.9
2019/2018	303.9		303.9		192.8
PRIOR	197.2		197.2		296
REVOLVING LOANS	252.9		252.9		297.4
REVOLVING LOANS CONVERTED TO TERM LOANS	7.9		7.9		20.5
TOTAL LOANS	5,063.1		5,063.1		4,773
2023, Charge-offs			0
2022, Charge-offs			(4.5)
2021, Charge-offs			0
2020, Charge-offs			0
2019, Charge-offs			0
Prior, Charge-offs			0
REVOLVING LOANS, Charge-offs			0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0
Charge-Offs			(4.5)
Commercial | Commercial Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	334.2		334.2		318.7
2022/2021	331.8		331.8		227.4
2021/2020	183.5		183.5		123.6
2020/2019	19.1		19.1		123.5
2019/2018	40.8		40.8		39.8
PRIOR	45.9		45.9		39.1
REVOLVING LOANS	47.7		47.7		113.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0.5		0.5		3
TOTAL LOANS	1,003.5		1,003.5		988.5
Commercial | Commercial Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	1,360.9		1,360.9		968.5
2022/2021	1,260.2		1,260.2		1,040
2021/2020	541.7		541.7		637.8
2020/2019	228.7		228.7		447.3
2019/2018	254.9		254.9		153
PRIOR	136.7		136.7		256.9
REVOLVING LOANS	202.7		202.7		181.5
REVOLVING LOANS CONVERTED TO TERM LOANS	7.4		7.4		17.5
TOTAL LOANS	3,993.2		3,993.2		3,702.5
Commercial | Commercial Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	16.2		16.2		7.7
2022/2021	3.3		3.3		22.7
2021/2020	21.6		21.6		0
2020/2019	0		0		49.1
2019/2018	8.2		8.2		0
PRIOR	14.6		14.6		0
REVOLVING LOANS	2.5		2.5		2.5
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	66.4		66.4		82
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	1,578.7		1,578.7		1,451
2022/2021	15.3		15.3		46.2
2021/2020	43.9		43.9		109.6
2020/2019	65.4		65.4		37.9
2019/2018	58.9		58.9		0
PRIOR	183.4		183.4		221.4
REVOLVING LOANS	912.2		912.2		1,263.2
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		1.8
TOTAL LOANS	2,857.8		2,857.8		3,131.1
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	842.6		842.6		991.9
2022/2021	0		0		46.2
2021/2020	43.9		43.9		109.6
2020/2019	65.4		65.4		14.8
2019/2018	35.8		35.8		0
PRIOR	3.2		3.2		6.5
REVOLVING LOANS	823.5		823.5		1,158.3
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	1,814.4		1,814.4		2,327.3
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	689.6		689.6		459
2022/2021	0.8		0.8		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	23.1		23.1		0
PRIOR	180.2		180.2		214.9
REVOLVING LOANS	88.7		88.7		89.5
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		1.8
TOTAL LOANS	982.4		982.4		765.2
Commercial | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	46.5		46.5		0.1
2022/2021	14.5		14.5		0
2021/2020	0		0		0
2020/2019	0		0		23.1
2019/2018	0		0		0
PRIOR	0		0		0
REVOLVING LOANS	0		0		15.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	61		61		38.6
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	2,005.1		2,005.1		1,316.5
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
PRIOR	0		0		0
REVOLVING LOANS	0		0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	2,005.1		2,005.1		1,316.5
Commercial | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	1,190.9		1,190.9		993.9
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
PRIOR	0		0		0
REVOLVING LOANS	0		0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	1,190.9		1,190.9		993.9
Commercial | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	814.2		814.2		322.6
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
PRIOR	0		0		0
REVOLVING LOANS	0		0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	814.2		814.2		322.6
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	1,791.7		1,791.7		2,295
2022/2021	1,913.2		1,913.2		2,289.2
2021/2020	2,024.5		2,024.5		1,409.8
2020/2019	1,249.3		1,249.3		985.4
2019/2018	628.2		628.2		356
PRIOR	1,849		1,849		1,808.7
REVOLVING LOANS	11,524		11,524		11,801.5
REVOLVING LOANS CONVERTED TO TERM LOANS	609.8		609.8		312.1
TOTAL LOANS	21,589.7		21,589.7		21,257.7
2023, Charge-offs			(0.8)
2022, Charge-offs			0
2021, Charge-offs			0
2020, Charge-offs			0
2019, Charge-offs			0
Prior, Charge-offs			(0.3)
REVOLVING LOANS, Charge-offs			0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0
Charge-Offs	(0.3)	$ (0.5)	(1.1)	$ (0.6)
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	650.1		650.1		826.7
2022/2021	690.4		690.4		915
2021/2020	731		731		243
2020/2019	169.9		169.9		504.9
2019/2018	170.5		170.5		70.7
PRIOR	208.5		208.5		178.5
REVOLVING LOANS	10,845.9		10,845.9		11,084.8
REVOLVING LOANS CONVERTED TO TERM LOANS	602.3		602.3		295.4
TOTAL LOANS	14,068.6		14,068.6		14,119
Personal | Private Client | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	326.5		326.5		395.5
2022/2021	218.2		218.2		159.9
2021/2020	44.4		44.4		50.5
2020/2019	70		70		313.6
2019/2018	15.1		15.1		13.4
PRIOR	25		25		18.5
REVOLVING LOANS	5,723.2		5,723.2		5,352.5
REVOLVING LOANS CONVERTED TO TERM LOANS	172.8		172.8		28.2
TOTAL LOANS	6,595.2		6,595.2		6,332.1
Personal | Private Client | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	305.3		305.3		430.3
2022/2021	467.8		467.8		755.1
2021/2020	686.6		686.6		192.4
2020/2019	99.9		99.9		191.3
2019/2018	155.4		155.4		38.7
PRIOR	165.7		165.7		160
REVOLVING LOANS	5,115.6		5,115.6		5,728.6
REVOLVING LOANS CONVERTED TO TERM LOANS	429.5		429.5		267.2
TOTAL LOANS	7,425.8		7,425.8		7,763.6
Personal | Private Client | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	18.3		18.3		0.9
2022/2021	4.4		4.4		0
2021/2020	0		0		0.1
2020/2019	0		0		0
2019/2018	0		0		18.6
PRIOR	17.8		17.8		0
REVOLVING LOANS	7.1		7.1		3.7
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	47.6		47.6		23.3
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	313.8		313.8		1,225.9
2022/2021	1,198.4		1,198.4		1,330.2
2021/2020	1,253.5		1,253.5		1,166.8
2020/2019	1,079.4		1,079.4		459.2
2019/2018	438.9		438.9		277.5
PRIOR	1,626.7		1,626.7		1,624.9
REVOLVING LOANS	375.1		375.1		320.1
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		8.9
TOTAL LOANS	6,285.8		6,285.8		6,413.5
2023, Charge-offs			(0.8)
2022, Charge-offs			0
2021, Charge-offs			0
2020, Charge-offs			0
2019, Charge-offs			0
Prior, Charge-offs			(0.3)
REVOLVING LOANS, Charge-offs			0
REVOLVING LOANS CONVERTED TO TERM LOANS, Charge-offs			0
Charge-Offs			(1.1)
Personal | Residential Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	198.7		198.7		871.6
2022/2021	536.2		536.2		666.7
2021/2020	565.4		565.4		567.7
2020/2019	405.1		405.1		168.1
2019/2018	154.2		154.2		102.9
PRIOR	729.2		729.2		750.8
REVOLVING LOANS	229.2		229.2		128.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		7.9
TOTAL LOANS	2,818		2,818		3,264.1
Personal | Residential Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	115.1		115.1		354.3
2022/2021	644.7		644.7		656.7
2021/2020	682.6		682.6		597.6
2020/2019	672.1		672.1		290
2019/2018	273.7		273.7		170.9
PRIOR	863.7		863.7		838.2
REVOLVING LOANS	142.9		142.9		180.4
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		1
TOTAL LOANS	3,394.8		3,394.8		3,089.1
Personal | Residential Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	0		0		0
2022/2021	17.5		17.5		6.8
2021/2020	5.5		5.5		1.5
2020/2019	2.2		2.2		1.1
2019/2018	11		11		3.7
PRIOR	33.8		33.8		35.9
REVOLVING LOANS	3		3		11.3
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	73		73		60.3
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	25.1		25.1		27.2
2022/2021	24.4		24.4		44
2021/2020	40		40		0
2020/2019	0		0		21.3
2019/2018	18.8		18.8		7.8
PRIOR	13.8		13.8		5.3
REVOLVING LOANS	303		303		396.6
REVOLVING LOANS CONVERTED TO TERM LOANS	7.5		7.5		7.8
TOTAL LOANS	432.6		432.6		510
Personal | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	16.1		16.1		3
2022/2021	3.7		3.7		3.7
2021/2020	0.6		0.6		0
2020/2019	0		0		0
2019/2018	0		0		4.6
PRIOR	5.5		5.5		2.3
REVOLVING LOANS	54		54		124.6
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	79.9		79.9		138.2
Personal | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	9		9		24.2
2022/2021	20.7		20.7		40.3
2021/2020	39.4		39.4		0
2020/2019	0		0		21.3
2019/2018	18.8		18.8		3.2
PRIOR	8.3		8.3		2.9
REVOLVING LOANS	249		249		272
REVOLVING LOANS CONVERTED TO TERM LOANS	7.5		7.5		7.8
TOTAL LOANS	352.7		352.7		371.7
Personal | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022					0
2022/2021					0
2021/2020					0
2020/2019					0
2019/2018					0
PRIOR					0.1
REVOLVING LOANS					0
REVOLVING LOANS CONVERTED TO TERM LOANS					0
TOTAL LOANS					0.1
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	802.7		802.7		215.2
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
PRIOR	0		0		0
REVOLVING LOANS	0		0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	802.7		802.7		215.2
Personal | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	90.5		90.5		190.8
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
PRIOR	0		0		0
REVOLVING LOANS	0		0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	90.5		90.5		190.8
Personal | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2023/2022	712.2		712.2		24.4
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
PRIOR	0		0		0
REVOLVING LOANS	0		0		0
REVOLVING LOANS CONVERTED TO TERM LOANS	0		0		0
TOTAL LOANS	$ 712.2		$ 712.2		$ 24.4

Loans (Delinquency Status) (Det

Loans (Delinquency Status) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	$ 43,508.2	$ 42,847.4
NONACCRUAL	68.8	45.9
TOTAL LOANS	43,577	42,893.3
NONACCRUAL WITH NO ALLOWANCE	56	28.9
Other Real Estate Owned	0.3	0
Total Nonaccrual Assets	69.1	45.9
CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	43,353.7	42,504.6
30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	101.9	243.4
60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	16.4	45.2
90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	36.2	54.2
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,967.8	21,608
NONACCRUAL	19.5	27.6
TOTAL LOANS	21,987.3	21,635.6
NONACCRUAL WITH NO ALLOWANCE	10.1	10.6
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	12,045	12,397.6
NONACCRUAL	16.3	17.4
TOTAL LOANS	12,061.3	12,415
NONACCRUAL WITH NO ALLOWANCE	6.9	4.4
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,059.9	4,762.8
NONACCRUAL	3.2	10.2
TOTAL LOANS	5,063.1	4,773
NONACCRUAL WITH NO ALLOWANCE	3.2	6.2
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,857.8	3,131.1
NONACCRUAL	0	0
TOTAL LOANS	2,857.8	3,131.1
NONACCRUAL WITH NO ALLOWANCE	0	0
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,005.1	1,316.5
NONACCRUAL	0	0
TOTAL LOANS	2,005.1	1,316.5
NONACCRUAL WITH NO ALLOWANCE	0	0
Commercial | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,952.2	21,562.8
Commercial | CURRENT | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	12,032.4	12,353.7
Commercial | CURRENT | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,059.9	4,761.5
Commercial | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,854.8	3,131.1
Commercial | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,005.1	1,316.5
Commercial | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	10.9	41.5
Commercial | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	7.9	40.2
Commercial | 30 – 59 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	1.3
Commercial | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3	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	1.6	3
Commercial | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	1.6	3
Commercial | 60 – 89 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
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	3.1	0.7
Commercial | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3.1	0.7
Commercial | 90 DAYS OR MORE PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	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	21,540.4	21,239.4
NONACCRUAL	49.3	18.3
TOTAL LOANS	21,589.7	21,257.7
NONACCRUAL WITH NO ALLOWANCE	45.9	18.3
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	14,048.8	14,119
NONACCRUAL	19.8	0
TOTAL LOANS	14,068.6	14,119
NONACCRUAL WITH NO ALLOWANCE	17.8	0
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,256.3	6,395.2
NONACCRUAL	29.5	18.3
TOTAL LOANS	6,285.8	6,413.5
NONACCRUAL WITH NO ALLOWANCE	28.1	18.3
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	432.6	510
NONACCRUAL	0	0
TOTAL LOANS	432.6	510
NONACCRUAL WITH NO ALLOWANCE	0	0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	802.7	215.2
NONACCRUAL	0	0
TOTAL LOANS	802.7	215.2
NONACCRUAL WITH NO ALLOWANCE	0	0
Personal | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,401.5	20,941.8
Personal | CURRENT | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	13,911.3	13,843.5
Personal | CURRENT | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,254.9	6,373.2
Personal | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	432.6	509.9
Personal | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	802.7	215.2
Personal | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	91	201.9
Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	91	192.3
Personal | 30 – 59 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	9.6
Personal | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	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	14.8	42.2
Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	13.4	29.9
Personal | 60 – 89 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	1.4	12.3
Personal | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0
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	33.1	53.5
Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	33.1	53.3
Personal | 90 DAYS OR MORE PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0.1
Personal | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0	0.1
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 ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 21,500,000	$ 24,600,000
% OF TOTAL SEGMENT	0.05%	0.06%
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 16,700,000	$ 16,700,000
% OF TOTAL SEGMENT	0.08%	0.08%
Commercial | Commercial and Institutional | Extension of term
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 16,700,000	$ 16,700,000
% OF TOTAL SEGMENT	0.14%	0.14%
Financing receivable, modified, weighted average term increase from modification	12 months	12 months
Commercial | Commercial Real Estate | Combination of principal and/or interest deferral and extension of term
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 0	$ 0
% OF TOTAL SEGMENT	0%	0%
Commercial | Commercial Real Estate | Principal and/or interest deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, excluding accrued interest, modified, deferred interest and principal		$ 32,500,000
Financing receivable, modified, weighted average term increase from modification		6 months
Commercial | Commercial Real Estate | Extension of term
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, weighted average term increase from modification		6 months
Personal
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 4,800,000	$ 7,900,000
% OF TOTAL SEGMENT	0.02%	0.04%
Financing receivable, excluding accrued interest, modified in period, loans with no outstanding balance, amount		$ 0
Personal | Commercial Real Estate | Combination of principal and/or interest deferral and extension of term
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, excluding accrued interest, modified, deferred interest and principal		32,500,000
Personal | Residential Real Estate | Combination of principal and/or interest deferral and extension of term
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 4,700,000	$ 4,700,000
% OF TOTAL SEGMENT	0.08%	0.08%
Personal | Residential Real Estate | Principal and/or interest deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 100,000	$ 3,200,000
% OF TOTAL SEGMENT	0%	0.05%
Financing receivable, modified, weighted average term increase from modification	9 months	9 months
Personal | Residential Real Estate | Extension of term
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, weighted average term increase from modification	9 months	9 months
Personal | Private Client | Extension of term
Financing Receivable, Troubled Debt Restructuring [Line Items]
AMORTIZED COST BASIS	$ 0	$ 0
% OF TOTAL SEGMENT	0%	0%
Financing receivable, excluding accrued interest, modified, deferred interest and principal		$ 200,000
Financing receivable, modified, weighted average term increase from modification		60 months

Loans (Troubled Debt Restructur

Loans (Troubled Debt Restructurings) (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2022 USD ($) contract	Sep. 30, 2022 USD ($) contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	3	6
RECORDED INVESTMENT	$ 31.8	$ 32.4
UNPAID PRINCIPAL BALANCE	$ 32.7	$ 33.3
COMMERCIAL
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	2	3
RECORDED INVESTMENT	$ 31.7	$ 32.2
UNPAID PRINCIPAL BALANCE	$ 32.6	$ 33.1
COMMERCIAL | Commercial and Institutional
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	1	2
RECORDED INVESTMENT	$ 0.1	$ 0.6
UNPAID PRINCIPAL BALANCE	$ 0.1	$ 0.6
COMMERCIAL | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	1	1
RECORDED INVESTMENT	$ 31.6	$ 31.6
UNPAID PRINCIPAL BALANCE	$ 32.5	$ 32.5
Personal
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	1	3
RECORDED INVESTMENT	$ 0.1	$ 0.2
UNPAID PRINCIPAL BALANCE	$ 0.1	$ 0.2
Personal | Residential Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	1	3
RECORDED INVESTMENT	$ 0.1	$ 0.2
UNPAID PRINCIPAL BALANCE	$ 0.1	$ 0.2

Allowance for Credit Losses (Ch

Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
LOANS
Balance at Beginning of Period	$ 152.5	$ 138.2	$ 144.3	$ 138.4
Charge-Offs	(0.8)	(5.4)	(5.6)	(5.5)
Recoveries	1.1	0.9	3	9.7
Net Recoveries (Charge-Offs)	0.3	(4.5)	(2.6)	4.2
Provision for (Release of) Credit Losses	14	5	25.1	(3.9)
Balance at End of Period	166.8	138.7	166.8	138.7
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	26	43.5	38.5	34.1
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net Recoveries (Charge-Offs)	0	0	0	0
Provision for (Release of) Credit Losses	2.3	(2.8)	(10.2)	6.6
Balance at End of Period	28.3	40.7	28.3	40.7
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	16.7	15.4	16	11.2
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net Recoveries (Charge-Offs)	0	0	0	0
Provision for (Release of) Credit Losses	(1.8)	(0.4)	(1.1)	3.8
Balance at End of Period	14.9	15	14.9	15
OTHER FINANCIAL ASSETS
Balance at Beginning of Period	1	1.1	0.8	1
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net Recoveries (Charge-Offs)	0	0	0	0
Provision for (Release of) Credit Losses(1)	0.1	(0.4)	0.3	(0.3)
Balance at End of Period	1.1	0.7	1.1	0.7
TOTAL
Balance at Beginning of Period	196.2	198.2	199.6	184.7
Charge-Offs	(0.8)	(5.4)	(5.6)	(5.5)
Recoveries	1.1	0.9	3	9.7
Net Recoveries (Charge-Offs)	0.3	(4.5)	(2.6)	4.2
Provision for (release of) credit losses	14.6	1.4	14.1	6.2
Balance at End of Period	211.1	195.1	211.1	195.1
Corporate Debt
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	1.4	1.8	1.9	1.4
Provision for (Release of) Credit Losses	(0.1)	(0.3)	(0.6)	0.1
Balance at End of Period	1.3	1.5	1.3	1.5
TOTAL
Provision for (release of) credit losses	$ (0.6)	$ (0.9)	$ (0.6)	$ 0.8

Allowance for Credit Losses (Na

Allowance for Credit Losses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022	Dec. 31, 2021
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Provision for (release of) credit losses	$ 14.6	$ 1.4	$ 14.1	$ 6.2
Net recoveries (charge-offs)	(0.3)	4.5	$ 2.6	(4.2)
Time period used for projecting future conditions to estimate credit losses			2 years
Other financial assets, allowance for credit loss	1.1	0.7	$ 1.1	0.7	$ 1	$ 0.8	$ 1.1	$ 1
Corporate Debt
Debt Securities, Held-to-maturity, Allowance for Credit Loss [Line Items]
Provision for (release of) credit losses	$ (0.6)	$ (0.9)	$ (0.6)	$ 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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
LOANS
Balance at Beginning of Period	$ 152.5	$ 138.2	$ 144.3	$ 138.4
Balance at End of Period	166.8	138.7	166.8	138.7
Charge-Offs	0.8	5.4	5.6	5.5
Recoveries	1.1	0.9	3	9.7
Net Recoveries (Charge-Offs)	0.3	(4.5)	(2.6)	4.2
Provision for (Release of) Credit Losses	14	5	25.1	(3.9)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	26	43.5	38.5	34.1
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net Recoveries (Charge-Offs)	0	0	0	0
Provision for (Release of) Credit Losses	2.3	(2.8)	(10.2)	6.6
Balance at End of Period	28.3	40.7	28.3	40.7
COMMERCIAL
LOANS
Balance at Beginning of Period	124	102.5	116.2	105.6
Balance at End of Period	137.4	100.6	137.4	100.6
Charge-Offs	0.5	4.9	4.5	4.9
Recoveries	0	0.3	0.1	2.7
Net Recoveries (Charge-Offs)	(0.5)	(4.6)	(4.4)	(2.2)
Provision for (Release of) Credit Losses	13.9	2.7	25.6	(2.8)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	23.3	40.3	36.3	31.4
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net Recoveries (Charge-Offs)	0	0	0	0
Provision for (Release of) Credit Losses	2.2	(2.8)	(10.8)	6.1
Balance at End of Period	25.5	37.5	25.5	37.5
PERSONAL
LOANS
Balance at Beginning of Period	28.5	35.7	28.1	32.8
Balance at End of Period	29.4	38.1	29.4	38.1
Charge-Offs	0.3	0.5	1.1	0.6
Recoveries	1.1	0.6	2.9	7
Net Recoveries (Charge-Offs)	0.8	0.1	1.8	6.4
Provision for (Release of) Credit Losses	0.1	2.3	(0.5)	(1.1)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	2.7	3.2	2.2	2.7
Charge-Offs	0	0	0	0
Recoveries	0	0	0	0
Net Recoveries (Charge-Offs)	0	0	0	0
Provision for (Release of) Credit Losses	0.1	0	0.6	0.5
Balance at End of Period	$ 2.8	$ 3.2	$ 2.8	$ 3.2

Allowance for Credit Losses (Re

Allowance for Credit Losses (Recorded Investments in Loans) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Loans
Evaluated on an Individual Basis	$ 94.7		$ 109.1
Evaluated on a Collective Basis	43,482.3		42,784.2
TOTAL LOANS	43,577		42,893.3
Allowance for Credit Losses on Loans
Evaluated on an Individual Basis	10.3		10.4
Evaluated on a Collective Basis	156.5		133.9
Allowance Assigned to Loans	166.8	$ 152.5	144.3	$ 138.7	$ 138.2	$ 138.4
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0		0
Evaluated on a Collective Basis	28.3		38.5
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	28.3	26	38.5	40.7	43.5	34.1
Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit	195.1		182.8
COMMERCIAL
Loans
Evaluated on an Individual Basis	27.4		63
Evaluated on a Collective Basis	21,959.9		21,572.6
TOTAL LOANS	21,987.3		21,635.6
Allowance for Credit Losses on Loans
Evaluated on an Individual Basis	8.3		10.4
Evaluated on a Collective Basis	129.1		105.8
Allowance Assigned to Loans	137.4	124	116.2	100.6	102.5	105.6
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0		0
Evaluated on a Collective Basis	25.5		36.3
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	25.5	23.3	36.3	37.5	40.3	31.4
Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit	162.9		152.5
PERSONAL
Loans
Evaluated on an Individual Basis	67.3		46.1
Evaluated on a Collective Basis	21,522.4		21,211.6
TOTAL LOANS	21,589.7		21,257.7
Allowance for Credit Losses on Loans
Evaluated on an Individual Basis	2		0
Evaluated on a Collective Basis	27.4		28.1
Allowance Assigned to Loans	29.4	28.5	28.1	38.1	35.7	32.8
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0		0
Evaluated on a Collective Basis	2.8		2.2
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	2.8	$ 2.7	2.2	$ 3.2	$ 3.2	$ 2.7
Total Allowance Assigned to Loans and Undrawn Loan Commitments and Standby Letters of Credit	$ 32.2		$ 30.3

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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	$ 16.7	$ 15.4	$ 16	$ 11.2
Provision for (Release of) Credit Losses	(1.8)	(0.4)	(1.1)	3.8
Balance at End of Period	14.9	15	14.9	15
CORPORATE DEBT
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	1.4	1.8	1.9	1.4
Provision for (Release of) Credit Losses	(0.1)	(0.3)	(0.6)	0.1
Balance at End of Period	1.3	1.5	1.3	1.5
NON-U.S. GOVERNMENT
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	5.4	3.8	3.6	1.9
Provision for (Release of) Credit Losses	(0.8)	(0.7)	1	1.2
Balance at End of Period	4.6	3.1	4.6	3.1
SUB-SOVEREIGN, SUPRANATIONAL, AND NON-U.S. AGENCY BONDS
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	3.4	4.8	4	3
Provision for (Release of) Credit Losses	(0.5)	(1)	(1.1)	0.8
Balance at End of Period	2.9	3.8	2.9	3.8
OBLIGATIONS OF STATES AND POICITAL SUBDIVISIONS
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	1.3	0	1.5	0
Provision for (Release of) Credit Losses	(0.1)	0	(0.3)	0
Balance at End of Period	1.2	0	1.2	0
COVERED BONDS
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	0.1	0.1	0.1	0.1
Provision for (Release of) Credit Losses	0	0	0	0
Balance at End of Period	0.1	0.1	0.1	0.1
OTHER
HELD TO MATURITY DEBT SECURITIES
Balance at Beginning of Period	5.1	4.9	4.9	4.8
Provision for (Release of) Credit Losses	(0.3)	1.6	(0.1)	1.7
Balance at End of Period	$ 4.8	$ 6.5	$ 4.8	$ 6.5

Allowance for Credit Losses (Ac

Allowance for Credit Losses (Accrued Interest) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Receivables [Abstract]
Loans	$ 249.4	$ 203.1
Debt Securities
Held to Maturity	82.7	63.2
Available for Sale	138	147.1
Other Financial Assets	58.4	43.8
Total	$ 528.5	$ 457.2

Pledged Assets, Collateral an_3

Pledged Assets, Collateral and Restricted Assets (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Financial Instruments Owned and Pledged as Collateral [Line Items]
Cash, held in foreign currency	$ 642,800,000		$ 642,800,000		$ 330,400,000
Restricted cash	553,600,000		553,600,000		574,200,000
Average deposits maintained to meet Federal Reserve Bank reserve requirements	0	$ 0	0	$ 0
Collateral that may be repledged or sold
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned at fair value	39,000,000,000		39,000,000,000		43,200,000,000
Asset Pledged as Collateral with Right
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned at fair value	540,700,000		540,700,000		464,700,000
Collateral Requirements | Collateral that may be repledged or sold
Financial Instruments Owned and Pledged as Collateral [Line Items]
Financial instruments owned at fair value	$ 13,100,000,000		$ 13,100,000,000		$ 8,700,000,000

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	Sep. 30, 2023	Dec. 31, 2022
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 39	$ 43.2
SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	27.8	31.4
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 11.2	$ 11.8

Pledged Assets, Collateral an_5

Pledged Assets, Collateral and Restricted Assets (Fair Value Of Available For Sale Debt Securities Included In Pledged Assets) (Details) - Collateral that may be repledged or sold - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financial Instruments Owned and Pledged as Collateral [Line Items]
Debt securities available for sale	$ 39,000	$ 43,200
SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE
Financial Instruments Owned and Pledged as Collateral [Line Items]
Debt securities available for sale	540.7	464.7
DERIVATIVE CONTRACTS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Debt securities available for sale	$ 15.6	$ 34.7

Pledged Assets, Collateral an_6

Pledged Assets, Collateral and Restricted Assets (Accepted Collateral) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Collateral Accepted	$ 49,987	$ 12,574.4
Fair value of securities received as collateral that have been resold or repledged	49,600	11,500
Reverse repurchase agreements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	49,972.7	12,119.4
Reverse repurchase agreements	0	450
DERIVATIVE CONTRACTS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 14.3	$ 5

Goodwill and Other Intangible_2

Goodwill and Other Intangibles (Goodwill by Reporting Segment) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2023 USD ($)
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 691.3
Foreign Exchange Rates	1.5
Goodwill, Ending Balance	692.8
ASSET SERVICING
Goodwill [Roll Forward]
Goodwill, Beginning Balance	611
Foreign Exchange Rates	1.5
Goodwill, Ending Balance	612.5
WEALTH MANAGEMENT
Goodwill [Roll Forward]
Goodwill, Beginning Balance	80.3
Foreign Exchange Rates	0
Goodwill, Ending Balance	$ 80.3

Goodwill and Other Intangible_3

Goodwill and Other Intangibles (Other Intangible Assets and Capitalized Software) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 128.7	$ 197.9
Less: Accumulated Amortization	58.4	120.3
Net Book Value	70.3	77.6
Computer Software
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	3,896.1	3,479.3
Less: Accumulated Amortization	1,881.6	1,517.4
Net Book Value	$ 2,014.5	$ 1,961.9

Goodwill and Other Intangible_4

Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets amortization	$ 2.3	$ 2.2	$ 7	$ 7.1
Estimated future amortization expense for 2022	2.3		2.3
Estimated future amortization expense for 2023	9		9
Estimated future amortization expense for 2024	8.5		8.5
Estimated future amortization expense for 2025	8.1		8.1
Estimated future amortization expense for 2026	7.9		7.9
Computer Software
Acquired Finite-Lived Intangible Assets [Line Items]
Other intangible assets amortization	$ 126.7	$ 111.1	$ 370.8	$ 317

Reporting Segments (Results of

Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)	Mar. 31, 2022 USD ($)	Sep. 30, 2023 USD ($) segment	Sep. 30, 2022 USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment							2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,111.9			$ 1,078.7			$ 3,271.8	$ 3,390.5
Foreign Exchange Trading Income	51.8			64.7			154.9	223.2
Other Noninterest Income (Loss)	106.6			98.4			302.6	275.8
Total Noninterest Income	1,270.3			1,241.8			3,729.3	3,889.5
Net Interest Income	456.2			513			1,498.9	1,352.7
Revenue	1,726.5			1,754.8			5,228.2	5,242.2
Provision for Credit Losses	14			0.5			13.5	7
Noninterest Expense	1,278.2			1,229.8			3,895.7	3,659.3
Income before Income Taxes	434.3			524.5			1,319	1,575.9
Provision for Income Taxes	106.5			129.7			324.8	395.6
Net Income	$ 327.8	$ 331.8	$ 334.6	$ 394.8	$ 396.2	$ 389.3	$ 994.2	$ 1,180.3
Percentage of Consolidated Net Income	100%			100%			100%	100%
Average Assets	$ 140,201.6			$ 146,402.2			$ 144,691.6	$ 154,152.1
RECONCILING ITEMS
Noninterest Income
Trust, Investment and Other Servicing Fees	0			0			0	0
Foreign Exchange Trading Income	0			0			0	0
Other Noninterest Income (Loss)	0			0			0	0
Total Noninterest Income	0			0			0	0
Net Interest Income	(13.2)			(12.3)			(39.5)	(30.1)
Revenue	(13.2)			(12.3)			(39.5)	(30.1)
Provision for Credit Losses	0			0			0	0
Noninterest Expense	0			0			0	0
Income before Income Taxes	(13.2)			(12.3)			(39.5)	(30.1)
Provision for Income Taxes	(13.2)			(12.3)			(39.5)	(30.1)
Net Income	0			0			0	0
OTHER
Noninterest Income
Trust, Investment and Other Servicing Fees	0			0			0	0
Foreign Exchange Trading Income	0			0			0	0
Other Noninterest Income (Loss)	2.4			(1.1)			(9.2)	(11.2)
Total Noninterest Income	2.4			(1.1)			(9.2)	(11.2)
Net Interest Income	0			0			0	0
Revenue	2.4			(1.1)			(9.2)	(11.2)
Provision for Credit Losses	0			0			0	0
Noninterest Expense	12			20.4			33.6	56.7
Income before Income Taxes	(9.6)			(21.5)			(42.8)	(67.9)
Provision for Income Taxes	(2.3)			(5.3)			(10.6)	(16.9)
Net Income	$ (7.3)			$ (16.2)			$ (32.2)	$ (51)
Percentage of Consolidated Net Income	(2.00%)			(4.00%)			(3.00%)	(4.00%)
Average Assets	$ 0			$ 0			$ 0	$ 0
ASSET SERVICING | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	626			603.2			1,850.2	1,908.4
Foreign Exchange Trading Income	54.3			63.7			161.2	215.9
Other Noninterest Income (Loss)	66.1			62.5			199	185.4
Total Noninterest Income	746.4			729.4			2,210.4	2,309.7
Net Interest Income	281.2			303.3			902.6	748.5
Revenue	1,027.6			1,032.7			3,113	3,058.2
Provision for Credit Losses	3.1			(5.1)			(3.3)	3.8
Noninterest Expense	809.3			760.4			2,459.7	2,269.4
Income before Income Taxes	215.2			277.4			656.6	785
Provision for Income Taxes	54.3			67.7			167.4	194
Net Income	$ 160.9			$ 209.7			$ 489.2	$ 591
Percentage of Consolidated Net Income	49%			53%			49%	50%
Average Assets	$ 108,656.7			$ 109,677.2			$ 110,380.4	$ 117,251
WEALTH MANAGEMENT | Operating Segments
Noninterest Income
Trust, Investment and Other Servicing Fees	485.9			475.5			1,421.6	1,482.1
Foreign Exchange Trading Income	(2.5)			1			(6.3)	7.3
Other Noninterest Income (Loss)	38.1			37			112.8	101.6
Total Noninterest Income	521.5			513.5			1,528.1	1,591
Net Interest Income	188.2			222			635.8	634.3
Revenue	709.7			735.5			2,163.9	2,225.3
Provision for Credit Losses	10.9			5.6			16.8	3.2
Noninterest Expense	456.9			449			1,402.4	1,333.2
Income before Income Taxes	241.9			280.9			744.7	888.9
Provision for Income Taxes	67.7			79.6			207.5	248.6
Net Income	$ 174.2			$ 201.3			$ 537.2	$ 640.3
Percentage of Consolidated Net Income	53%			51%			54%	54%
Average Assets	$ 31,544.9			$ 36,725			$ 34,311.2	$ 36,901.1

Stockholders' Equity (Narrative

Stockholders' Equity (Narrative) (Details) - USD ($)			3 Months Ended						9 Months Ended
	Jul. 18, 2023	Apr. 26, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022	Dec. 31, 2021	Oct. 31, 2021
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)			10,000,000						10,000,000		10,000,000
Stockholders' equity			$ 11,847,200,000	$ 11,635,700,000	$ 11,587,800,000	$ 11,030,400,000	$ 11,069,700,000	$ 11,409,800,000	$ 11,847,200,000	$ 11,030,400,000	$ 11,259,500,000	$ 12,016,800,000
Common stock dividends (in usd per share)			$ 0.75	$ 0.75	$ 0.75	$ 0.75	$ 0.70	$ 0.70
Stock repurchase program, number of shares authorized to be repurchased (in shares)													25,000,000
Stock repurchase, shares (in shares)			14,738			11,080			2,426,793	309,334
Stock repurchase, aggregate cost			$ 1,100,000	$ 99,300,000	$ 100,900,000	$ 1,200,000	$ 300,000	$ 33,800,000	$ 201,300,000	$ 35,200,000
Share-based payment arrangement, shares withheld for tax withholding obligation (in shares)									356,145
Average price paid per share for common stock repurchased (in usd per share)			$ 77.39			$ 96.43			$ 82.95	$ 113.89
Preferred Stock
Class of Stock [Line Items]
Stockholders' equity			$ 884,900,000	$ 884,900,000	$ 884,900,000	$ 884,900,000	$ 884,900,000	$ 884,900,000	$ 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		5,000
Preferred stock, without par value (in dollars per share)			$ 0						$ 0
Preferred stock, liquidation preference			$ 100,000						$ 100,000
Depository shares, liquidation preference per share (in dollars per share)			$ 1,000						$ 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		$ 493,500,000
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)			16,000						16,000		16,000
Percentage of ownership interest per each depository shares			0.10%						0.10%
Preferred stock, without par value (in dollars per share)			$ 0						$ 0
Preferred stock, liquidation preference			$ 25,000						$ 25,000
Depository shares, liquidation preference per share (in dollars per share)			$ 25						$ 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		$ 391,400,000
Series D Preferred Stock, Depositary Shares
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)			500,000						500,000
Preferred stock, shares issued (in shares)			500,000						500,000
Percentage of ownership interest per each depository shares			1%						1%
Series E Preferred Stock Depositary Shares
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)			16,000,000						16,000,000
Preferred stock, shares issued (in shares)			16,000,000						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						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 11,635.7	$ 11,587.8	$ 11,259.5	$ 11,069.7	$ 11,409.8	$ 12,016.8	$ 11,259.5	$ 12,016.8
Net Change	42.5	(39.7)	203	(274.4)	(603.6)	(871.4)	205.8	(1,749.4)
Ending balance	11,847.2	11,635.7	11,587.8	11,030.4	11,069.7	11,409.8	11,847.2	11,030.4
TOTAL
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(1,405.9)	(1,366.2)	(1,569.2)	(1,510.6)	(907)	(35.6)	(1,569.2)	(35.6)
Net Change	42.5	(39.7)	203	(274.4)	(603.6)	(871.4)
Ending balance	(1,363.4)	(1,405.9)	(1,366.2)	(1,785)	(1,510.6)	(907)	(1,363.4)	(1,785)
NET UNREALIZED GAINS (LOSSES) ON AVAILABLE FOR SALE DEBT SECURITIES
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(1,229.4)		(1,367.6)	(1,294.7)		107.1	(1,367.6)	107.1
Net Change	32.3			(272.2)			170.5	(1,674)
Ending balance	(1,197.1)	(1,229.4)		(1,566.9)	(1,294.7)		(1,197.1)	(1,566.9)
NET UNREALIZED GAINS (LOSSES) ON CASH FLOW HEDGES
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	0.5		1.2	0.6		(2.4)	1.2	(2.4)
Net Change	(0.4)			2.1			(1.1)	5.1
Ending balance	0.1	0.5		2.7	0.6		0.1	2.7
NET FOREIGN CURRENCY ADJUSTMENT
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	189.2		164.6	137.6		155.2	164.6	155.2
Net Change	9.6			20.2			34.2	2.6
Ending balance	198.8	189.2		157.8	137.6		198.8	157.8
NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(366.2)		$ (367.4)	(354.1)		$ (295.5)	(367.4)	(295.5)
Net Change	1			(24.5)			2.2	(83.1)
Ending balance	$ (365.2)	$ (366.2)		$ (378.6)	$ (354.1)		$ (365.2)	$ (378.6)

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						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
PRE-TAX
Net Change	$ 86			$ (316.1)			$ 281.8	$ (2,230.1)
TAX
Net Change	(43.5)			41.7			(76)	480.7
AFTER TAX
Net Change	42.5	$ (39.7)	$ 203	(274.4)	$ (603.6)	$ (871.4)	205.8	(1,749.4)
Unrealized Gains (Losses) on Available for Sale Debt Securities
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	18			(385.6)			158.6	(2,288.3)
Net Change	44.7			(364.3)			230.7	(2,252.3)
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(5.6)			97.5			(42)	587.4
Net Change	(12.4)			92.1			(60.2)	578.3
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	12.4			(288.1)			116.6	(1,700.9)
Net Change	32.3			(272.2)			170.5	(1,674)
Interest Income on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	26.7			21			79	35.7
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(6.8)			(5.3)			(19.9)	(9)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	19.9			15.7			59.1	26.7
Net Losses on Debt Securities
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0			0.3			(6.9)	0.3
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0			(0.1)			1.7	(0.1)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0			0.2			(5.2)	0.2
Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(14.9)			0.6			(17.7)	3.8
Net Change	(0.6)			2.8			(1.5)	6.8
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	3.8			(0.1)			4.5	(0.9)
Net Change	0.2			(0.7)			0.4	(1.7)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(11.1)			0.5			(13.2)	2.9
Net Change	(0.4)			2.1			(1.1)	5.1
Foreign Currency Adjustments
PRE-TAX
Net Change	40.5			78.3			49.3	126.2
TAX
Net Change	(30.9)			(58.1)			(15.1)	(123.6)
AFTER TAX
Net Change	9.6			20.2			34.2	2.6
Foreign Currency Translation Adjustments
PRE-TAX
Net Change	(89.2)			(168.1)			(15.7)	(382.1)
TAX
Net Change	1.7			3.9			1.2	4.5
AFTER TAX
Net Change	(87.5)			(164.2)			(14.5)	(377.6)
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
PRE-TAX
Net Change	(0.2)			(2)			(1.8)	(3.8)
TAX
Net Change	0.1			0.5			0.5	1
AFTER TAX
Net Change	(0.1)			(1.5)			(1.3)	(2.8)
Net Investment Hedge Gains (Losses)
PRE-TAX
Net Change	129.9			248.4			66.8	512.1
TAX
Net Change	(32.7)			(62.5)			(16.8)	(129.1)
AFTER TAX
Net Change	97.2			185.9			50	383
Pension and Other Postretirement Benefit Adjustments
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(0.2)			(51.6)			(1.5)	(165.2)
Net Change	1.4			(32.9)			3.3	(110.8)
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	0			13			0.1	41.2
Net Change	(0.4)			8.4			(1.1)	27.7
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(0.2)			(38.6)			(1.4)	(124)
Net Change	1			(24.5)			2.2	(83.1)
Amortization of Net Actuarial Loss
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	1.6			1.9			4.8	17.1
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.4)			(0.4)			(1.2)	(4.2)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	1.2			1.5			3.6	12.9
Amortization of Prior Service Cost (Credit)
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0			(0.2)			0	(0.7)
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0			0.1			0	0.2
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0			(0.1)			0	(0.5)
Settlement Loss
PRE-TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0			17			0	38
TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0			(4.3)			0	(9.5)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	0			12.7			0	28.5
Foreign Exchange Contracts | Unrealized Gains (Losses) on Cash Flow Hedges
PRE-TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	14.3			2.2			16.2	3
TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	(3.6)			(0.6)			(4.1)	(0.8)
AFTER TAX
Unrealized Gains (Losses) on Available for Sale Debt Securities	$ 10.7			$ 1.6			$ 12.1	$ 2.2

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						9 Months Ended
	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Basic Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	207,021,554			208,400,135			207,611,420	208,271,070
Net Income	$ 327.8	$ 331.8	$ 334.6	$ 394.8	$ 396.2	$ 389.3	$ 994.2	$ 1,180.3
Less: Dividends on Preferred Stock	16.2			16.2			37.1	37.1
Net Income Applicable to Common Stock	311.6			378.6			957.1	1,143.2
Less: Earnings Allocated to Participating Securities	3.1			3.2			9.7	9.5
Earnings Allocated to Common Shares Outstanding	$ 308.5			$ 375.4			$ 947.4	$ 1,133.7
Basic Net Income Per Common Share (in dollars per share)	$ 1.49			$ 1.80			$ 4.56	$ 5.44
Diluted Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	207,021,554			208,400,135			207,611,420	208,271,070
Plus: Dilutive Effect of Share-based Compensation (in shares)	231,438			488,437			316,300	587,906
Average Common and Potential Common Shares (in shares)	207,252,992			208,888,572			207,927,720	208,858,976
Earnings Allocated to Common and Potential Common Shares	$ 308.5			$ 375.4			$ 947.3	$ 1,133.7
Diluted Net Income Per Common Share (in dollars per share)	$ 1.49			$ 1.80			$ 4.56	$ 5.43
Common stock equivalents not included in the computation of diluted earnings per share because their inclusion would have been antidilutive (in shares)	48,596			0			129,239	0

Revenue from Contracts with C_3

Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,111.9	$ 1,078.7	$ 3,271.8	$ 3,390.5
Foreign Exchange Trading Income	51.8	64.7	154.9	223.2
Treasury Management Fees	7.5	9.3	23.8	31
Security Commissions and Trading Income	30.9	32.1	101.7	101.1
Other Operating Income	68.2	57.3	170.2	144
Investment Security Gains (Losses), net	0	(0.3)	6.9	(0.3)
Total Other Noninterest Income	158.4	163.1	457.5	499
Total Noninterest Income	1,270.3	1,241.8	3,729.3	3,889.5
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	459	435	1,358.7	1,383.4
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	574.1	565.3	1,673.4	1,765.8
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	20.7	21.7	61.3	62.2
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 58.1	$ 56.7	$ 178.4	$ 179.1

Revenue from Contracts with C_4

Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 1,111.9	$ 1,078.7	$ 3,271.8	$ 3,390.5
Security commissions and trading income	30.9	32.1	101.7	101.1
Other operating income	68.2	57.3	170.2	144
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	27.4	27.5	86.3	86.4
Other Operating Income
Disaggregation of Revenue [Line Items]
Trust, investment and other servicing fees	$ 11.2	$ 8.9	$ 30.5	$ 28.3

Revenue from Contracts with C_5

Revenue from Contracts with Clients (Contract Receivables) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Total Client Receivables	$ 960.4	$ 937.9
Trust Fees Receivable, net
Disaggregation of Revenue [Line Items]
Total Client Receivables	903	882.5
Contract with customer, asset, allowance for credit loss	14.6	13.5
Other
Disaggregation of Revenue [Line Items]
Total Client Receivables	$ 57.4	$ 55.4

Net Interest Income (Net Intere

Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Interest Income
Federal Reserve and Other Central Bank Deposits	$ 352.1	$ 135.4	$ 1,128	$ 212.2
Interest-Bearing Due from and Deposits with Banks	34.9	14.5	95.2	23.6
Federal Funds Sold	0	0	0.3	0
Securities Purchased under Agreements to Resell	463.9	30.5	874.1	38.4
Securities — Taxable	402.4	237	1,106.5	599.7
Securities - Non-Taxable	0.3	0.4	1	1.1
Loans and Leases	664.2	379.8	1,881.6	827.4
Other Interest-Earning Assets	17.2	1.7	38.7	5.2
Total Interest Income	1,935	799.3	5,125.4	1,707.6
Interest Expense
Deposits	716.6	177.3	1,914.7	184.6
Federal Funds Purchased	77.5	9.9	205.2	12.7
Securities Sold Under Agreements to Repurchase	454	25.5	843.5	31.8
Other Borrowings	154.8	35.7	446.3	47.2
Senior Notes	44.1	28.6	125.4	57.1
Long-Term Debt	31.8	9.3	91.4	21.5
Total Interest Expense	1,478.8	286.3	3,626.5	354.9
Net Interest Income	$ 456.2	$ 513	$ 1,498.9	$ 1,352.7

Other Operating Income - (Detai

Other Operating Income - (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Components of Other Operating Income [Line Items]
Other operating income	$ 68.2	$ 57.3	$ 170.2	$ 144
Loan Service Fees
Components of Other Operating Income [Line Items]
Other operating income	21.2	17.8	61.3	52.6
Banking Service Fees
Components of Other Operating Income [Line Items]
Other operating income	15	12.2	40.8	37.8
Bank Owned Life Insurance
Components of Other Operating Income [Line Items]
Other operating income	17.3	17.3	51	44
Other Income
Components of Other Operating Income [Line Items]
Other operating income	$ 14.7	$ 10	$ 17.1	$ 9.6

Other Operating Expense (Detail

Other Operating Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Other Income and Expenses [Abstract]
Business Promotion	$ 16.2	$ 20.1	$ 53.5	$ 49
Staff Related	11	7.8	27.7	16.9
FDIC Insurance Premiums	8.3	3.7	21.1	14.1
Charitable Contributions	3.8	5	11.3	12.1
Other Expenses	59.2	45.4	182.5	159.5
Total Other Operating Expense	$ 98.5	$ 82	$ 296.1	$ 251.6

Pension ((Benefit)) (Details)

Pension ((Benefit)) (Details) - Pension Plan - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
U.S. Plan | Qualified Plan
Defined Benefit Plan, Net Periodic Benefit Cost
Service Cost	$ 11,500,000	$ 11,100,000	$ 34,500,000	$ 37,500,000
Interest Cost	13,500,000	12,500,000	40,500,000	33,100,000
Expected Return on Plan Assets	(25,300,000)	(21,900,000)	(75,900,000)	(62,300,000)
Amortization
Actuarial Loss (Gain)	400,000	0	1,200,000	11,400,000
Prior Service Cost (Credit)	0	0	0	(100,000)
Total Pension (Benefit) Expense	100,000	1,700,000	300,000	19,600,000
Settlement Expense	0	17,000,000	0	37,300,000
Total Pension (Benefit) Expense	100,000	18,700,000	300,000	56,900,000
Contribution to pension plan			0	0
U.S. Plan | Non-Qualified Plan
Defined Benefit Plan, Net Periodic Benefit Cost
Service Cost	1,200,000	1,400,000	3,600,000	4,200,000
Interest Cost	1,300,000	1,000,000	3,900,000	3,000,000
Amortization
Actuarial Loss (Gain)	1,300,000	1,800,000	3,900,000	5,400,000
Total Pension (Benefit) Expense	3,800,000	4,200,000	11,400,000	12,600,000
Contribution to pension plan			16,500,000	20,700,000
Non-U.S. Plan
Defined Benefit Plan, Net Periodic Benefit Cost
Service Cost	400,000	400,000	1,100,000	1,300,000
Interest Cost	1,200,000	600,000	3,600,000	1,900,000
Expected Return on Plan Assets	(1,600,000)	(700,000)	(4,700,000)	(2,200,000)
Amortization
Actuarial Loss (Gain)	(100,000)	200,000	(300,000)	600,000
Total Pension (Benefit) Expense	(100,000)	500,000	(300,000)	1,600,000
Settlement Expense	0	0	0	700,000
Total Pension (Benefit) Expense	$ (100,000)	$ 500,000	$ (300,000)	$ 2,300,000

Share-Based Compensation Plan_2

Share-Based Compensation Plans (Compensation Expense for Share-Based Arrangements and Tax Impacts) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	$ 16.5	$ 14.8	$ 98.3	$ 104.8
Tax Benefits Recognized	4.2	3.7	24.7	26.3
Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	14.7	13.9	80.5	83.4
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total Share-Based Compensation Expense	$ 1.8	$ 0.9	$ 17.8	$ 21.4

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Affordable housing tax credits and other tax benefits	$ 28,500,000	$ 26,100,000	$ 85,100,000	$ 74,500,000
Investment company, voluntary fee waived	2,200,000	$ 2,600,000	6,500,000	$ 61,900,000
Contractual obligation to provide financial support	0		0
Fair value investments, seed capital investments					$ 19,900,000
Unfunded commitments	$ 0		$ 0		$ 0

Variable Interest Entities (Sum

Variable Interest Entities (Summary) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Variable Interest Entity [Line Items]
Assets	$ 146,330.6	$ 155,036.7
Liabilities	134,483.4	143,777.2
Other Assets
Variable Interest Entity [Line Items]
Total investment carrying amount	894.5	904.3
Other Assets | Affordable Housing
Variable Interest Entity [Line Items]
Total investment carrying amount	640.1	635.9
Other Assets | Other Community Development
Variable Interest Entity [Line Items]
Total investment carrying amount	254.4	268.4
Other Liabilities
Variable Interest Entity [Line Items]
Total unfunded commitments	205.5	218.9
Other Liabilities | Affordable Housing
Variable Interest Entity [Line Items]
Total unfunded commitments	205.5	218.9
Other Liabilities | Other Community Development
Variable Interest Entity [Line Items]
Total unfunded commitments	0	0
Variable Interest Entity, Not Primary Beneficiary | Other Assets
Variable Interest Entity [Line Items]
Assets	861.2	867.2
Variable Interest Entity, Not Primary Beneficiary | Other Liabilities
Variable Interest Entity [Line Items]
Liabilities	$ 198.5	$ 210.1

Commitments and Contingent Li_3

Commitments and Contingent Liabilities - Summary of Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 235,892.4	$ 162,025.4
OVER ONE YEAR	18,829.2	17,732.6
TOTAL	254,721.6	179,758
Undrawn Commitments
Loss Contingencies [Line Items]
Commitments, participated to others	222.5	266.6
Securities Lent with Indemnification
Loss Contingencies [Line Items]
ONE YEAR AND LESS	141,392.4	130,311
OVER ONE YEAR	0	0
TOTAL	141,392.4	130,311
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	33.4	35.1
Standby Letter of Credit and Financial Guarantee
Loss Contingencies [Line Items]
Guarantor obligations, current carrying value	61,400	16,300
Undrawn Commitments
Loss Contingencies [Line Items]
ONE YEAR AND LESS	12,409.2	13,639.2
OVER ONE YEAR	18,452.1	17,321.4
TOTAL	30,861.3	30,960.6
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	62,939	17,553
OVER ONE YEAR	375.8	409.9
TOTAL	63,314.8	17,962.9
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	24.5	25.4
OVER ONE YEAR	1.3	1.3
TOTAL	25.8	26.7
Reverse repurchase agreements
Loss Contingencies [Line Items]
ONE YEAR AND LESS	19,127.3	496.8
OVER ONE YEAR	0	0
TOTAL	$ 19,127.3	$ 496.8

Commitments and Contingent Li_4

Commitments and Contingent Liabilities (Narrative) (Details) shares in Millions		1 Months Ended		9 Months Ended	12 Months Ended
	Sep. 13, 2023 exchangeOffer	Jun. 30, 2016 USD ($) shares	Jun. 30, 2015 USD ($) shares	Sep. 30, 2023 USD ($) shares	Dec. 31, 2015 trust	Dec. 31, 2022 USD ($) shares
Loss Contingencies [Line Items]
Minimum securities lending related collateral percentage				100%
Commitments and letters of credit				$ 254,721,600,000		$ 179,758,000,000
Resell agreements, period end amounts excluding effects of agreements reported net by counterparty				19,100,000,000		496,800,000
Repurchase agreement counterparty, amount at risk				0		$ 0
Loss contingency accrual				0
Escrow deposit				$ 2,800,000,000
Visa Class A Common Stock
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
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
Potential exchange offer program, conversion period	90 days
Visa Class A Common Stock | Period Three
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
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]
Possible loss in future periods in excess of accrual				$ 80,000,000

Derivative Financial Instrume_3

Derivative Financial Instruments (Notional and Fair Values of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Derivative [Line Items]
NOTIONAL VALUE	$ 335,008.9	$ 310,684.3
FAIR VALUE, ASSET	2,470.7	3,151.2
Total Gross Derivatives, asset	3,413	3,732.4
Less: Netting	1,553.1	2,810.7
Derivative Assets	1,859.9	921.7
FAIR VALUE, LIABILITY	3,023.9	2,548.9
Derivative Liabilities	3,316.4	3,654.1
Less: Netting	2,409.9	1,865.9
Derivative Liabilities	906.5	1,788.2
Derivatives Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	10,320.5	8,537.9
FAIR VALUE, ASSET	260.1	349.4
FAIR VALUE, LIABILITY	44.4	51.1
Fair Value Hedges | Derivatives Designated as Hedging under GAAP | Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	5,566.1	4,622
FAIR VALUE, ASSET	82.8	58.5
FAIR VALUE, LIABILITY	43.2	32.7
Fair Value Hedges | Derivatives Not Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	324,688.4	302,146.4
FAIR VALUE, ASSET	3,152.9	3,383
FAIR VALUE, LIABILITY	3,272	3,603
Fair Value Hedges | Non-Designated Risk Management Derivatives
Derivative [Line Items]
NOTIONAL VALUE	818.6	773.6
FAIR VALUE, ASSET	0.7	0.4
FAIR VALUE, LIABILITY	29	34.9
Fair Value Hedges | Non-Designated Risk Management Derivatives | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	50.5	55.9
FAIR VALUE, ASSET	0.7	0.1
FAIR VALUE, LIABILITY	0.1	0.1
Fair Value Hedges | Non-Designated Risk Management Derivatives | Other Financial Derivatives
Derivative [Line Items]
NOTIONAL VALUE	768.1	717.7
FAIR VALUE, ASSET	0	0.3
FAIR VALUE, LIABILITY	28.9	34.8
Fair Value Hedges | Client-Related and Trading Derivatives
Derivative [Line Items]
NOTIONAL VALUE	323,869.8	301,372.8
FAIR VALUE, ASSET	3,152.2	3,382.6
FAIR VALUE, LIABILITY	3,243	3,568.1
Fair Value Hedges | Client-Related and Trading Derivatives | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	311,789.1	288,994.6
FAIR VALUE, ASSET	2,871.1	3,219.1
FAIR VALUE, LIABILITY	2,818.9	3,169
Fair Value Hedges | Client-Related and Trading Derivatives | Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	12,080.7	12,378.2
FAIR VALUE, ASSET	281.1	163.5
FAIR VALUE, LIABILITY	424.1	399.1
Cash Flow Hedges | Derivatives Designated as Hedging under GAAP | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	934.4	150.9
FAIR VALUE, ASSET	50.5	7.4
FAIR VALUE, LIABILITY	0	5.7
Net Investment Hedges | Derivatives Designated as Hedging under GAAP | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	3,820	3,765
FAIR VALUE, ASSET	126.8	283.5
FAIR VALUE, LIABILITY	$ 1.2	$ 12.7

Derivative Financial Instrume_4

Derivative Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Derivative [Line Items]
Gains or losses reclassified into earnings	$ 0	$ 0	$ 0	$ 0
Maximum length of time over which exposure was being hedged			4 months
Net investment gains (losses) recognized in AOCI	$ 129,900,000	$ 248,400,000	$ 66,800,000	$ 512,100,000
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			$ 50,500,000

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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 1,935	$ 799.3	$ 5,125.4	$ 1,707.6
Interest Expense	1,478.8	286.3	3,626.5	354.9
Other Operating Income	68.2	57.3	170.2	144
INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	11.1	(4)	34.7	(13.3)
Gains (Losses) on cash flow hedges recognized on	14.6	0	15.8	0.6
INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	(24.9)	(6.9)	(65.9)	18
Gains (Losses) on cash flow hedges recognized on	0	0	0	0
OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	0	0	0	0
Gains (Losses) on cash flow hedges recognized on	0.3	(0.6)	1.9	(4.4)
Interest Rate Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	14.1	32.3	0.6	90
Recognized on hedged items	(14.1)	(32.3)	(0.6)	(90)
Amounts related to interest settlements on derivatives	11.1	(4)	34.7	(13.3)
Interest Rate Contracts | INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(41.8)	(119.9)	(42.5)	(373.6)
Recognized on hedged items	41.8	119.9	42.5	373.6
Amounts related to interest settlements on derivatives	(24.9)	(6.9)	(65.9)	18
Interest Rate Contracts | OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	0	0	0	0
Recognized on hedged items	0	0	0	0
Amounts related to interest settlements on derivatives	0	0	0	0
Foreign Exchange Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on cash flow hedges recognized on	14.6	0	15.8	0.6
Foreign Exchange Contracts | INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on cash flow hedges recognized on	0	0	0	0
Foreign Exchange Contracts | OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on cash flow hedges recognized on	$ 0.3	$ (0.6)	$ 1.9	$ (4.4)

Derivative Financial Instrume_6

Derivative Financial Instruments (Hedged Items In Fair Value Hedges) (Details) - USD ($)	Sep. 30, 2023	Dec. 31, 2022
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Carrying value of the hedged items, available for sale debt securities	$ 2,631,600,000	$ 1,820,800,000
Cumulative hedge accounting basis adjustment, available for sale debt securities	(55,700,000)	(60,200,000)
Carrying value of the hedged items, senior notes and long-term subordinated debt	2,407,600,000	2,746,200,000
Cumulative hedge accounting basis adjustment, senior notes and long-term subordinated debt	(336,500,000)	(294,000,000)
Hedged asset fair value hedge discontinued cumulative increase decrease	2,200,000	7,300,000
Hedged liability fair value hedge discontinued cumulative increase decrease	$ 0	$ 0

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		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Derivatives Not Designated as Hedging under GAAP
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 56.8	$ 67.7	$ 147.6	$ 218.9
Non-Designated Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	3.8	0.1	(15.4)	(11.4)
Non-Designated Risk Management Derivatives | Foreign Exchange Contracts
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 1.4	$ (0.6)	$ 2.9	$ (2)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Operating Income	Other Operating Income	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	$ 2.4	$ 0.7	$ (18.3)	$ (9.4)
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Operating Income	Other Operating Income	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	$ 53	$ 67.6	$ 163	$ 230.3
Client-Related and Trading Derivatives | Foreign Exchange Contracts
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 51.8	$ 64.7	$ 154.9	$ 223.2
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Foreign Exchange Trading Income	Foreign Exchange Trading Income	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	$ 2.9	$ 8.1	$ 7.1
Derivative, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Security Commissions and Trading Income	Security Commissions and Trading Income	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) - OVERNIGHT AND CONTINUOUS - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	$ 545.9	$ 567.2
Net Amount of Recognized Liabilities for Repurchase Agreements in Note 23	545.9	567.2
U.S. Treasury and Agency Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	$ 545.9	$ 567.2

Offsetting of Assets and Liab_3

Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 2,470.7	$ 3,151.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,553.1	2,810.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	917.6	340.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	14.3	5
NET AMOUNT	903.3	335.5
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	942.3	581.2
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	942.3	581.2
Total Derivatives
GROSS RECOGNIZED ASSETS	3,413	3,732.4
Derivative Assets	1,859.9	921.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	14.3	5
NET AMOUNT	1,845.6	916.7
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	50,143.2	12,494.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	49,758.9	11,423.9
Securities Purchased under Agreements to Resell	384.3	1,070.3
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	384.3	1,070.3
Other assets excluding derivatives and non financial instruments	10,700	8,900
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	2,106.8	2,928.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,266.6	2,666.4
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	840.2	262.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	14.3	5
NET AMOUNT	825.9	257.5
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	363.9	217.6
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	286.5	144.3
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	77.4	73.3
NET AMOUNT	$ 77.4	73.3
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS		4.4
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		4.4
NET AMOUNT		4.4
Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS		0.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		0.3
NET AMOUNT		$ 0.3

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	Sep. 30, 2023	Dec. 31, 2022
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	$ 3,023.9	$ 2,548.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,409.9	1,865.9
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	614	683
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
Net Amount	614	683
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	292.5	1,105.2
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0
NET AMOUNT	292.5	1,105.2
Offsetting Derivative Liabilities [Abstract]
GROSS RECOGNIZED LIABILITIES	3,316.4	3,654.1
Derivative Liabilities	906.5	1,788.2
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	906.5	1,788.2
Securities Sold under Agreements to Repurchase(2)
GROSS RECOGNIZED LIABILITIES	50,304.8	11,991.1
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	49,758.9	11,423.9
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	545.9	567.2
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	545.9	567.2
Other liabilities	3,700	3,200
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	2,527.7	2,082.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,380.6	1,826.7
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	147.1	255.6
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
Net Amount	147.1	255.6
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	467.3	426.5
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2.1	5.9
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	465.2	420.6
Net Amount	465.2	420.6
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES		5.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		5.3
Net Amount		5.3
Other Financial Derivatives | Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	28.9	34.8
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	27.2	33.3
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	1.7	1.5
Net Amount	$ 1.7	$ 1.5

Offsetting of Assets and Liab_5

Offsetting of Assets and Liabilities (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Offsetting Assets and Liabilities [Line Items]
Collateral received	$ 14.3	$ 5
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	592.2	190.9
Collateral deposited with derivative counterparties for derivatives instruments with credit-risk-related contingent features that are in a liability position	548.9	55.1
Net maximum amount of termination payments that could have been required	43.3	135.8
Net Investment Hedges
Offsetting Assets and Liabilities [Line Items]
Collateral received	67.7
Gross amounts not offset in the balance sheet	$ 473.4
Cash collateral received from derivative counterparties and not offset against derivative assets		131.8
Cash collateral deposited with derivative counterparties not offset against derivative liabilities		$ 26.3