Northern Trust (NTRS) 10-Q 27 Apr 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page	3 Months Ended
	Mar. 31, 2021shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
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)	208,140,239
Amendment Flag	false
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Entity Central Index Key	0000073124
Current Fiscal Year End Date	--12-31
Common Stock, $1.66 2/3 Par Value
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, $1.66 2/3 Par Value
Trading Symbol	NTRS
Security Exchange Name	NASDAQ
Depositary Shares, each representing 1/1,000th interest in a share of Series E Non-Cumulative Perpetual Preferred Stock
Entity Information [Line Items]
Title of 12(b) Security	Depositary Shares, each representing 1/1,000th interest in a share of Series E Non-Cumulative Perpetual Preferred Stock
Trading Symbol	NTRSO
Security Exchange Name	NASDAQ

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
ASSETS
Cash and Due from Banks	$ 4,584.4	$ 4,389.5
Federal Reserve and Other Central Bank Deposits	46,911.4	55,503.6
Interest-Bearing Deposits with Banks	5,142.8	4,372.6
Federal Funds Sold	0.1	0
Securities Purchased under Agreements to Resell	1,109.3	1,596.5
Debt Securities
Available for Sale (Amortized cost of $42,508.6 and $41,155.7)	42,878.6	42,022
Held to Maturity	17,136.4	17,791.1
Trading Account	0.4	0.5
Total Debt Securities	60,015.4	59,813.6
Loans and Leases
TOTAL LOANS AND LEASES	34,344.3	33,759.7
Allowance for Credit Losses	(175.7)	(198.8)
Buildings and Equipment	496.7	514.9
Client Security Settlement Receivables	1,970.2	1,160.2
Goodwill	704	707.2
Other Assets	8,821.2	8,384.9
Total Assets	163,924.1	170,003.9
Deposits
Demand and Other Noninterest-Bearing	18,863.1	17,728.5
Savings, Money Market and Other Interest-Bearing	27,322.9	28,631.8
Savings Certificates and Other Time	909.7	937.1
Non U.S. Offices — Noninterest-Bearing	26,615.2	25,382.2
Non U.S. Offices — Interest-Bearing	63,746.5	71,198.4
Total Deposits	137,457.4	143,878
Federal Funds Purchased	0.2	260.2
Securities Sold Under Agreements to Repurchase	95.6	39.8
Other Borrowings	5,428.4	4,011.5
Senior Notes	2,991.2	3,122.4
Long-Term Debt	1,165.9	1,189.3
Floating Rate Capital Debt	277.8	277.8
Other Liabilities	5,049.7	5,536.6
Total Liabilities	152,466.2	158,315.6
STOCKHOLDERS' EQUITY
Common Stock	408.6	408.6
Additional Paid-In Capital	914.1	963.6
Retained Earnings	12,415.6	12,207.7
Accumulated Other Comprehensive Income (Loss)	65.9	428
Treasury Stock	(3,231.2)	(3,204.5)
Total Stockholders’ Equity	11,457.9	11,688.3
Total Liabilities and Stockholders’ Equity	163,924.1	170,003.9
Series D Preferred Stock
STOCKHOLDERS' EQUITY
Preferred Stock	493.5	493.5
Total Stockholders’ Equity	493.5	493.5
Series E Preferred Stock
STOCKHOLDERS' EQUITY
Preferred Stock	391.4	391.4
Total Stockholders’ Equity	391.4	391.4
Commercial
Loans and Leases
TOTAL LOANS AND LEASES	15,847.9	15,262
Personal
Loans and Leases
TOTAL LOANS AND LEASES	$ 18,496.4	$ 18,497.7

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Available-for-sale securities, amortized cost	$ 42,508.6	$ 41,155.7
Held to maturity, fair value	17,100	17,797.4
Unearned income	$ 9.4	$ 9.8
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)	208,140,239	208,289,178
Treasury stock (in shares)	37,031,285	36,882,346
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 - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,063.7	$ 1,003.6
Foreign Exchange Trading Income	78.7	88.9
Treasury Management Fees	11.2	11
Security Commissions and Trading Income	34.8	41.7
Other Operating Income	54.9	34.4
Investment Security Gains (Losses), net	0	0
Total Noninterest Income	1,243.3	1,179.6
Net Interest Income
Interest Income	349.9	529.2
Interest Expense	9.8	121.1
Net Interest Income	340.1	408.1
Provision for Credit Losses	(30)	61
Net Interest Income after Provision for Credit Losses	370.1	347.1
Noninterest Expense
Compensation	518.5	499.8
Employee Benefits	103.4	97.9
Outside Services	196.4	192.8
Equipment and Software	176.7	162.2
Occupancy	50.8	51.1
Other Operating Expense	71.7	61.8
Total Noninterest Expense	1,117.5	1,065.6
Income before Income Taxes	495.9	461.1
Provision for Income Taxes	120.8	100.5
Net Income	375.1	360.6
Preferred Stock Dividends	16.2	30.5
Net Income Applicable to Common Stock	$ 358.9	$ 330.1
Per Common Share
Net Income — Basic (in dollars per share)	$ 1.71	$ 1.56
Net Income - Diluted (in dollars per share)	$ 1.70	$ 1.55
Average number of common shares outstanding
Average Number of Common Shares Outstanding - Basic (in shares)	208,112,824	208,881,131
Average Number of Common Shares Outstanding - Diluted (in shares)	208,946,448	209,816,822

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net Income	$ 375.1	$ 360.6
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized Gains (Losses) on Debt Securities Available for Sale	(369.7)	199.7
Net Unrealized Gains (Losses) on Cash Flow Hedges	(5.2)	7.3
Net Foreign Currency Adjustments	5	25.7
Net Pension and Other Postretirement Benefit Adjustments	7.8	7
Net Change	(362.1)	239.7
Comprehensive Income	$ 13	$ 600.3

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Cumulative Effect Adjustment	PREFERRED STOCK	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	RETAINED EARNINGS	RETAINED EARNINGSCumulative Effect Adjustment	ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS)	TREASURY STOCK
Beginning balance at Dec. 31, 2019	$ 11,091	$ (10.1)	$ 1,273.4	$ 408.6	$ 1,013.1	$ 11,656.7	$ (10.1)	$ (194.7)	$ (3,066.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	360.6					360.6
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	239.7							239.7
Dividends [Abstract]
Common Stock	(148.6)					(148.6)
Preferred Stock	(19)					(19)
Redemption of Preferred Stock, Series C	(400)		(388.5)			(11.5)
Stock Awards and Options Exercised	62.9				(74.8)				137.7
Stock Purchased	(296.8)								(296.8)
Ending balance at Mar. 31, 2020	10,879.7		884.9	408.6	938.3	11,828.1		45	(3,225.2)
Beginning balance at Dec. 31, 2020	11,688.3		884.9	408.6	963.6	12,207.7		428	(3,204.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	375.1					375.1
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)	(362.1)							(362.1)
Dividends [Abstract]
Common Stock	(151)					(151)
Preferred Stock	(16.2)					(16.2)
Stock Awards and Options Exercised	59.4				(49.5)				108.9
Stock Purchased	(135.6)								(135.6)
Ending balance at Mar. 31, 2021	$ 11,457.9		$ 884.9	$ 408.6	$ 914.1	$ 12,415.6		$ 65.9	$ (3,231.2)

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Stockholders' Equity [Abstract]
Common stock dividends (in usd per share)	$ 0.70	$ 0.70

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
CASH FLOWS FROM OPERATING ACTIVITIES
Net Income	$ 375.1	$ 360.6
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Amortization and Accretion of Securities and Unearned Income, net	26.1	22.4
Provision for Credit Losses	(30)	61
Depreciation and Amortization	125.4	123.8
Pension Plan Contributions	(6.7)	(10.6)
Change in Receivables	(66.7)	(122.7)
Change in Interest Payable	7.3	(5.7)
Change in Collateral With Derivative Counterparties, net	(824.2)	(3,570.2)
Other Operating Activities, net	462	456.1
Net Cash Provided by (Used in) Operating Activities	68.3	(2,685.3)
CASH FLOWS FROM INVESTING ACTIVITIES
Change in Federal Funds Sold	(0.1)	5
Change in Securities Purchased under Agreements to Resell	477.9	(367.2)
Change in Interest-Bearing Deposits with Banks	(772.6)	(757.6)
Net Change in Federal Reserve and Other Central Bank Deposits	8,369.3	(11,204.7)
Purchases of Debt Securities – Held to Maturity	(16,047.6)	(7,076)
Proceeds from Maturity and Redemption of Debt Securities – Held to Maturity	16,125.8	6,287.3
Purchases of Debt Securities – Available for Sale	(3,631.9)	(2,857.6)
Proceeds from Sale, Maturity and Redemption of Debt Securities – Available for Sale	2,214.9	2,430.7
Change in Loans and Leases	(592.4)	(6,432.9)
Purchases of Buildings and Equipment	(10.7)	(37.6)
Purchases and Development of Computer Software	(94.8)	(94.8)
Change in Client Security Settlement Receivables	(810.4)	(1,241.9)
Other Investing Activities, net	(93.7)	(153)
Net Cash Provided by (Used in) Investing Activities	5,133.7	(21,500.3)
CASH FLOWS FROM FINANCING ACTIVITIES
Change in Deposits	(5,844.1)	23,956.5
Change in Federal Funds Purchased	(260)	3,817.7
Change in Securities Sold under Agreements to Repurchase	55.8	(455.6)
Change in Short-Term Other Borrowings	1,420.3	(778)
Redemption of Preferred Stock - Series C	0	(400)
Treasury Stock Purchased	(135.6)	(296.8)
Net Proceeds from Stock Options	8.7	8.8
Cash Dividends Paid on Common Stock	(145.9)	(147.1)
Cash Dividends Paid on Preferred Stock	(4.7)	(5.8)
Other Financing Activities, net	(0.1)	8.3
Net Cash (Used in) Provided by Financing Activities	(4,905.6)	25,708
Effect of Foreign Currency Exchange Rates on Cash	(101.5)	(148.4)
Change in Cash and Due from Banks	194.9	1,374
Cash and Due from Banks at Beginning of Period	4,389.5	4,459.2
Cash and Due from Banks at End of Period	4,584.4	5,833.2
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION
Interest Paid	2.2	126.7
Income Taxes Paid	30.8	72.6
Transfers from Loans to OREO	$ 3.3	$ (0.2)

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2021
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 March 31, 2021 and 2020, 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. The consolidated statements of income include results of acquired subsidiaries from the dates of acquisition. Certain prior-period balances have been reclassified to conform with the current year’s presentation. 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, 2020.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2021
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements On January 1, 2021, Northern Trust adopted Accounting Standards Update (ASU) No. 2020-01, “Investments—Equity Securities (Topic 321), Investments—Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815): Clarifying the Interactions between Topic 321, Topic 323, and Topic 815” (ASU 2020-01). ASU 2020-01 addresses two accounting issues: (1) application of the measurement alternative under Topic 321 in correlation with the transition into and out of the equity method under Topic 323 and (2) the measurement of certain forward contracts and purchased options to acquire equity securities. ASU 2020-01 clarifies that an entity applying the measurement alternative under Topic 321 that must transition to the equity method under Topic 323 because of an observable transaction will remeasure its investment immediately before transition, whereas an entity applying the equity method under Topic 323 that must transition to Topic 321 because of an observable transaction will remeasure its investment immediately after transition. ASU 2020-01 also clarifies that certain forward contracts or purchased call options to acquire equity securities generally will be measured using the fair value principles of Topic 321 before settlement or exercise. Upon adoption of ASU 2020-01, there was no significant impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. On January 1, 2021, Northern Trust adopted ASU No. 2020-08, “Codification Improvements to Subtopic 310-20, Receivables—Nonrefundable Fees and Other Costs” (ASU 2020-08). ASU 2020-08 clarifies the Codification related to the standard issued in ASU No. 2017-08, “Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities”. ASU 2020-08 clarifies that an entity should amortize premiums on purchased callable debt securities to the first call date and related call amount and at that point reassess if there is a remaining premium to amortize to a subsequent call date. Upon adoption of ASU 2020-08, there was no significant impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. On January 7, 2021, Northern Trust retrospectively adopted ASU No. 2021-01, “Reference Rate Reform (Topic 848): Scope” (ASU 2021-01). ASU 2021-01 clarifies the scope of Topic 848 to explicitly include those derivative instruments affected by changes in interest rates used for margining, discounting, or contract price alignment as eligible for certain optional expedients and exceptions in Topic 848. Upon adoption of ASU 2021-01, Northern Trust elected the expedients provided in Topic 848 with no significant impact on Northern Trust’s consolidated balance sheets or consolidated statements of income.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair Value Hierarchy. The following describes the hierarchy of valuation inputs (Levels 1, 2, and 3) used to measure fair value and the primary valuation methodologies used by Northern Trust for financial instruments measured at fair value on a recurring basis. Observable inputs reflect market data obtained from sources independent of the reporting entity; unobservable inputs reflect the entity’s own assumptions about how market participants would value an asset or liability based on the best information available. GAAP requires an entity measuring fair value to maximize the use of observable inputs and minimize the use of unobservable inputs and establishes a fair value hierarchy of inputs. Financial instruments are categorized within the hierarchy based on the lowest level input that is significant to their valuation. No transfers into or out of Level 3 occurred during the three months ended March 31, 2021 or the twelve months ended December 31, 2020. Level 1 — Quoted, active market prices for identical assets or liabilities. Northern Trust’s Level 1 assets are comprised of available for sale 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 available for sale and 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 pre-determined tolerance levels that are assigned based on an asset type’s characteristics, the exception is researched and, if the price is not able to be validated, an alternate pricing vendor is utilized, consistent with Northern Trust’s pricing source hierarchy. As of March 31, 2021, Northern Trust’s available for sale debt securities portfolio included 2,471 Level 2 debt securities with an aggregate market value of $40.3 billion. All 2,471 debt securities were valued by external pricing vendors. As of December 31, 2020, Northern Trust’s available for sale debt securities portfolio included 2,260 Level 2 debt securities with an aggregate market value of $39.2 billion. All 2,260 debt securities were valued by external pricing vendors. Trading account debt securities, which totaled $0.4 million and $0.5 million as of March 31, 2021 and December 31, 2020, respectively, were all valued using 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; credit spreads, default probabilities, and recovery rates for credit default swap 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 21 — Commitments and Contingent Liabilities for further information. Northern Trust believes its valuation methods for its assets and liabilities carried at fair value are appropriate; however, the use of different methodologies or assumptions, particularly as applied to Level 3 assets and liabilities, could have a material effect on the computation of their estimated fair values. The following table presents the fair values of Northern Trust’s Level 3 liabilities as of March 31, 2021 and December 31, 2020, 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 29: LEVEL 3 SIGNIFICANT UNOBSERVABLE INPUTS MARCH 31, 2021 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 $34.6 million Discounted Cash Flow Conversion Rate 1.62x 1.62x Visa Class A Appreciation 9.63% 9.63% Expected Duration 12 - 33 months 20 months (1) Weighted average of expected duration based on scenario probability. DECEMBER 31, 2020 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 $35.3 million Discounted Cash Flow Conversion Rate 1.62x 1.62x Visa Class A Appreciation 8.73% 8.73% 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 March 31, 2021 and December 31, 2020, segregated by fair value hierarchy level. TABLE 30: RECURRING BASIS HIERARCHY LEVELING MARCH 31, 2021 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 2,561.0 $ — $ — $ — $ 2,561.0 Obligations of States and Political Subdivisions — 3,279.8 — — 3,279.8 Government Sponsored Agency — 24,650.7 — — 24,650.7 Non-U.S. Government — 558.1 — — 558.1 Corporate Debt — 2,398.7 — — 2,398.7 Covered Bonds — 544.1 — — 544.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 3,003.4 — — 3,003.4 Other Asset-Backed — 4,783.0 — — 4,783.0 Commercial Mortgage-Backed — 1,099.8 — — 1,099.8 Total Available for Sale 2,561.0 40,317.6 — — 42,878.6 Trading Account — 0.4 — — 0.4 Total Available for Sale and Trading Debt Securities 2,561.0 40,318.0 — — 42,879.0 Other Assets Derivative Assets Foreign Exchange Contracts — 3,001.0 — (1,973.5) 1,027.5 Interest Rate Contracts — 205.6 — (3.6) 202.0 Total Derivative Assets — 3,206.6 — (1,977.1) 1,229.5 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 2,543.0 — (2,023.7) 519.3 Interest Rate Contracts — 123.7 — (66.6) 57.1 Other Financial Derivatives (1) — — 34.6 — 34.6 Total Derivative Liabilities $ — $ 2,666.7 $ 34.6 $ (2,090.3) $ 611.0 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of March 31, 2021, derivative assets and liabilities shown above also include reductions of $449.1 million and $562.3 million, 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, 2020 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 2,799.9 $ — $ — $ — $ 2,799.9 Obligations of States and Political Subdivisions — 3,083.6 — — 3,083.6 Government Sponsored Agency — 24,956.7 — — 24,956.7 Non-U.S. Government — 714.0 — — 714.0 Corporate Debt — 2,539.6 — — 2,539.6 Covered Bonds — 553.1 — — 553.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,345.8 — — 2,345.8 Other Asset-Backed — 3,997.5 — — 3,997.5 Commercial Mortgage-Backed — 1,031.8 — — 1,031.8 Total Available for Sale 2,799.9 39,222.1 — — 42,022.0 Trading Account — 0.5 — — 0.5 Total Available for Sale and Trading Debt Securities 2,799.9 39,222.6 — — 42,022.5 Other Assets Derivative Assets Foreign Exchange Contracts — 4,260.7 — (3,505.3) 755.4 Interest Rate Contracts — 297.5 — (2.5) 295.0 Total Derivative Assets — 4,558.2 — (3,507.8) 1,050.4 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 4,722.5 — (2,718.6) 2,003.9 Interest Rate Contracts — 125.0 — (98.5) 26.5 Other Financial Derivatives (1) — — 35.3 — 35.3 Total Derivative Liabilities $ — $ 4,847.5 $ 35.3 $ (2,817.1) $ 2,065.7 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, 2020, derivative assets and liabilities shown above also include reductions of $1,867.8 million and $1,177.2 million, 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. The following table presents the changes in Level 3 liabilities for the three months ended March 31, 2021 and 2020. TABLE 31: CHANGES IN LEVEL 3 LIABILITIES (In Millions) SWAPS RELATED TO SALE OF CERTAIN VISA CLASS B COMMON SHARES THREE MONTHS ENDED MARCH 31, 2021 2020 Fair Value at January 1 $ 35.3 $ 33.4 Total (Gains) Losses: Included in Earnings (1) 3.6 (2.9) Purchases, Issues, Sales, and Settlements Settlements (4.3) (4.0) Fair Value at March 31 $ 34.6 $ 26.5 (1) (Gains) losses are recorded in Other Operating Income on the consolidated statements of income. Carrying values of assets and liabilities that are not measured at fair value on a recurring basis may be adjusted to fair value in periods subsequent to their initial recognition, for example, to record an impairment of an asset. GAAP requires entities to separately disclose these subsequent fair value measurements and to classify them under the fair value hierarchy. Assets measured at fair value on a nonrecurring basis at March 31, 2021 and December 31, 2020, 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 discount factors ranging from 15.0% to 20.0% with a weighted average based on fair values of 15.8% and 16.8% as of March 31, 2021 and December 31, 2020, 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-based nonaccrual loans that have been adjusted to fair value totaled $16.7 million and $24.6 million at March 31, 2021 and December 31, 2020, 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 March 31, 2021 and December 31, 2020, 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 32: LEVEL 3 NONRECURRING BASIS SIGNIFICANT UNOBSERVABLE INPUTS MARCH 31, 2021 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $16.7 million Market Approach Discount factor applied to real estate collateral-based loans to reflect realizable value 15.0% - 20.0% 15.8% (1) Includes real estate collateral-based loans and other collateral-based loans. DECEMBER 31, 2020 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $24.6 million Market Approach Discount factor applied to real estate collateral-based loans to reflect realizable value 15.0 % - 20.0% 16.8% (1) Includes real estate collateral-based loans and other collateral-based loans. The following table summarizes the fair values of all financial instruments. TABLE 33: FAIR VALUE OF FINANCIAL INSTRUMENTS MARCH 31, 2021 FAIR VALUE (In Millions) BOOK VALUE TOTAL FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 ASSETS Cash and Due from Banks $ 4,584.4 $ 4,584.4 $ 4,584.4 $ — $ — Federal Reserve and Other Central Bank Deposits 46,911.4 46,911.4 — 46,911.4 — Interest-Bearing Deposits with Banks 5,142.8 5,142.8 — 5,142.8 — Federal Funds Sold 0.1 0.1 — 0.1 — Securities Purchased under Agreements to Resell 1,109.3 1,109.3 — 1,109.3 — Debt Securities Available for Sale (1) 42,878.6 42,878.6 2,561.0 40,317.6 — Held to Maturity 17,136.4 17,100.0 100.0 17,000.0 — Trading Account 0.4 0.4 — 0.4 — Loans (excluding Leases) Held for Investment 34,168.1 34,181.7 — — 34,181.7 Client Security Settlement Receivables 1,970.2 1,970.2 — 1,970.2 — Other Assets Federal Reserve and Federal Home Loan Bank Stock 230.0 230.0 — 230.0 — Community Development Investments 908.1 908.1 — 908.1 — Employee Benefit and Deferred Compensation 230.3 234.5 133.9 100.6 — LIABILITIES Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 72,801.2 $ 72,801.2 $ 72,801.2 $ — $ — Savings Certificates and Other Time 909.7 911.0 — 911.0 — Non U.S. Offices Interest-Bearing 63,746.5 63,746.5 — 63,746.5 — Federal Funds Purchased 0.2 0.2 — 0.2 — Securities Sold Under Agreements to Repurchase 95.6 95.6 — 95.6 — Other Borrowings 5,428.4 5,428.6 — 5,428.6 — Senior Notes 2,991.2 3,083.9 — 3,083.9 — Long-Term Debt Subordinated Debt 1,165.9 1,211.5 — 1,211.5 — Floating Rate Capital Debt 277.8 268.7 — 268.7 — Other Liabilities Standby Letters of Credit 18.7 18.7 — — 18.7 Loan Commitments 76.9 76.9 — — 76.9 Derivative Instruments Asset/Liability Management Foreign Exchange Contracts Assets $ 370.9 $ 370.9 $ — $ 370.9 $ — Liabilities 29.3 29.3 — 29.3 — Interest Rate Contracts Assets 10.0 10.0 — 10.0 — Liabilities 13.7 13.7 — 13.7 — Other Financial Derivatives Liabilities (2) 34.6 34.6 — — 34.6 Client-Related and Trading Foreign Exchange Contracts Assets 2,630.1 2,630.1 — 2,630.1 — Liabilities 2,513.7 2,513.7 — 2,513.7 — Interest Rate Contracts Assets 195.6 195.6 — 195.6 — Liabilities 110.0 110.0 — 110.0 — (1) Refer to the table located on page 34 for the disaggregation of available for sale debt securities. (2) This line consists of swaps related to the sale of certain Visa Class B common shares. DECEMBER 31, 2020 FAIR VALUE (In Millions) BOOK VALUE TOTAL FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 ASSETS Cash and Due from Banks $ 4,389.5 $ 4,389.5 $ 4,389.5 $ — $ — Federal Reserve and Other Central Bank Deposits 55,503.6 55,503.6 — 55,503.6 — Interest-Bearing Deposits with Banks 4,372.6 4,372.6 — 4,372.6 — Securities Purchased under Agreements to Resell 1,596.5 1,596.5 — 1,596.5 — Debt Securities Available for Sale (1) 42,022.0 42,022.0 2,799.9 39,222.1 — Held to Maturity 17,791.1 17,797.4 90.0 17,707.4 — Trading Account 0.5 0.5 — 0.5 — Loans (excluding Leases) Held for Investment 33,558.0 34,017.5 — — 34,017.5 Client Security Settlement Receivables 1,160.2 1,160.2 — 1,160.2 — Other Assets Federal Reserve and Federal Home Loan Bank Stock 275.0 275.0 — 275.0 — Community Development Investments 919.6 919.6 — 919.6 — Employee Benefit and Deferred Compensation 215.8 228.9 138.6 90.3 — LIABILITIES Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 71,742.5 $ 71,742.5 $ 71,742.5 $ — $ — Savings Certificates and Other Time 937.1 943.0 — 943.0 — Non U.S. Offices Interest-Bearing 71,198.4 71,198.4 — 71,198.4 — Federal Funds Purchased 260.2 260.2 — 260.2 — Securities Sold Under Agreements to Repurchase 39.8 39.8 — 39.8 — Other Borrowings 4,011.5 4,012.7 — 4,012.7 — Senior Notes 3,122.4 3,222.6 — 3,222.6 — Long-Term Debt Subordinated Debt 1,189.3 1,250.1 — 1,250.1 — Floating Rate Capital Debt 277.8 264.6 — 264.6 — Other Liabilities Standby Letters of Credit 22.4 22.4 — — 22.4 Loan Commitments 77.0 77.0 — — 77.0 Derivative Instruments Asset/Liability Management Foreign Exchange Contracts Assets $ 15.6 $ 15.6 $ — $ 15.6 $ — Liabilities 311.8 311.8 — 311.8 — Interest Rate Contracts Assets 8.3 8.3 — 8.3 — Liabilities 10.2 10.2 — 10.2 — Other Financial Derivatives Liabilities (2) 35.3 35.3 — — 35.3 Client-Related and Trading Foreign Exchange Contracts Assets 4,245.1 4,245.1 — 4,245.1 — Liabilities 4,410.7 4,410.7 — 4,410.7 — Interest Rate Contracts Assets 289.2 289.2 — 289.2 — Liabilities 114.8 114.8 — 114.8 — (1) Refer to the table located on page 35 for the disaggregation of available for sale debt securities. (2) This line consists of swaps related to the sale of certain Visa Class B common shares.

Securities

Securities	3 Months Ended
	Mar. 31, 2021
Investments, Debt and Equity Securities [Abstract]
Securities	Securities Debt Securities Available for Sale. The following tables provide the amortized cost and fair values at March 31, 2021 and December 31, 2020, and remaining maturities of debt securities available for sale at March 31, 2021. TABLE 34: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF DEBT SECURITIES AVAILABLE FOR SALE MARCH 31, 2021 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 2,521.1 $ 50.6 $ 10.7 $ 2,561.0 Obligations of States and Political Subdivisions 3,249.8 82.5 52.5 3,279.8 Government Sponsored Agency 24,535.5 275.4 160.2 24,650.7 Non-U.S. Government 564.3 0.1 6.3 558.1 Corporate Debt 2,336.3 65.2 2.8 2,398.7 Covered Bonds 535.8 8.3 — 544.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,968.8 54.0 19.4 3,003.4 Other Asset-Backed 4,749.5 38.0 4.5 4,783.0 Commercial Mortgage-Backed 1,047.5 53.6 1.3 1,099.8 Total $ 42,508.6 $ 627.7 $ 257.7 $ 42,878.6 DECEMBER 31, 2020 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 2,728.8 $ 71.1 $ — $ 2,799.9 Obligations of States and Political Subdivisions 2,927.8 155.9 0.1 3,083.6 Government Sponsored Agency 24,595.1 388.5 26.9 24,956.7 Non-U.S. Government 713.6 1.1 0.7 714.0 Corporate Debt 2,459.9 79.8 0.1 2,539.6 Covered Bonds 543.1 10.0 — 553.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,281.7 64.7 0.6 2,345.8 Other Asset-Backed 3,953.5 46.8 2.8 3,997.5 Commercial Mortgage-Backed 952.2 79.7 0.1 1,031.8 Total $ 41,155.7 $ 897.6 $ 31.3 $ 42,022.0 TABLE 35: REMAINING MATURITY OF DEBT SECURITIES AVAILABLE FOR SALE MARCH 31, 2021 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 $ 99.9 $ 101.5 $ 1,874.1 $ 1,911.3 $ 547.1 $ 548.2 $ — $ — $ 2,521.1 $ 2,561.0 Obligations of States and Political Subdivisions 7.2 7.3 294.8 308.4 2,764.2 2,787.5 183.6 176.6 3,249.8 3,279.8 Government Sponsored Agency 4,859.6 4,913.7 8,260.4 8,330.3 8,833.7 8,816.8 2,581.8 2,589.9 24,535.5 24,650.7 Non-U.S. Government 269.6 269.6 40.5 40.5 254.2 248.0 — — 564.3 558.1 Corporate Debt 372.6 376.5 1,950.5 2,009.1 9.3 9.2 3.9 3.9 2,336.3 2,398.7 Covered Bonds 106.8 107.1 429.0 437.0 — — — — 535.8 544.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 534.4 537.5 2,001.7 2,043.0 432.7 422.9 — — 2,968.8 3,003.4 Other Asset-Backed 733.9 742.4 3,201.6 3,228.2 739.2 737.8 74.8 74.6 4,749.5 4,783.0 Commercial Mortgage-Backed 17.8 17.8 510.0 532.5 511.6 541.4 8.1 8.1 1,047.5 1,099.8 Total $ 7,001.8 $ 7,073.4 $ 18,562.6 $ 18,840.3 $ 14,092.0 $ 14,111.8 $ 2,852.2 $ 2,853.1 $ 42,508.6 $ 42,878.6 Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments. Debt Securities Available for Sale with Unrealized Losses. The following table provides information regarding debt securities available for sale with no credit losses reported that had been in a continuous unrealized loss position for less than twelve months and for twelve months or longer as of March 31, 2021 and December 31, 2020. TABLE 36: DEBT SECURITIES AVAILABLE FOR SALE IN UNREALIZED LOSS POSITION WITH NO CREDIT LOSSES REPORTED AS OF MARCH 31, 2021 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ 237.6 $ 10.7 $ — $ — $ 237.6 $ 10.7 Obligations of States and Political Subdivisions 1,456.8 52.5 — — 1,456.8 52.5 Government Sponsored Agency 5,915.6 148.5 2,096.4 11.7 8,012.0 160.2 Non-U.S. Government 274.4 6.3 — — 274.4 6.3 Corporate Debt 272.6 2.8 — — 272.6 2.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 981.3 19.4 49.9 — 1,031.2 19.4 Other Asset-Backed 1,035.7 4.5 60.0 — 1,095.7 4.5 Commercial Mortgage-Backed 120.8 1.2 7.5 0.1 128.3 1.3 Total $ 10,294.8 $ 245.9 $ 2,213.8 $ 11.8 $ 12,508.6 $ 257.7 AS OF DECEMBER 31, 2020 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED Obligations of States and Political Subdivisions $ 52.3 $ 0.1 $ — $ — $ 52.3 $ 0.1 Government Sponsored Agency 2,402.3 13.6 2,528.7 13.3 4,931.0 26.9 Non-U.S. Government 90.5 0.7 — — 90.5 0.7 Corporate Debt 66.6 0.1 — — 66.6 0.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 162.8 0.5 49.9 0.1 212.7 0.6 Other Asset-Backed 176.8 0.2 792.3 2.6 969.1 2.8 Commercial Mortgage-Backed 44.4 0.1 — — 44.4 0.1 Total $ 2,995.7 $ 15.3 $ 3,370.9 $ 16.0 $ 6,366.6 $ 31.3 As of March 31, 2021, 991 debt securities available for sale with a combined fair value of $12.5 billion were in an unrealized loss position, with their unrealized losses totaling $257.7 million. Unrealized losses related to debt securities available for sale of $160.2 million and $52.5 million related to government-sponsored agency and obligations of states and political subdivisions, respectively, are primarily attributable to changes in market interest rates and credit spreads since their purchase. As of March 31, 2021, 17% of the corporate debt securities available for sale portfolio were backed by guarantees provided by U.S. and non-U.S. governmental entities. The remaining unrealized losses on Northern Trust’s debt securities available for sale portfolio as of March 31, 2021 are attributable to changes in overall market interest rates or credit spreads. As of March 31, 2021, Northern Trust did not intend to sell any debt securities available for sale in an unrealized loss position and it was more likely than not that Northern Trust would not be required to sell any such investment before the recovery of its amortized cost basis, which may be maturity. Debt securities available for sale 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 no provision for credit losses for corporate debt securities available for sale for the three months ended March 31, 2021, while there was a $0.2 million provision for the three months ended March 31, 2020. There was no allowance for credit losses for corporate debt securities available for sale as of March 31, 2021 and December 31, 2020, respectively. The process for identifying credit losses for corporate debt available for sale 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 7 — Allowance for Credit Losses. Debt Securities Held to Maturity. The following tables provide the amortized cost and fair values at March 31, 2021 and December 31, 2020, and remaining maturities of debt securities held to maturity at March 31, 2021. TABLE 37: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF DEBT SECURITIES HELD TO MATURITY MARCH 31, 2021 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR U.S Government $ 100.0 $ — $ — $ 100.0 Obligations of States and Political Subdivisions 1.0 — — 1.0 Government Sponsored Agency 53.6 0.3 0.9 53.0 Non-U.S. Government 6,539.3 6.1 0.2 6,545.2 Corporate Debt 916.7 5.0 1.6 920.1 Covered Bonds 3,046.8 19.9 1.7 3,065.0 Certificates of Deposit 644.1 — — 644.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 4,672.6 33.1 23.3 4,682.4 Other Asset-Backed 706.2 1.2 0.3 707.1 Other 456.1 1.0 75.0 382.1 Total $ 17,136.4 $ 66.6 $ 103.0 $ 17,100.0 DECEMBER 31, 2020 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR U.S. Government $ 90.0 $ — $ — $ 90.0 Obligations of States and Political Subdivisions 2.1 0.1 — 2.2 Government Sponsored Agency 3.0 0.3 — 3.3 Non-U.S. Government 8,336.6 7.3 0.2 8,343.7 Corporate Debt 588.0 6.5 0.1 594.4 Covered Bonds 3,184.6 24.6 0.3 3,208.9 Certificates of Deposit 807.2 — — 807.2 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,648.0 43.5 0.9 3,690.6 Other Asset-Backed 677.0 0.9 — 677.9 Other 454.6 1.1 76.5 379.2 Total $ 17,791.1 $ 84.3 $ 78.0 $ 17,797.4 As of March 31, 2021, the $17.1 billion debt securities held to maturity portfolio had an unrealized loss of $75 million related to other residential mortgage-backed securities and an unrealized loss of $23.3 million related to sub-sovereign, supranational and non-U.S. agency bonds, which are primarily attributable to changes in overall market interest rates and credit spreads since their purchase. TABLE 38: REMAINING MATURITY OF DEBT SECURITIES HELD TO MATURITY MARCH 31, 2021 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 $ 100.0 $ 100.0 $ — $ — $ — $ — $ — $ — $ 100.0 $ 100.0 Obligations of States and Political Subdivisions 1.0 1.0 — — — — — — 1.0 1.0 Government Sponsored Agency 2.0 2.0 8.0 8.0 9.2 9.2 34.4 33.8 53.6 53.0 Non-U.S. Government 6,049.0 6,049.1 490.3 496.1 — — — — 6,539.3 6,545.2 Corporate Debt 77.9 77.9 774.1 778.0 64.7 64.2 — — 916.7 920.1 Covered Bonds 1,294.1 1,300.2 1,431.9 1,445.1 320.8 319.7 — — 3,046.8 3,065.0 Certificates of Deposit 644.1 644.1 — — — — — — 644.1 644.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 1,206.4 1,212.0 2,334.3 2,358.2 1,131.9 1,112.2 — — 4,672.6 4,682.4 Other Asset-Backed 203.9 204.3 392.6 393.3 109.7 109.5 — — 706.2 707.1 Other 36.5 36.0 252.8 236.6 53.4 47.5 113.4 62.0 456.1 382.1 Total $ 9,614.9 $ 9,626.6 $ 5,684.0 $ 5,715.3 $ 1,689.7 $ 1,662.3 $ 147.8 $ 95.8 $ 17,136.4 $ 17,100.0 Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments. Debt securities held to maturity consist of securities that management intends to, and Northern Trust has the ability to, hold until maturity. During the three months ended March 31, 2021 and 2020, no securities were transferred from available for sale to held to maturity. Credit Quality Indicators. The following table provides the amortized cost of debt securities held to maturity by credit rating. TABLE 39: AMORTIZED COST OF DEBT SECURITIES HELD TO MATURITY BY CREDIT RATING AS OF MARCH 31, 2021 (In Millions) AAA AA A BBB NOT RATED TOTAL U.S. Government $ 100.0 $ — $ — $ — $ — $ 100.0 Obligations of States and Political Subdivisions — 1.0 — — — 1.0 Government Sponsored Agency 53.6 — — — — 53.6 Non-U.S. Government 301.0 205.1 5,760.4 272.8 — 6,539.3 Corporate Debt 75.1 396.0 445.6 — — 916.7 Covered Bonds 3,046.8 — — — — 3,046.8 Certificates of Deposit — — — — 644.1 644.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,301.2 1,339.8 31.6 — — 4,672.6 Other Asset-Backed 706.2 — — — — 706.2 Other — — — — 456.1 456.1 Total $ 7,583.9 $ 1,941.9 $ 6,237.6 $ 272.8 $ 1,100.2 $ 17,136.4 Percent of Total 44 % 11 % 36 % 2 % 7 % 100 % AS OF DECEMBER 31, 2020 (In Millions) AAA AA A BBB NOT RATED TOTAL U.S. Government $ 90.0 $ — $ — $ — $ — $ 90.0 Obligations of States and Political Subdivisions — 1.0 — 1.1 — 2.1 Government Sponsored Agency 3.0 — — — — 3.0 Non-U.S. Government 319.8 1,337.4 6,630.6 48.8 — 8,336.6 Corporate Debt 3.8 279.1 305.1 — — 588.0 Covered Bonds 3,184.6 — — — — 3,184.6 Certificates of Deposit — — — — 807.2 807.2 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,590.9 1,057.1 — — — 3,648.0 Other Asset-Backed 677.0 — — — — 677.0 Other — — — — 454.6 454.6 Total $ 6,869.1 $ 2,674.6 $ 6,935.7 $ 49.9 $ 1,261.8 $ 17,791.1 Percent of Total 39 % 15 % 39 % — % 7 % 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 91% and 93% of the held to maturity portfolio at March 31, 2021 and December 31, 2020, respectively, comprised of securities rated A or higher. The remaining held to maturity debt securities portfolio was comprised of 2% rated BBB at March 31, 2021 and 7% not rated by Moody’s Investors Service, Standard and Poor’s or Fitch Ratings at March 31, 2021 and December 31, 2020, respectively. Securities not explicitly rated were grouped where possible under the credit rating of the issuer of the security. Investment Security Gains and Losses. There were no sales of debt securities during the three months ended March 31, 2021. Proceeds of $280.0 million from the sale of debt securities during the three months ended March 31, 2020 resulted in gross realized debt securities gains of $0.7 million and gross realized debt securities losses of $0.7 million. There were no net investment security (losses) gains for the three months ended March 31, 2021 and 2020.

Securities Sold Under Agreement

Securities Sold Under Agreements to Repurchase	3 Months Ended
	Mar. 31, 2021
Banking and Thrift, Other Disclosures [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 held by the counterparty until the repurchase. The following table provides information regarding repurchase agreements that are accounted for as secured borrowings as of March 31, 2021 and December 31, 2020. TABLE 40: REPURCHASE AGREEMENTS ACCOUNTED FOR AS SECURED BORROWINGS REMAINING CONTRACTUAL MATURITY OF THE AGREEMENTS OVERNIGHT AND CONTINUOUS ($ In Millions) MARCH 31, 2021 DECEMBER 31, 2020 U.S. Treasury and Agency Securities $ 95.6 $ 39.8 Total Borrowings 95.6 39.8 Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 23 95.6 39.8 Amounts related to agreements not included in Note 23 — —

Loans and Leases

Loans and Leases	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Loans and Leases	Loans and Leases Amounts outstanding for Loans and Leases, by segment and class, are shown in the following table. TABLE 41: LOANS AND LEASES (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Commercial Commercial and Institutional $ 10,073.1 $ 10,058.3 Commercial Real Estate 3,713.9 3,558.4 Non-U.S. 1,771.2 1,345.7 Lease Financing, net 11.3 11.4 Other 278.4 288.2 Total Commercial 15,847.9 15,262.0 Personal Private Client 12,047.5 11,815.1 Residential Real Estate 6,066.9 6,035.7 Non-U.S. 336.7 597.9 Other 45.3 49.0 Total Personal 18,496.4 18,497.7 Total Loans and Leases $ 34,344.3 $ 33,759.7 Residential real estate loans consist of traditional first lien mortgages and equity credit lines that generally require a loan-to-collateral value of no more than 65% to 80% at inception. Northern Trust’s equity credit line products generally have draw periods of up to 10 years and a balloon payment of any outstanding balance is due at maturity. Payments are interest-only with variable interest rates. Northern Trust does not offer equity credit lines that include an option to convert the outstanding balance to an amortizing payment loan. As of March 31, 2021 and December 31, 2020, equity credit lines totaled $285.2 million and $304.4 million, respectively, and equity credit lines for which first liens were held by Northern Trust represented 97% of the total equity credit lines as of both March 31, 2021 and December 31, 2020. Included within the non-U.S., commercial-other and personal-other classes are short-duration advances primarily related to the processing of custodied client investments, totaling $1.3 billion at March 31, 2021 and $1.1 billion at December 31, 2020, respectively. Demand deposit overdrafts reclassified as loan balances totaled $5.6 million and $26.4 million at March 31, 2021 and December 31, 2020, respectively. As of March 31, 2021 and December 31, 2020, there were no loans or leases classified as held for sale. Paycheck Protection Program. In response to the COVID-19 pandemic, Northern Trust became a lender under the Paycheck Protection Program, as amended (PPP), which was created by the Coronavirus Aid, Relief, and Economic Security (CARES) Act and is administered by the U.S. Small Business Administration (SBA). Loans issued under the PPP are funded by Northern Trust directly to participating borrowers. The PPP loans are guaranteed by the SBA and borrowers are eligible to apply for PPP loan forgiveness for up to the full principal amount and accrued interest of the PPP loan. To the extent a borrower uses PPP loan proceeds to cover eligible costs and has met all other SBA loan forgiveness requirements, the SBA will determine loan forgiveness under the CARES Act and will pay to Northern Trust the eligible PPP loan forgiven amount, which will be credited to the borrower’s loan to repay or pay down the PPP loan. The SBA forgiveness portal opened on August 10, 2020 and Northern Trust’s vendor portal opened on September 11, 2020 to begin processing the PPP loan forgiveness applications. When Northern Trust submits forgiveness applications to the SBA, the SBA will have at least 90 days to respond as to the approval or denial of such application. 219 PPP loan forgiveness applications totaling $34.2 million that went through the forgiveness process as of March 31, 2021, were fully forgiven by the SBA as of such date. As of March 31, 2021, Northern Trust had 1,137 outstanding loans totaling $213.9 million under the PPP in its commercial and institutional portfolio with an average loan balance of $0.2 million. For its origination efforts, Northern Trust received approximately $2.6 million in SBA fees, net of service charges as of March 31, 2021. Northern Trust accounts for loans originated under the PPP as loan receivables in accordance with Accounting Standards Codification (ASC) 310 and recognizes such loans at the principal amount less the net amount of loan origination fees. PPP loans are reported in Total Loans and Leases on the consolidated balance sheets. The SBA provides a 100% guarantee on PPP loans covering principal and interest. Northern Trust considers the risk mitigating effects of these guarantees, and accounts for them as a credit enhancement embedded in the contract. As a result, no allowance for credit losses is measured for Northern Trust’s exposure under the PPP. Credit Quality Indicators. Credit quality indicators are statistics, measurements or other metrics that provide information regarding the relative credit risk of loans and leases. Northern Trust utilizes a variety of credit quality indicators to assess the credit risk of loans and leases 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 and leases 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 and lease 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; • Lease Financing and 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 and lease segment and class balances as of March 31, 2021 and December 31, 2020 are provided in the following table, segregated by borrower ratings into “1 to 3,” “4 to 5” and “6 to 9” (watch list and nonaccrual status) categories by year of origination at amortized cost basis. Loans that are held for investment are reported at the principal amount outstanding, net of unearned income. TABLE 42: CREDIT QUALITY INDICATOR AT AMORTIZED COST BASIS BY ORIGINATION YEAR March 31, 2021 TERM LOANS AND LEASES REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2021 2020 2019 2018 2017 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 334.2 $ 653.5 $ 332.8 $ 179.2 $ 103.4 $ 786.0 $ 3,597.0 $ 1.2 $ 5,987.3 4 to 5 Category 196.1 697.7 524.6 339.9 343.7 288.1 1,351.5 33.6 3,775.2 6 to 9 Category 29.9 33.4 77.9 36.7 39.5 24.9 68.3 — 310.6 Total Commercial and Institutional 560.2 1,384.6 935.3 555.8 486.6 1,099.0 5,016.8 34.8 10,073.1 Commercial Real Estate Risk Rating: 1 to 3 Category 124.7 341.5 153.4 59.8 24.3 113.5 82.6 2.8 902.6 4 to 5 Category 121.4 752.7 752.0 282.2 115.8 542.7 98.8 9.4 2,675.0 6 to 9 Category 12.1 18.2 55.2 15.5 23.9 11.4 — — 136.3 Total Commercial Real Estate 258.2 1,112.4 960.6 357.5 164.0 667.6 181.4 12.2 3,713.9 Non-U.S. Risk Rating: 1 to 3 Category 724.7 112.9 17.0 — 11.1 — 270.0 — 1,135.7 4 to 5 Category 282.1 28.0 0.7 2.1 — 85.2 129.5 1.8 529.4 6 to 9 Category 0.2 — 23.1 — — — 82.8 — 106.1 Total Non-U.S. 1,007.0 140.9 40.8 2.1 11.1 85.2 482.3 1.8 1,771.2 Lease Financing, net Risk Rating: 4 to 5 Category — — — — — 11.3 — — 11.3 Total Lease Financing, net — — — — — 11.3 — — 11.3 Other Risk Rating: 1 to 3 Category 135.8 — — — — — — — 135.8 4 to 5 Category 142.6 — — — — — — — 142.6 Total Other 278.4 — — — — — — — 278.4 Total Commercial 2,103.8 2,637.9 1,936.7 915.4 661.7 1,863.1 5,680.5 48.8 15,847.9 Personal Private Client Risk Rating: 1 to 3 Category 50.9 567.3 122.5 43.7 54.5 141.5 5,283.6 59.1 6,323.1 4 to 5 Category 229.2 535.5 595.7 115.1 64.2 100.0 3,805.1 210.6 5,655.4 6 to 9 Category 0.1 5.8 0.5 21.7 — — 39.6 1.3 69.0 Total Private Client 280.2 1,108.6 718.7 180.5 118.7 241.5 9,128.3 271.0 12,047.5 Residential Real Estate Risk Rating: 1 to 3 Category 375.1 1,440.3 247.7 25.3 99.1 771.4 143.7 — 3,102.6 4 to 5 Category 150.7 877.9 359.8 111.0 127.5 957.6 245.4 5.6 2,835.5 6 to 9 Category 0.3 14.1 8.1 0.6 0.5 82.6 22.6 — 128.8 Total Residential Real Estate 526.1 2,332.3 615.6 136.9 227.1 1,811.6 411.7 5.6 6,066.9 Non-U.S. Risk Rating: 1 to 3 Category — 9.2 32.3 — — 1.1 65.9 — 108.5 4 to 5 Category — 10.2 8.2 10.7 0.4 8.8 176.0 13.6 227.9 6 to 9 Category — — — — — 0.3 — — 0.3 Total Non-U.S. — 19.4 40.5 10.7 0.4 10.2 241.9 13.6 336.7 Other Risk Rating: 1 to 3 Category 26.8 — — — — — — — 26.8 4 to 5 Category 18.5 — — — — — — — 18.5 Total Other 45.3 — — — — — — — 45.3 Total Personal 851.6 3,460.3 1,374.8 328.1 346.2 2,063.3 9,781.9 290.2 18,496.4 Total Loans and Leases $ 2,955.4 $ 6,098.2 $ 3,311.5 $ 1,243.5 $ 1,007.9 $ 3,926.4 $ 15,462.4 $ 339.0 $ 34,344.3 December 31, 2020 TERM LOANS AND LEASES REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2020 2019 2018 2017 2016 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 663.8 $ 546.0 $ 204.6 $ 96.0 $ 396.0 $ 448.8 $ 3,742.4 $ 5.5 $ 6,103.1 4 to 5 Category 793.4 505.1 354.1 405.4 134.6 167.3 1,238.7 32.3 3,630.9 6 to 9 Category 34.3 119.8 37.3 42.8 23.0 6.0 61.1 — 324.3 Total Commercial and Institutional 1,491.5 1,170.9 596.0 544.2 553.6 622.1 5,042.2 37.8 10,058.3 Commercial Real Estate Risk Rating: 1 to 3 Category 406.3 109.2 27.6 36.5 11.8 99.4 124.3 8.7 823.8 4 to 5 Category 703.1 811.8 332.7 107.4 184.5 382.8 60.4 11.4 2,594.1 6 to 9 Category 15.3 55.2 32.0 25.8 — 12.2 — — 140.5 Total Commercial Real Estate 1,124.7 976.2 392.3 169.7 196.3 494.4 184.7 20.1 3,558.4 Non-U.S. Risk Rating: 1 to 3 Category 555.2 16.8 — 11.1 — — 78.5 — 661.6 4 to 5 Category 313.1 0.7 2.0 — — 157.9 39.2 1.8 514.7 6 to 9 Category — 23.1 — — — — 146.3 — 169.4 Total Non-U.S. 868.3 40.6 2.0 11.1 — 157.9 264.0 1.8 1,345.7 Lease Financing, net Risk Rating: 4 to 5 Category — — — — — 11.4 — — 11.4 Total Lease Financing, net — — — — — 11.4 — — 11.4 Other Risk Rating: 1 to 3 Category 81.7 — — — — — — — 81.7 4 to 5 Category 206.5 — — — — — — — 206.5 Total Other 288.2 — — — — — — — 288.2 Total Commercial 3,772.7 2,187.7 990.3 725.0 749.9 1,285.8 5,490.9 59.7 15,262.0 Personal Private Client Risk Rating: 1 to 3 Category 668.6 273.7 51.7 60.4 10.2 136.1 5,392.8 47.9 6,641.4 4 to 5 Category 492.1 479.9 117.3 60.4 77.5 77.5 3,564.7 207.3 5,076.7 6 to 9 Category 6.0 0.5 22.1 3.2 — — 63.7 1.5 97.0 Total Private Client 1,166.7 754.1 191.1 124.0 87.7 213.6 9,021.2 256.7 11,815.1 Residential Real Estate Risk Rating: 1 to 3 Category 1,554.3 317.4 42.9 109.9 205.1 627.8 152.8 1.7 3,011.9 4 to 5 Category 854.6 359.5 115.8 163.2 209.7 896.5 273.1 7.4 2,879.8 6 to 9 Category 15.3 8.3 0.7 0.5 1.9 94.8 22.5 — 144.0 Total Residential Real Estate 2,424.2 685.2 159.4 273.6 416.7 1,619.1 448.4 9.1 6,035.7 Non-U.S. Risk Rating: 1 to 3 Category 23.3 14.9 — — — 1.8 275.6 — 315.6 4 to 5 Category 12.7 26.0 11.8 0.5 0.5 7.9 217.5 5.1 282.0 6 to 9 Category — — — — — 0.3 — — 0.3 Total Non-U.S. 36.0 40.9 11.8 0.5 0.5 10.0 493.1 5.1 597.9 Other Risk Rating: 1 to 3 Category 34.6 — — — — — — — 34.6 4 to 5 Category 14.4 — — — — — — — 14.4 Total Other 49.0 — — — — — — — 49.0 Total Personal 3,675.9 1,480.2 362.3 398.1 504.9 1,842.7 9,962.7 270.9 18,497.7 Total Loans and Leases $ 7,448.6 $ 3,667.9 $ 1,352.6 $ 1,123.1 $ 1,254.8 $ 3,128.5 $ 15,453.6 $ 330.6 $ 33,759.7 Loans and leases 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 and leases 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 and leases 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 minimally acceptable 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 and leases 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 and leases by segment and class, as well as the other real estate owned and nonaccrual asset balances, as of March 31, 2021 and December 31, 2020. TABLE 43: DELINQUENCY STATUS ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS March 31, 2021 Commercial Commercial and Institutional $ 10,024.5 $ 25.1 $ 2.2 $ — $ 10,051.8 $ 21.3 $ 10,073.1 $ 9.9 Commercial Real Estate 3,660.5 8.7 — 4.6 3,673.8 40.1 3,713.9 32.2 Non-U.S. 1,771.2 — — — 1,771.2 — 1,771.2 — Lease Financing, net 11.3 — — — 11.3 — 11.3 — Other 278.4 — — — 278.4 — 278.4 — Total Commercial 15,745.9 33.8 2.2 4.6 15,786.5 61.4 15,847.9 42.1 Personal Private Client 11,912.3 103.4 11.1 17.8 12,044.6 2.9 12,047.5 2.9 Residential Real Estate 5,976.1 28.0 1.7 1.6 6,007.4 59.5 6,066.9 51.1 Non-U.S. 336.5 0.2 — — 336.7 — 336.7 — Other 45.3 — — — 45.3 — 45.3 — Total Personal 18,270.2 131.6 12.8 19.4 18,434.0 62.4 18,496.4 54.0 Total Loans and Leases $ 34,016.1 $ 165.4 $ 15.0 $ 24.0 $ 34,220.5 $ 123.8 $ 34,344.3 $ 96.1 Other Real Estate Owned $ 1.5 Total Nonaccrual Assets $ 125.3 ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS December 31, 2020 Commercial Commercial and Institutional $ 9,877.0 $ 153.7 $ 1.2 $ — $ 10,031.9 $ 26.4 $ 10,058.3 $ 9.1 Commercial Real Estate 3,516.2 2.0 — — 3,518.2 40.2 3,558.4 32.3 Non-U.S. 1,345.7 — — — 1,345.7 — 1,345.7 — Lease Financing, net 11.4 — — — 11.4 — 11.4 — Other 288.2 — — — 288.2 — 288.2 — Total Commercial 15,038.5 155.7 1.2 — 15,195.4 66.6 15,262.0 41.4 Personal Private Client 11,765.4 29.1 9.9 7.8 11,812.2 2.9 11,815.1 2.9 Residential Real Estate 5,946.0 23.5 2.9 1.1 5,973.5 62.2 6,035.7 53.8 Non-U.S 596.7 1.2 — — 597.9 — 597.9 — Other 49.0 — — — 49.0 — 49.0 — Total Personal 18,357.1 53.8 12.8 8.9 18,432.6 65.1 18,497.7 56.7 Total Loans and Leases $ 33,395.6 $ 209.5 $ 14.0 $ 8.9 $ 33,628.0 $ 131.7 $ 33,759.7 $ 98.1 Other Real Estate Owned $ 0.7 Total Nonaccrual Assets $ 132.4 Interest income that would have been recorded for nonaccrual loans and leases in accordance with their original terms was $0.9 million and $1.3 million for the three months ended March 31, 2021 and March 31, 2020, respectively. Collateral Dependent Financial Assets. A financial asset is collateral-dependent when the borrower is experiencing financial difficulty and repayment is expected to be provided substantially through the sale or operation of the collateral. Most of Northern Trust’s collateral dependent credit exposure relates to its residential real estate portfolio for which the collateral is usually the underlying real estate property. For collateral dependent financial assets, it is Northern Trust’s policy to reserve or charge-off the difference between the amortized cost basis of the loan and the value of the collateral. The collateral dependent financial asset balance as of March 31, 2021 was immaterial to Northern Trust’s financial statements. Recognition of Income. Interest income on loans and leases is recorded on an accrual basis unless, in the opinion of management, there is a question as to the ability of the debtor to meet the terms of the loan agreement, or interest or principal is more than 90 days contractually past due and the loan is not well-secured and in the process of collection. Loans meeting such criteria are classified as nonaccrual and interest income is recorded on a cash basis. At the time a loan is determined to be nonaccrual, interest accrued but not collected is reversed against interest income in the current period. Interest collected on nonaccrual loans is applied to principal unless, in the opinion of management, collectability of principal is not in doubt. Management’s assessment of the indicators of loan and lease collectability, and its policies relative to the recognition of interest income, including the suspension and subsequent resumption of income recognition, do not meaningfully vary between loan and lease classes. Nonaccrual loans are returned to accrual status when factors indicating doubtful collectability no longer exist. Factors considered in returning a loan to accrual status are consistent across all classes of loans and leases and, in accordance with regulatory guidance, relate primarily to expected payment performance. Loans are eligible to be returned to accrual status when: (i) no principal or interest that is due is unpaid and repayment of the remaining contractual principal and interest is expected or (ii) the loan has otherwise become well-secured (possessing realizable value sufficient to discharge the debt, including accrued interest, in full) and is in the process of collection (through action reasonably expected to result in debt repayment or restoration to a current status in the near future). A loan that has not been brought fully current may be restored to accrual status provided there has been a sustained period of repayment performance (generally a minimum of six payment periods) by the borrower in accordance with the contractual terms, and Northern Trust is reasonably assured of repayment within a reasonable period of time. Additionally, a loan that has been formally restructured so as to be reasonably assured of repayment and performance according to its modified terms may be returned to accrual status, provided there was a well-documented credit evaluation of the borrower’s financial condition and prospects of repayment under the revised terms and there has been a sustained period of repayment performance (generally a minimum of six payment periods) under the revised terms. Nonaccrual Loans and Troubled Debt Restructurings (TDRs). 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 and leases. All loans and leases 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 $78.8 million and $38.9 million of nonaccrual TDRs, and $23.3 million and $29.3 million of accrual TDRs as of March 31, 2021 and December 31, 2020, respectively. There were $8.9 million and $10.4 million of aggregate undrawn loan commitments and standby letters of credit at March 31, 2021 and December 31, 2020, respectively, issued to borrowers with TDR modifications of loans. The following table provides, by segment and class, the number of TDR modifications of loans and leases during the three month periods ended March 31, 2021 and 2020, and the recorded investments and unpaid principal balances as of March 31, 2021 and 2020. TABLE 44: TROUBLED DEBT RESTRUCTURINGS THREE MONTHS ENDED MARCH 31, 2021 ($ In Millions) NUMBER OF RECORDED UNPAID Commercial Commercial and Institutional 6 $ 19.6 $ 19.6 Commercial Real Estate 1 21.4 23.3 Total Commercial 7 41.0 42.9 Personal Residential Real Estate 2 0.2 0.3 Total Personal 2 0.2 0.3 Total Loans and Leases 9 $ 41.2 $ 43.2 Note: Period-end balances reflect all paydowns and charge-offs during the period. THREE MONTHS ENDED MARCH 31, 2020 ($ In Millions) NUMBER OF RECORDED UNPAID Commercial Commercial and Institutional 2 $ 24.3 $ 24.5 Total Commercial 2 24.3 24.5 Personal Residential Real Estate 6 1.0 1.2 Total Personal 6 1.0 1.2 Total Loans and Leases 8 $ 25.3 $ 25.7 Note: Period-end balances reflect all paydowns and charge-offs during the period. 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. During the three months ended March 31, 2021, the TDR modification of loans within commercial and institutional, residential real estate and commercial real estate was deferred principal. During the three months ended March 31, 2020, the TDR modifications of loans within residential real estate were extensions of term, other modifications, interest rate concessions, and deferred principal. During the three months ended March 31, 2020, the TDR modifications within commercial and institutional were other modifications. There was one residential real estate loan TDR modification during the twelve months ended December 31, 2020, which subsequently had a payment default during the three months ended March 31, 2021. The total recorded investment for this loan was approximately $5.5 million and the unpaid principal balance for these loans was approximately $5.5 million. There were no residential real estate loan TDR modifications during the twelve months ended December 31, 2019, which subsequently had a payment default during the three months ended March 31, 2020. Northern Trust may obtain physical possession of real estate via foreclosure on an in-substance repossession. As of March 31, 2021, Northern Trust held foreclosed real estate properties with a carrying value of $1.5 million as a result of obtaining physical possession. In addition, as of March 31, 2021, Northern Trust had loans with a carrying value of $6.5 million for which formal foreclosure proceedings were in process. TDR Relief — COVID-19. Due to the economic environment arising from the COVID-19 pandemic, there have been two forms of relief provided for classifying loans as TDRs: the Interagency Guidance (as defined below) and the CARES Act. Various banking regulators, including the Board of Governors of the Federal Reserve System, the Federal Deposit Insurance Corporation, the National Credit Union Administration, the Office of the Comptroller of the Currency, and the Consumer Financial Protection Bureau, issued guidance in the April 7, 2020 Interagency Statement on Loan Modifications and Reporting for Financial Institutions Working with Customers Affected by the Coronavirus (revised) on loan modification treatment (Interagency Guidance) pursuant to which financial institutions can apply ASC 310-40 Receivables – Troubled Debt Restructurings by Creditors. In accordance with the Interagency Guidance, a loan modification is not considered a TDR if the modification is related to COVID-19; the borrower had been current (not more than 29 days past due) when the modification program was implemented; and the modification includes payment deferrals for not more than 6 months. Under section 4013 of the CARES Act, relief provided to lenders exempting certain loan modifications which would otherwise be classified as TDRs from such classification applies for loans that were not more than 30 days past due as of December 31, 2019. The TDR relief under the CARES Act applies to COVID-19-related modifications that were made from March 1, 2020 until the earlier of (a) January 1, 2022 or (b) 60 days from the date the COVID-19 national emergency officially ends. Financial institutions may account for eligible loan modifications under the Interagency Guidance and/or the CARES Act. Northern Trust elected to apply both the CARES Act and the Interagency Guidance, as applicable, in providing borrowers with loan modification relief in response to the COVID-19 pandemic. All other types of modifications which do not meet the CARES Act or Interagency Guidance requirements continue to be governed by existing regulations and accounting policies. The following tables provide, by segment and class, the number of total COVID-19-related loan modifications including the loan volume and deferred principal and interest balances as of March 31, 2021, for which Northern Trust applied an exemption from TDR classification that are in active deferral (loans currently in the deferral period) or completed deferral (loans that returned to their regular payment schedule). TABLE 45: COVID-19 LOAN MODIFICATIONS NOT CONSIDERED TDRS IN ACTIVE DEFERRAL STATUS MARCH 31, 2021 ($ In Millions) NUMBER OF COVID-19 RELATED MODIFICATIONS LOAN VOLUME DEFERRED PRINCIPAL AMOUNT DEFERRED INTEREST AMOUNT Personal Residential Real Estate 25 $ 9.5 $ 0.2 $ 0.2 Total Personal 25 $ 9.5 $ 0.2 $ 0.2 Total Loans 25 $ 9.5 $ 0.2 $ 0.2 TABLE 46: COVID-19 LOAN MODIFICATIONS NOT CONSIDERED TDRS THAT HAVE COMPLETED DEFERRAL MARCH 31, 2021 ($ In Millions) NUMBER OF COVID-19 RELATED MODIFICATIONS LOAN VOLUME DEFERRED PRINCIPAL AMOUNT DEFERRED INTEREST AMOUNT Commercial Commercial and Institutional 90 $ 238.4 $ — $ 2.0 Commercial Real Estate 91 457.2 — 3.2 Total Commercial 181 $ 695.6 $ — $ 5.2 Personal Private Client 32 $ 169.8 $ — $ 1.2 Residential Real Estate 382 164.8 1.4 2.0 Total Personal 414 $ 334.6 $ 1.4 $ 3.2 Total Loans 595 $ 1,030.2 $ 1.4 $ 8.4 Northern Trust continues to accrue and recognize interest income during the loan deferral period, and hence has not moved these loans to nonaccrual or reported them as past due. Further, these loan balances continue to be assessed on a collective basis for purposes of measuring an allowance for expected credit losses. During the three months ended March 31, 2021, 38 loans with an aggregate principal amount of $42.9 million that had been granted payment deferrals were paid off.

Allowance for Credit Losses

Allowance for Credit Losses	3 Months Ended
	Mar. 31, 2021
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 group, and each of Northern Trust’s business units. The Credit Loss Reserve Committee determines the probability weights applied to each forecast approved by Northern Trust’s Macroeconomic Scenario Development Committee, and also reviews and approves qualitative adjustments to the collective allowance in line with Northern Trust’s qualitative adjustment framework. The following table provides information regarding changes in the total allowance for credit losses during the three months ended March 31, 2021 and 2020. TABLE 47: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES THREE MONTHS ENDED MARCH 31, 2021 (In Millions) LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT DEBT SECURITIES HELD TO MATURITY OTHER FINANCIAL ASSETS TOTAL Balance at Beginning of Period $ 190.7 $ 61.1 $ 7.3 $ 0.8 $ 259.9 Charge-Offs (0.4) — — — (0.4) Recoveries 1.3 — — — 1.3 Net Recoveries (Charge-Offs) 0.9 — — — 0.9 Provision for Credit Losses (26.2) (6.0) 1.3 0.9 (30.0) Balance at End of Period $ 165.4 $ 55.1 $ 8.6 $ 1.7 $ 230.8 THREE MONTHS ENDED MARCH 31, 2020 (In Millions) LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT DEBT SECURITIES HELD TO MATURITY OTHER FINANCIAL ASSETS TOTAL Balance at End of Prior Period $ 104.5 $ 19.9 $ — $ — $ 124.4 Cumulative Effect Adjustment (2.2) 8.9 6.6 0.4 13.7 Balance at Beginning of Period $ 102.3 $ 28.8 $ 6.6 $ 0.4 $ 138.1 Charge-Offs (1.8) — — — (1.8) Recoveries 1.1 — — — 1.1 Net Recoveries (Charge-Offs) (0.7) — — — (0.7) Provision for Credit Losses (1) 45.6 11.6 2.9 0.7 60.8 Balance at End of Period $ 147.2 $ 40.4 $ 9.5 $ 1.1 $ 198.2 (1) The table excludes $0.2 million of credit losses recognized for corporate debt securities available for sale as of March 31, 2020. See further detail in Note 4 - Securities. The portion of the allowance assigned to loans and leases, debt securities held to maturity, 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 14 — Revenue from Contracts with Clients. For information related to the allowance for debt securities available for sale, 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, Federal Funds Sold, and Other Assets, please refer to the Allowance for Other Financial Assets section within this footnote. 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 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 than or less than actual net charge-offs. There was a $30.0 million release of credit reserves in the current quarter, as compared to a $61.0 million provision in the prior-year quarter. There were net recoveries of $0.9 million during the three months ended March 31, 2021, as compared to net charge-offs of $0.7 million for the three months ended March 31, 2020. The release of credit reserves in the current quarter was primarily due to a decrease in the reserve evaluated on a collective basis, which relates to pooled financial assets sharing similar risk characteristics. The decrease in the collective basis reserve was driven by continued improvement in projected economic conditions and portfolio credit quality relative to the prior quarter, with decreases primarily in the commercial and institutional, commercial real estate, and private client portfolios. 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. Management determines the probability weights assigned to each scenario at each quarter-end. 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. For the current quarter, the primary forecast, consistent with Northern Trust’s economic outlook publications, assumes continued economic recovery from the challenges of COVID-19, with strong growth and a falling unemployment rate over the forecast horizon. An alternative scenario is also considered, which contemplates a resurgence of the virus, causing a double-dip recession. 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 and Lease Portfolio. The following table provides information regarding changes in the total allowance for credit losses, including undrawn loan commitments and standby letters of credit, by segment during the three months ended March 31, 2021 and 2020. TABLE 48: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO LOANS AND LEASES THREE MONTHS ENDED MARCH 31, 2021 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 142.2 $ 48.5 $ 190.7 $ 57.6 $ 3.5 $ 61.1 Charge-Offs — (0.4) (0.4) — — — Recoveries — 1.3 1.3 — — — Net Recoveries (Charge-Offs) — 0.9 0.9 — — — Provision for Credit Losses (17.5) (8.7) (26.2) (5.9) (0.1) (6.0) Balance at End of Period $ 124.7 $ 40.7 $ 165.4 $ 51.7 $ 3.4 $ 55.1 THREE MONTHS ENDED MARCH 31, 2020 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at End of Prior Period $ 58.1 $ 46.4 $ 104.5 $ 15.8 $ 4.1 $ 19.9 Cumulative Effect Adjustment (5.9) 3.7 (2.2) 11.9 (3.0) 8.9 Balance at Beginning of Period $ 52.2 $ 50.1 $ 102.3 $ 27.7 $ 1.1 $ 28.8 Charge-Offs (0.1) (1.7) (1.8) — — — Recoveries 0.7 0.4 1.1 — — — Net Recoveries (Charge-Offs) 0.6 (1.3) (0.7) — — — Provision for Credit Losses 41.9 3.7 45.6 11.1 0.5 11.6 Balance at End of Period $ 94.7 $ 52.5 $ 147.2 $ 38.8 $ 1.6 $ 40.4 The decrease to the allowance for both loans and leases and the allowance for undrawn loan commitments and standby letters of credit for the three months ended March 31, 2021 was primarily due to a decrease in the reserve evaluated on a collective basis, which relates to pooled financial assets sharing similar risk characteristics. The decrease in the collective basis reserve was driven by continued improvement in projected economic conditions and portfolio credit quality relative to the prior quarter, with decreases primarily in the commercial and institutional, commercial real estate, and private client portfolios. 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 and lease 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 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, leases, and lending-related commitments considered impaired 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 impaired 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 leases and the allowance for credit losses for loans and leases and undrawn loan commitments and standby letters of credit by segment as of March 31, 2021 and December 31, 2020. TABLE 49: RECORDED INVESTMENTS IN LOANS AND LEASES MARCH 31, 2021 DECEMBER 31, 2020 (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Loans and Leases Evaluated on an Individual Basis $ 61.4 $ 62.4 $ 123.8 $ 66.6 $ 65.1 $ 131.7 Evaluated on a Collective Basis 15,786.5 18,434.0 34,220.5 15,195.4 18,432.6 33,628.0 Total Loans and Leases 15,847.9 18,496.4 34,344.3 15,262.0 18,497.7 33,759.7 Allowance for Credit Losses on Credit Exposures Evaluated on an Individual Basis 10.6 0.3 10.9 8.8 0.3 9.1 Evaluated on a Collective Basis 114.1 40.4 154.5 133.4 48.2 181.6 Allowance Assigned to Loans and Leases 124.7 40.7 165.4 142.2 48.5 190.7 Allowance for Undrawn Loan Commitments and Standby Letters of Credit Evaluated on an Individual Basis — — — 1.6 — 1.6 Evaluated on a Collective Basis 51.7 3.4 55.1 56.0 3.5 59.5 Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit 51.7 3.4 55.1 57.6 3.5 61.1 Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit $ 176.4 $ 44.1 $ 220.5 $ 199.8 $ 52.0 $ 251.8 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 Debt Securities Held to Maturity Securities Portfolio. The following table provides information regarding changes in the total allowance for credit losses for debt securities held to maturity during the three months ended March 31, 2021 and March 31, 2020. TABLE 50: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO DEBT SECURITIES HELD TO MATURITY THREE MONTHS ENDED MARCH 31, 2021 (In Millions) CORPORATE DEBT NON-U.S. GOVERNMENT SUB-SOVEREIGN, SUPERNATIONAL, AND NON-U.S. AGENCY BONDS CERTIFICATE OF DEPOSITS COVERED BONDS OTHER TOTAL Balance at Beginning of Period $ 0.8 $ 0.2 $ 1.2 $ — $ 0.1 $ 5.0 $ 7.3 Provision for Credit Losses 0.3 0.7 0.6 — — (0.3) 1.3 Balance at End of Period $ 1.1 $ 0.9 $ 1.8 $ — $ 0.1 $ 4.7 $ 8.6 THREE MONTHS ENDED MARCH 31, 2020 (In Millions) CORPORATE DEBT NON-U.S. GOVERNMENT SUB-SOVEREIGN, SUPERNATIONAL, AND NON-U.S. AGENCY BONDS CERTIFICATE OF DEPOSITS COVERED BONDS OTHER TOTAL Balance at End of Prior Period $ — $ — $ — $ — $ — $ — $ — Cumulative Effect Adjustment 0.8 0.3 0.9 — — 4.6 6.6 Balance at Beginning of Period 0.8 0.3 0.9 — — 4.6 6.6 Provision for Credit Losses 1.9 0.1 0.4 0.2 0.1 0.2 2.9 Balance at End of Period $ 2.7 $ 0.4 $ 1.3 $ 0.2 $ 0.1 $ 4.8 $ 9.5 Debt securities held to maturity 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. Debt securities held to maturity classified as other asset-backed represent pools of underlying receivables from which the cash flows are used to pay the bonds that vary in seniority. Utilizing a qualitative estimation approach, the allowance for other asset-backed securities is assessed by evaluating underlying pool performance based on delinquency rates and available credit support. Debt securities held to maturity classified as other relates 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 debt securities held to maturity 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 Cash and Due from Banks, Other Central Bank Deposits, Interest Bearing Deposits with Banks, Federal Funds Sold, 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 used for the Debt Securities Held to Maturity portfolio. It consists of a combination of externally and internally developed loss data, adjusted for the appropriate contractual term. Northern Trust’s portfolio 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 $1.7 million and $0.8 million as of March 31, 2021 and December 31, 2020, 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 51: ACCRUED INTEREST (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Loans and Leases $ 59.4 $ 55.3 Debt Securities Held to Maturity $ 19.8 $ 26.5 Available for Sale 136.1 153.6 Other Financial Assets $ 1.6 $ 1.4 The amount of accrued interest reversed through interest income for loans and leases was immaterial and there was no accrued interest reversed through interest income related to any other financial assets for the three months ended March 31, 2021 and 2020.

Pledged and Restricted Assets

Pledged and Restricted Assets	3 Months Ended
	Mar. 31, 2021
Transfers and Servicing [Abstract]
Pledged and Restricted Assets	Pledged and Restricted Assets Certain of Northern Trust’s subsidiaries, as required or permitted by law, pledge assets to secure public and trust deposits, repurchase agreements and borrowings, as well as for other purposes, including support for securities settlement, primarily related to client activities, and for derivative contracts. The following table presents Northern Trust's pledged assets. TABLE 52: TYPE OF PLEDGED ASSETS (In Billions) MARCH 31, 2021 DECEMBER 31, 2020 Securities Obligations of States and Political Subdivisions $ 3.0 $ 2.9 Government Sponsored Agency and Other Securities 30.6 32.5 Loans 12.3 12.1 Total Pledged Assets $ 45.9 $ 47.5 Collateral required for these purposes totaled $1.6 billion and $5.7 billion at March 31, 2021 and December 31, 2020, respectively. The following table presents the available for sale debt securities pledged as collateral that are included in pledged assets. TABLE 53: FAIR VALUE OF AVAILABLE FOR SALE DEBT SECURITIES INCLUDED IN PLEDGED ASSETS SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE DERIVATIVE CONTRACTS (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 MARCH 31, 2021 DECEMBER 31, 2020 Debt Securities Available for Sale $ 93.0 $ 33.0 $ 29.3 $ 27.1 The secured parties to these transactions have the right to repledge or sell the securities as it relates to $93.4 million and $33.5 million of the pledged collateral as of March 31, 2021 and December 31, 2020, respectively. 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. There was no repledged or sold collateral at March 31, 2021 or December 31, 2020. TABLE 54: ACCEPTED COLLATERAL (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Collateral that may be repledged or sold Reverse repurchase agreements $ 309.3 $ 1,179.8 Derivative contracts 8.4 0.9 Collateral that may not be repledged or sold Reverse repurchase agreements 800.0 500.0 As a result of the economic environment arising from the COVID-19 pandemic, the Federal Reserve reduced the reserve requirement to zero percent on March 26, 2020. Deposits maintained to meet Federal Reserve Bank reserve requirements averaged $1.7 billion for the three months ended March 31, 2020.

Goodwill and Other Intangibles

Goodwill and Other Intangibles	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangibles	Goodwill and Other Intangibles Goodwill. Changes by reporting segment in the carrying amount of Goodwill for the three months ended March 31, 2021, including the effect of foreign exchange rates on non-U.S. dollar denominated balances, were as follows. TABLE 55: GOODWILL (In Millions) CORPORATE & INSTITUTIONAL SERVICES WEALTH MANAGEMENT TOTAL Balance at December 31, 2020 $ 636.0 $ 71.2 $ 707.2 Foreign Exchange Rates (3.2) — (3.2) Balance at March 31, 2021 $ 632.8 $ 71.2 $ 704.0 Other Intangible Assets Subject to Amortization . The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of March 31, 2021 and December 31, 2020 were as follows. TABLE 56: OTHER INTANGIBLE ASSETS (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Gross Carrying Amount $ 210.0 $ 221.3 Less: Accumulated Amortization 106.2 108.7 Net Book Value $ 103.8 $ 112.6 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 $4.3 million for the three months ended March 31, 2021, and $4.1 million for the three months ended March 31, 2020. Amortization for the remainder of 2021 and for the years 2022, 2023, 2024, and 2025 is estimated to be $10.5 million, $10.1 million, $9.8 million, $9.7 million, and $9.1 million, respectively. Capitalized Software. The gross carrying amount and accumulated amortization of capitalized software as of March 31, 2021 and December 31, 2020 were as follows. TABLE 57: CAPITALIZED SOFTWARE (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Gross Carrying Amount $ 4,404.8 $ 4,337.4 Less: Accumulated Amortization 2,810.5 2,744.5 Net Book Value $ 1,594.3 $ 1,592.9

Reporting Segments

Reporting Segments	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Reporting Segments	Reporting Segments Northern Trust is organized around its two client-focused reporting segments: Corporate & Institutional Services (C&IS) and Wealth Management. Asset management and related services are provided to C&IS 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 C&IS 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. Revenues, expenses and average assets are allocated to C&IS 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. Effective January 1, 2021, Northern Trust implemented enhancements to its FTP methodology, including enhancements impacting the allocation of net interest income between C&IS and Wealth Management. These methodology enhancements affect the results of each of these reporting segments. Due to the lack of historical information, segment results for periods ended prior to January 1, 2021 have not been revised to reflect the methodology enhancements. The following table presents the earnings contributions and average assets of Northern Trust’s reporting segments for the three month periods ended March 31, 2021 and 2020. TABLE 58: RESULTS OF REPORTING SEGMENTS ($ In Millions) CORPORATE & WEALTH MANAGEMENT OTHER TOTAL CONSOLIDATED THREE MONTHS ENDED MARCH 31, 2021 2020 2021 2020 2021 2020 2021 2020 Noninterest Income Trust, Investment and Other Servicing Fees $ 620.5 $ 574.4 $ 443.2 $ 429.2 $ — $ — $ 1,063.7 $ 1,003.6 Foreign Exchange Trading Income 74.5 85.1 4.2 3.8 — — 78.7 88.9 Other Noninterest Income 60.3 41.8 44.2 42.4 (3.6) 2.9 100.9 87.1 Total Noninterest Income 755.3 701.3 491.6 475.4 (3.6) 2.9 1,243.3 1,179.6 Net Interest Income (1) 160.7 211.3 186.0 204.9 — — 346.7 416.2 Revenue (1) 916.0 912.6 677.6 680.3 (3.6) 2.9 1,590.0 1,595.8 Provision for Credit Losses (5.4) 25.7 (24.6) 35.3 — — (30.0) 61.0 Noninterest Expense 713.1 659.3 403.1 394.4 1.3 11.9 1,117.5 1,065.6 Income before Income Taxes (1) 208.3 227.6 299.1 250.6 (4.9) (9.0) 502.5 469.2 Provision for Income Taxes (1) 50.1 49.9 78.5 60.9 (1.2) (2.2) 127.4 108.6 Net Income $ 158.2 $ 177.7 $ 220.6 $ 189.7 $ (3.7) $ (6.8) $ 375.1 $ 360.6 Percentage of Consolidated Net Income 42 % 49 % 59 % 53 % (1) % (2) % 100 % 100 % Average Assets $ 120,157.7 $ 92,715.3 $ 33,098.1 $ 31,455.2 $ — $ — $ 153,255.8 $ 124,170.5 (1) Non-GAAP financial measures stated on a fully taxable equivalent basis (FTE). Total consolidated includes FTE adjustments of $6.6 million for 2021 and $8.1 million for 2020.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock. The Corporation is authorized to issue 10 million shares of preferred stock without par value. The Board of Directors is authorized to fix the particular designations, preferences and relative, participating, optional and other special rights and qualifications, limitations or restrictions for each series of preferred stock issued. As of March 31, 2021, 5,000 shares of Series D Non-Cumulative Perpetual Preferred Stock (the “Series D Preferred Stock”) and 16,000 shares of Series E Non-Cumulative Perpetual Preferred Stock (“Series E Preferred Stock”) were outstanding. Series D Preferred Stock. As of March 31, 2021, the Corporation had issued and outstanding 500,000 depositary shares, each representing a 1/100th ownership interest in a share of Series D Preferred Stock, issued in August 2016. Equity related to Series D Preferred Stock as of March 31, 2021 and December 31, 2020 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 Three-Month LIBOR plus 3.202% from and including October 1, 2026. Fixed rate dividends are payable in arrears on the first day of April and October of each year, through and including October 1, 2026, and floating rate dividends will be payable in arrears on the first day of January, April, July and October of each year, commencing on January 1, 2027. On January 20, 2021, the Corporation declared a cash dividend of $2,300 per share of Series D Preferred Stock payable on April 1, 2021, to stockholders of record as of March 15, 2021. Series E Preferred Stock. As of March 31, 2021, the Corporation had issued and outstanding 16 million depositary shares, each representing 1/1,000th ownership interest in a share of Series E Preferred Stock, issued in November 2019. Equity related to Series E Preferred Stock as of March 31, 2021 and December 31, 2020 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, commencing on April 1, 2020, at a rate per annum equal to 4.70%. On January 20, 2021, the Corporation declared cash dividends of $293.75 per share of Series E Preferred Stock payable on April 1, 2021, to stockholders of record as of March 15, 2021. Common Stock. In July 2018, the Board of Directors approved a stock repurchase authorization to repurchase up to 25.0 million shares of the Corporation’s common stock. 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.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) The following tables summarize the components of Accumulated Other Comprehensive Income (Loss) (AOCI) at March 31, 2021 and 2020, and changes during the three months then ended. TABLE 59: SUMMARY OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED MARCH 31, 2021 (In Millions) NET UNREALIZED GAINS (LOSSES) ON DEBT SECURITIES AVAILABLE FOR SALE (1) NET UNREALIZED (LOSSES) GAINS ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2020 $ 641.8 $ (3.2) $ 144.7 $ (355.3) $ 428.0 Net Change (369.7) (5.2) 5.0 7.8 (362.1) Balance at March 31, 2021 $ 272.1 $ (8.4) $ 149.7 $ (347.5) $ 65.9 (1) Includes net unrealized gains on debt securities transferred from available for sale to held to maturity during the period ended March 31, 2021. THREE MONTHS ENDED MARCH 31, 2020 (In Millions) NET UNREALIZED GAINS (LOSSES) ON DEBT SECURITIES AVAILABLE FOR SALE (1) NET UNREALIZED (LOSSES) GAINS ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2019 $ 114.0 $ (3.7) $ 117.8 $ (422.8) $ (194.7) Net Change 199.7 7.3 25.7 7.0 239.7 Balance at March 31, 2020 $ 313.7 $ 3.6 $ 143.5 $ (415.8) $ 45.0 (1) Includes net unrealized gains on debt securities transferred from available for sale to held to maturity during the period ended March 31, 2020. TABLE 60: DETAILS OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED MARCH 31, 2021 2020 (In Millions) BEFORE TAX TAX EFFECT AFTER TAX BEFORE TAX TAX EFFECT AFTER TAX Unrealized Gains (Losses) on Debt Securities Available for Sale Unrealized Gains (Losses) on Debt Securities Available for Sale $ (496.5) $ 126.8 $ (369.7) $ 266.8 $ (67.1) $ 199.7 Reclassification Adjustment for (Gains) Losses Included in Net Income (1) — — — — — — Net Change $ (496.5) $ 126.8 $ (369.7) $ 266.8 $ (67.1) $ 199.7 Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ (2.5) $ 0.7 $ (1.8) $ 13.3 $ (3.3) $ 10.0 Interest Rate Contracts — — — 0.4 (0.1) 0.3 Reclassification Adjustment for (Gains) Losses Included in Net Income (2) (4.5) 1.1 (3.4) (4.0) 1.0 (3.0) Net Change $ (7.0) $ 1.8 $ (5.2) $ 9.7 $ (2.4) $ 7.3 Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (57.3) $ 0.5 $ (56.8) $ (89.8) $ 9.6 $ (80.2) Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) (0.2) 0.1 (0.1) (0.6) 0.1 (0.5) Net Investment Hedge Gains (Losses) 82.7 (20.8) 61.9 142.7 (36.3) 106.4 Net Change $ 25.2 $ (20.2) $ 5.0 $ 52.3 $ (26.6) $ 25.7 Pension and Other Postretirement Benefit Adjustments Net Actuarial Gains $ (1.3) $ 0.3 $ (1.0) $ (1.3) $ 0.1 $ (1.2) Reclassification Adjustment for (Gains) Losses Included in Net Income (3) Amortization of Net Actuarial Loss 11.9 (2.9) 9.0 10.9 (2.6) 8.3 Amortization of Prior Service Cost (0.3) 0.1 (0.2) (0.1) — (0.1) Net Change $ 10.3 $ (2.5) $ 7.8 $ 9.5 $ (2.5) $ 7.0 Total Net Change $ (468.0) $ 105.9 $ (362.1) $ 338.3 $ (98.6) $ 239.7 (1) The before-tax reclassification adjustment out of AOCI related to the realized gains (losses) on debt securities available for sale is recorded in Investment Security Gains (Losses), net on the consolidated statements of income. (2) See Note 22 — Derivative Financial Instruments for the location of the reclassification adjustment related to cash flow hedges. (3) The before-tax reclassification adjustment out of AOCI related to pension and other postretirement benefit adjustments is recorded in Employee Benefits expense on the consolidated statements of income.

Net Income Per Common Share

Net Income Per Common Share	3 Months Ended
	Mar. 31, 2021
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 61: NET INCOME PER COMMON SHARE THREE MONTHS ENDED MARCH 31, ($ In Millions Except Per Common Share Information) 2021 2020 Basic Net Income Per Common Share Average Number of Common Shares Outstanding 208,112,824 208,881,131 Net Income $ 375.1 $ 360.6 Less: Dividends on Preferred Stock 16.2 30.5 Net Income Applicable to Common Stock 358.9 330.1 Less: Earnings Allocated to Participating Securities 3.7 3.9 Earnings Allocated to Common Shares Outstanding 355.2 326.2 Basic Net Income Per Common Share $ 1.71 $ 1.56 Diluted Net Income Per Common Share Average Number of Common Shares Outstanding 208,112,824 208,881,131 Plus: Dilutive Effect of Share-based Compensation 833,624 935,691 Average Common and Potential Common Shares 208,946,448 209,816,822 Earnings Allocated to Common and Potential Common Shares $ 355.2 $ 326.2 Diluted Net Income Per Common Share 1.70 1.55

Revenue from Contracts with Cli

Revenue from Contracts with Clients	3 Months Ended
	Mar. 31, 2021
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 C&IS clients. Investment Management and Advisory income contains revenue received from providing asset management and related services to Wealth Management and C&IS 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 C&IS clients. Other income largely consists of revenues received from providing employee benefit, investment risk and analytic and other services to C&IS and Wealth Management clients. Other Noninterest Income. Treasury management income represents revenues received from providing cash and liquidity management services to C&IS 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 C&IS 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 C&IS 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 of 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 62: REVENUE DISAGGREGATION THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Noninterest Income Trust, Investment and Other Servicing Fees Custody and Fund Administration $ 469.7 $ 417.6 Investment Management and Advisory 516.4 510.5 Securities Lending 18.3 23.5 Other 59.3 52.0 Total Trust, Investment and Other Servicing Fees $ 1,063.7 $ 1,003.6 Other Noninterest Income Foreign Exchange Trading Income $ 78.7 $ 88.9 Treasury Management Fees 11.2 11.0 Security Commissions and Trading Income 34.8 41.7 Other Operating Income 54.9 34.4 Total Other Noninterest Income $ 179.6 $ 176.0 Total Noninterest Income $ 1,243.3 $ 1,179.6 On the consolidated statements of income, Trust, Investment and Other Servicing Fees and Treasury Management Fees represent revenue from contracts with clients. For the three months ended March 31, 2021, revenue from contracts with clients also includes $28.7 million of the $34.8 million total Security Commissions and Trading Income and $12.8 million of the $54.9 million total Other Operating Income. For the three months ended March 31, 2020, revenue from contracts with clients also includes $29.0 million of the $41.7 million total Security Commissions and Trading Income and $10.8 million of the $34.4 million total Other Operating Income. Receivables Balances. The table below represents receivables balances from contracts with clients, which are included in Other Assets on the consolidated balance sheets, at March 31, 2021 and December 31, 2020. TABLE 63: CLIENT RECEIVABLES (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Trust Fees Receivable, net (1) $ 890.2 $ 819.3 Other 116.2 116.5 Total Client Receivables $ 1,006.4 $ 935.8 (1) Trust Fees Receivable is net of a $6.7 million and $7.2 million fee receivable allowance as of March 31, 2021 and December 31, 2020, respectively.

Net Interest Income

Net Interest Income	3 Months Ended
	Mar. 31, 2021
Banking and Thrift, Interest [Abstract]
Net Interest Income	Net Interest Income The components of Net Interest Income were as follows: TABLE 64: NET INTEREST INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Interest Income Loans and Leases $ 172.0 $ 250.2 Securities — Taxable 173.9 241.1 — Non-Taxable (1) 0.4 0.5 Interest-Bearing Due from and Deposits with Banks (2) 2.4 12.8 Federal Reserve and Other Central Bank Deposits and Other 1.2 24.6 Total Interest Income $ 349.9 $ 529.2 Interest Expense Deposits $ (13.4) $ 60.9 Federal Funds Purchased 0.1 2.0 Securities Sold Under Agreements to Repurchase — 1.0 Other Borrowings 3.5 29.2 Senior Notes 13.7 17.9 Long-Term Debt 5.3 8.4 Floating Rate Capital Debt 0.6 1.7 Total Interest Expense $ 9.8 $ 121.1 Net Interest Income $ 340.1 $ 408.1 (1) Non-Taxable Securities represent securities that are exempt from U.S. federal income taxes. (2) 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.

Other Operating Income

Other Operating Income	3 Months Ended
	Mar. 31, 2021
Other Income and Expenses [Abstract]
Other Operating Income	Other Operating Income The components of Other Operating Income were as follows: TABLE 65: OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Loan Service Fees $ 15.4 $ 11.9 Banking Service Fees 12.7 11.4 Other Income 26.8 11.1 Total Other Operating Income $ 54.9 $ 34.4 Other Operating Income increased compared to the prior-year quarter, primarily due to higher miscellaneous income and a prior-year quarter market value adjustment for a seed capital investment, partially offset by higher expenses for existing swap agreements related to Visa Inc. Class B common shares. The higher miscellaneous income was primarily associated with a market value increase in the supplemental compensation plans, which also resulted in a related increase in supplemental compensation plan expense reported in other operating expense. The components of Other Operating Expense were as follows: TABLE 66: OTHER OPERATING EXPENSE THREE MONTHS ENDED MARCH 31, ($ In Millions) 2021 2020 Business Promotion $ 7.9 $ 18.8 Staff Related 6.8 (3.5) FDIC Insurance Premiums 3.6 2.5 Other Intangibles Amortization 4.3 4.1 Other Expenses 49.1 39.9 Total Other Operating Expense $ 71.7 $ 61.8

Other Operating Expense

Other Operating Expense	3 Months Ended
	Mar. 31, 2021
Other Income and Expenses [Abstract]
Other Operating Expense	Other Operating Income The components of Other Operating Income were as follows: TABLE 65: OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Loan Service Fees $ 15.4 $ 11.9 Banking Service Fees 12.7 11.4 Other Income 26.8 11.1 Total Other Operating Income $ 54.9 $ 34.4 Other Operating Income increased compared to the prior-year quarter, primarily due to higher miscellaneous income and a prior-year quarter market value adjustment for a seed capital investment, partially offset by higher expenses for existing swap agreements related to Visa Inc. Class B common shares. The higher miscellaneous income was primarily associated with a market value increase in the supplemental compensation plans, which also resulted in a related increase in supplemental compensation plan expense reported in other operating expense. The components of Other Operating Expense were as follows: TABLE 66: OTHER OPERATING EXPENSE THREE MONTHS ENDED MARCH 31, ($ In Millions) 2021 2020 Business Promotion $ 7.9 $ 18.8 Staff Related 6.8 (3.5) FDIC Insurance Premiums 3.6 2.5 Other Intangibles Amortization 4.3 4.1 Other Expenses 49.1 39.9 Total Other Operating Expense $ 71.7 $ 61.8

Pension and Postretirement Heal

Pension and Postretirement Health Care	3 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Pension and Postretirement Health Care	Pension and Postretirement Health Care The following table sets forth the net periodic pension and postretirement benefit expense for Northern Trust’s U.S. Qualified Plan, Non-U.S. Pension Plans, U.S. Non-Qualified Plan, and postretirement health care plan for the three months ended March 31, 2021 and 2020. TABLE 67: NET PERIODIC PENSION EXPENSE (BENEFIT) U.S. QUALIFIED PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Service Cost $ 13.2 $ 11.8 Interest Cost 9.8 10.8 Expected Return on Plan Assets (20.1) (19.2) Amortization Net Actuarial Loss 9.4 8.8 Prior Service Cost (0.1) (0.1) Net Periodic Pension Expense $ 12.2 $ 12.1 NON-U.S. PENSION PLANS THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Service Cost $ 0.5 $ 0.5 Interest Cost 0.6 0.7 Expected Return on Plan Assets (0.6) (0.7) Settlement Expense 0.2 0.2 Amortization Net Actuarial Loss 0.3 0.3 Prior Service Cost — — Net Periodic Pension Expense $ 1.0 $ 1.0 U.S. NON-QUALIFIED PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Service Cost $ 1.3 $ 1.1 Interest Cost 0.9 1.2 Amortization Net Actuarial Loss 2.1 1.8 Prior Service Cost — — Net Periodic Pension Expense $ 4.3 $ 4.1 POSTRETIREMENT HEALTH CARE PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Service Cost $ — $ — Interest Cost 0.1 0.2 Amortization Net Actuarial (Gain) (0.1) (0.2) Prior Service Cost (0.2) — Net Periodic Postretirement Expense $ (0.2) $ — Northern Trust changed the plan design of its post-retirement health care plan as of January 1, 2021, which resulted in the recognition of negative prior-service cost at the time these changes were communicated to participants in August 2020. Concurrently, a further shift in population from active to inactive participants required an adjustment to the amortization period from the average remaining service period of active participants to the average life expectancy of the inactive participants. Negative prior service costs are being amortized on a straight-line basis over 13.9 years. 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 three months ended March 31, 2021 and 2020, respectively.

Share-Based Compensation Plans

Share-Based Compensation Plans	3 Months Ended
	Mar. 31, 2021
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. Beginning with the grants made on February 21, 2017 under the Corporation’s prior equity incentive plan, restricted stock unit and performance stock unit grants continue to vest in accordance with the original terms of the award if the applicable employee retires after satisfying applicable age and service requirements. The Corporation granted 729,013 stock unit awards with a total grant-date fair value of $70.4 million during the three months ended March 31, 2021, compared to 763,554 stock unit awards with a total grant-date fair value of $76.2 million during the three months ended March 31, 2020. Compensation expense for the three months ended March 31, 2021 included $21.8 million attributable to restricted stock units granted to retirement-eligible employees that were expensed in their entirety on the date of grant, compared to $23.2 million in the prior-year quarter. There were no non-qualified stock option grants in the three months ended March 31, 2021 and 2020. The Corporation granted 200,066 performance stock units with a total grant-date fair value of $19.5 million during the three months ended March 31, 2021, compared to 205,847 performance stock units with a total grant-date fair value of $20.8 million during the three months ended March 31, 2020. Compensation expense for the three months ended March 31, 2021 included $9.9 million attributable to performance stock units granted to retirement-eligible employees that were expensed in their entirety on the date of grant, compared to $10.8 million in the prior-year quarter. Restricted stock unit award compensation expense for the three months ended March 31, 2021 and 2020 included $4.2 million and $4.3 million, respectively, attributable to restricted stock units vested in full and expensed in their entirety upon date of grant. Total compensation expense for share-based payment arrangements and the associated tax impacts were as follows for the three months ended March 31, 2021 and 2020. TABLE 68: TOTAL COMPENSATION EXPENSE FOR SHARE-BASED PAYMENT ARRANGEMENTS THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Restricted Stock Unit Awards $ 38.4 $ 40.7 Stock Options — 0.2 Performance Stock Units 12.1 12.9 Total Share-Based Compensation Expense 50.5 53.8 Tax Benefits Recognized $ 12.7 $ 13.4

Variable Interest Entities

Variable Interest Entities	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	Variable Interest Entities Variable Interest Entities (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 invests in qualified affordable housing projects and community development entities (collectively, community development projects) that are designed to generate a return primarily through the realization of tax credits. The community development projects are formed as limited partnerships and limited liability companies in which Northern Trust invests as a limited partner/investor member through equity contributions. The economic performance of the community development projects, some of which are VIEs, is subject to the performance of their underlying investment and their ability to operate in compliance with the rules and regulations necessary for the qualification of tax credits generated by equity investments. Northern Trust has determined that it is not the primary beneficiary of any community development project VIEs as it lacks the power to direct the activities that most significantly impact the economic performance of the underlying investments or to affect their ability to operate in compliance with the rules and regulations necessary for the qualification of tax credits generated by equity investments. This power is held by the general partners and managing members who exercise full and exclusive control of the operations of the community development project VIEs. Northern Trust’s maximum exposure to loss as a result of its involvement with community development projects is limited to the carrying amounts of its investments, including any undrawn commitments. As of March 31, 2021 and December 31, 2020, the carrying amounts of these investments in community development projects that generate tax credits, included in Other Assets on the consolidated balance sheets, totaled $908.1 million and $919.6 million, respectively, of which $863.6 million and $874.0 million are VIEs as of March 31, 2021 and December 31, 2020, respectively. As of March 31, 2021 and December 31, 2020, liabilities related to unfunded commitments on investments in tax credit community development projects, included in Other Liabilities on the consolidated balance sheets, totaled $313.7 million and $351.6 million, respectively, of which $298.3 million and $335.9 million related to undrawn commitments on VIEs as of March 31, 2021 and December 31, 2020, respectively. 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 the community development projects. Tax credits and other tax benefits attributable to community development projects totaled $23.0 million and $16.3 million for the three months ended March 31, 2021 and 2020, 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 $50.2 million of money market mutual fund fees for the three months ended March 31, 2021 related to the low-interest-rate environment and certain competitive factors. Northern Trust did not waive any money market mutual fund fees for the three months ended March 31, 2020. 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 March 31, 2021, and December 31, 2020, Northern Trust had no seed capital investments and no unfunded commitments related to seed capital investments.

Commitments and Contingent Liab

Commitments and Contingent Liabilities	3 Months Ended
	Mar. 31, 2021
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 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. The following table provides details of Northern Trust's off-balance sheet financial instruments as of March 31, 2021 and December 31, 2020. TABLE 69: SUMMARY OF OFF-BALANCE SHEET FINANCIAL INSTRUMENTS MARCH 31, 2021 DECEMBER 31, 2020 ($ In Millions) ONE YEAR AND LESS OVER ONE YEAR TOTAL ONE YEAR AND LESS OVER ONE YEAR TOTAL Undrawn Commitments to Extend Credit (1) $ 11,519.7 $ 18,016.0 $ 29,535.7 $ 11,260.5 $ 17,678.0 $ 28,938.5 Standby Letters of Credit and Financial Guarantees (2) 1,474.8 321.0 1,795.8 1,228.1 763.5 1,991.6 Commercial Letters of Credit 66.2 — 66.2 54.6 — 54.6 Custody Securities Lent with Indemnification 176,378.0 — 176,378.0 157,478.0 — 157,478.0 Total Off-Balance Sheet Financial Instruments $ 189,438.7 $ 18,337.0 $ 207,775.7 $ 170,021.2 $ 18,441.5 $ 188,462.7 (1) These amounts exclude $404.2 million and $384.7 million of commitments participated to others at March 31, 2021 and December 31, 2020, respectively. (2) These amounts include $23.8 million and $24.2 million of standby letters of credit secured by cash deposits or participated to others as of March 31, 2021 and December 31, 2020, respectively. Undrawn Commitments to Extend Credit 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. Custody Securities Lent with Indemnification involves Northern Trust lending securities owned by clients to borrowers who are reviewed and approved by the Northern Trust Capital Markets Credit Committee, as part of its securities custody activities and at the direction of its clients. In connection with these activities, Northern Trust has issued indemnifications to certain clients against certain losses that are a direct result of a borrower’s failure to return securities when due, should the value of such securities exceed the value of the collateral required to be posted. Borrowers are required to collateralize fully securities received with cash or marketable securities. As securities are loaned, collateral is maintained at a minimum of 100% of the fair value of the securities plus accrued interest. The collateral is revalued on a daily basis. The amount of securities loaned as of March 31, 2021 and December 31, 2020 subject to indemnification was $176.4 billion and $157.5 billion, respectively. Because of the credit quality of the borrowers and the requirement to fully collateralize securities borrowed, management believes that the exposure to credit loss from this activity is not significant and no liability was recorded as of March 31, 2021 or December 31, 2020, related to these indemnifications. Legal Proceedings. In the normal course of business, the Corporation and its subsidiaries are routinely defendants in or parties to pending and threatened legal actions, and are subject to regulatory examinations, information-gathering requests, investigations, and proceedings, both formal and informal. In certain legal actions, claims for substantial monetary damages are asserted. In regulatory matters, claims for disgorgement, restitution, penalties and/or other remedial actions or sanctions may be sought. Based on current knowledge, after consultation with legal counsel and after taking into account current accruals, management does not believe that losses, fines or penalties, if any, arising from pending litigation or threatened legal actions or regulatory matters either individually or in the aggregate, after giving effect to applicable reserves and insurance coverage will have a material adverse effect on the consolidated financial position or liquidity of the Corporation, although such matters could have a material adverse effect on the Corporation’s operating results for a particular period. Under GAAP, (i) an event is “probable” if the “future event or events are likely to occur”; (ii) an event is “reasonably possible” if “the chance of the future event or events occurring is more than remote but less than likely”; and (iii) an event is “remote” if “the chance of the future event or events occurring is slight.” The outcome of litigation and regulatory matters is inherently difficult to predict and/or the range of loss often cannot be reasonably estimated, particularly for matters that (i) will be decided by a jury, (ii) are in early stages, (iii) involve uncertainty as to the likelihood of a class being certified or the ultimate size of the class, (iv) are subject to appeals or motions, (v) involve significant factual issues to be resolved, including with respect to the amount of damages, (vi) do not specify the amount of damages sought or (vii) seek very large damages based on novel and complex damage and liability legal theories. Accordingly, the Corporation cannot reasonably estimate the eventual outcome of these pending matters, the timing of their ultimate resolution or what the eventual loss, fines or penalties, if any, related to each pending matter will be. In accordance with applicable accounting guidance, the Corporation records accruals for litigation and regulatory matters when those matters present loss contingencies that are both probable and reasonably estimable. When loss contingencies are not both probable and reasonably estimable, the Corporation does not record accruals. No material accruals have been recorded for pending litigation or threatened legal actions or regulatory matters. For a limited number of matters for which a loss is reasonably possible in future periods, whether in excess of an accrued liability or where there is no accrued liability, the Corporation is able to estimate a range of possible loss. As of March 31, 2021, 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. The re-trial proceedings in the appellate court have not yet been scheduled. 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 selling 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. On June 28, 2018, and September 27, 2019, Visa deposited an additional $600 million and $300 million, respectively, 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. 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. In June 2016 and 2015, Northern Trust recorded a $123.1 million and $99.9 million net gain on the sale of 1.1 million and 1.0 million of its Visa Class B common shares, respectively. These sales do not affect Northern Trust’s risk related to the impact of the covered litigation on the rate at which such shares will ultimately convert into Visa Class A common shares. Northern Trust continued to hold approximately 4.1 million Visa Class B common shares, which are recorded at their original cost basis of zero, as of March 31, 2021 and December 31, 2020.

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments Northern Trust is a party to various derivative financial instruments that are used in the normal course of business to meet the needs of its clients, as part of its trading activity for its own account and as part of its risk management activities. These instruments may include foreign exchange contracts, interest rate contracts, total return swap contracts, and swaps related to the sale of certain Visa Class B common shares. Foreign exchange contracts are agreements to exchange specific amounts of currencies at a future date, at a specified rate of exchange. Foreign exchange contracts are entered into primarily to meet the foreign exchange needs of clients. Foreign exchange contracts are also used for trading and risk management purposes. For risk management purposes, Northern Trust uses foreign exchange contracts to reduce its exposure to changes in foreign exchange rates relating to certain forecasted non-functional-currency-denominated revenue and expenditure transactions, foreign-currency-denominated assets and liabilities, including debt securities, and net investments in non-U.S. affiliates. Interest rate contracts include swap and option contracts. Interest rate swap contracts involve the exchange of fixed and floating rate interest payment obligations without the exchange of the underlying principal amounts. Northern Trust enters into interest rate swap contracts with its clients and also may utilize such contracts to reduce or eliminate the exposure to changes in the cash flows or fair value of hedged assets or liabilities due to changes in interest rates. Interest rate option contracts may include caps, floors, collars and swaptions, and provide for the transfer or reduction of interest rate risk, typically in exchange for a fee. Northern Trust enters into option contracts primarily as a seller of interest rate protection to clients. Northern Trust receives a fee at the outset of the agreement for the assumption of the risk of an unfavorable change in interest rates. This assumed interest rate risk is then mitigated by entering into an offsetting position with an outside counterparty. Northern Trust may also purchase or enter into option contracts for risk management purposes including to reduce the exposure to changes in the cash flows of hedged assets due to changes in interest rates. The following table shows the notional and fair values of all derivative financial instruments as of March 31, 2021 and December 31, 2020. TABLE 70: NOTIONAL AND FAIR VALUES OF DERIVATIVE FINANCIAL INSTRUMENTS MARCH 31, 2021 DECEMBER 31, 2020 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 $ 4,513.7 $ 10.0 $ 13.7 $ 4,717.6 $ 8.2 $ 10.2 Cash Flow Hedges — — — 50.0 0.1 — Foreign Exchange Contracts Cash Flow Hedges 6,464.9 296.7 20.4 6,554.4 15.4 104.0 Net Investment Hedges 3,482.1 73.5 8.8 3,480.3 0.1 207.7 Total Derivatives Designated as Hedging under GAAP $ 14,460.7 $ 380.2 $ 42.9 $ 14,802.3 $ 23.8 $ 321.9 Derivatives Not Designated as Hedging under GAAP Non-Designated Risk Management Derivatives Foreign Exchange Contracts $ 131.0 $ 0.7 $ 0.1 $ 67.7 $ 0.1 $ 0.1 Other Financial Derivatives (3) 721.5 — 34.6 745.4 — 35.3 Total Non-Designated Risk Management Derivatives $ 852.5 $ 0.7 $ 34.7 $ 813.1 $ 0.1 $ 35.4 Client-Related and Trading Derivatives Foreign Exchange Contracts $ 309,731.3 $ 2,630.1 $ 2,513.7 $ 320,563.4 $ 4,245.1 $ 4,410.7 Interest Rate Contracts 10,702.2 195.6 110.0 10,573.3 289.2 114.8 Total Client-Related and Trading Derivatives $ 320,433.5 $ 2,825.7 $ 2,623.7 $ 331,136.7 $ 4,534.3 $ 4,525.5 Total Derivatives Not Designated as Hedging under GAAP $ 321,286.0 $ 2,826.4 $ 2,658.4 $ 331,949.8 $ 4,534.4 $ 4,560.9 Total Gross Derivatives $ 335,746.7 $ 3,206.6 $ 2,701.3 $ 346,752.1 $ 4,558.2 $ 4,882.8 Less: Netting (4) 1,977.1 2,090.3 3,507.8 2,817.1 Total Derivative Financial Instruments $ 1,229.5 $ 611.0 $ 1,050.4 $ 2,065.7 (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. (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 available for sale debt securities and long-term subordinated debt and senior notes. Northern Trust applied the “shortcut” method of accounting, available under GAAP, which assumes there is perfect effectiveness in a hedge, for all of its fair value hedges during the three-month periods ended March 31, 2021 and 2020. 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. Northern Trust also enters into interest rate contracts to hedge changes in cash flows due to movements in interest rates of available for sale debt securities. The change in fair value of cash flow hedging derivative instruments are recorded in AOCI and reclassified to earnings when the hedged forecasted transaction impacts earnings within the same income statement line item. There were no material gains or losses reclassified into earnings during the three-month periods ended March 31, 2021 and 2020, as a result of the discontinuance of forecasted transactions that were no longer probable of occurring. It is estimated that net losses of $8.0 million and gains of $287.9 million will be reclassified into net income within the next twelve months relating to cash flow hedges of foreign-currency-denominated transactions and cash flow hedges of foreign-currency-denominated debt securities, respectively. As of March 31, 2021, 23 months was the maximum length of time over which the exposure to variability in future cash flows of forecasted foreign-currency-denominated transactions was being hedged. The following tables provide fair value and cash flow hedge derivative gains and losses recognized in income during the three-month periods ended March 31, 2021 and 2020. TABLE 71: LOCATION AND AMOUNT OF FAIR VALUE AND CASH FLOW HEDGE DERIVATIVE GAINS AND LOSSES RECORDED IN INCOME (In Millions) INTEREST INCOME INTEREST EXPENSE OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, 2021 2020 2021 2020 2021 2020 Total amounts on the consolidated statements of income $ 349.9 $ 529.2 $ 9.8 $ 121.1 $ 54.9 $ 34.4 Gains (Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives 18.4 (76.0) (142.9) 150.4 — — Recognized on hedged items (18.4) 76.0 142.9 (150.4) — — Amounts related to interest settlements on derivatives (1.6) (0.5) 7.0 (2.9) — — Total gains (losses) recognized on fair value hedges $ (1.6) $ (0.5) $ 7.0 $ (2.9) $ — $ — Gains (Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gains (losses) reclassified from AOCI to net income $ 5.5 $ 4.1 $ — $ — $ (1.0) $ (0.1) Total gains (losses) reclassified from AOCI to net income on cash flow hedges $ 5.5 $ 4.1 $ — $ — $ (1.0) $ (0.1) The following table provides the impact of fair value hedge accounting on the carrying value of the designated hedged items as of March 31, 2021 and December 31, 2020. TABLE 72: HEDGED ITEMS IN FAIR VALUE HEDGES MARCH 31, 2021 DECEMBER 31, 2020 (In Millions) CARRYING VALUE OF THE HEDGED ITEMS CUMULATIVE HEDGE ACCOUNTING BASIS ADJUSTMENT (1) CARRYING VALUE OF THE HEDGED ITEMS CUMULATIVE HEDGE ACCOUNTING BASIS ADJUSTMENT (2) Available for Sale Debt Securities (3) $ 1,807.4 $ 35.3 $ 2,075.1 $ 48.8 Senior Notes and Long-Term Subordinated Debt 2,745.2 66.5 2,745.1 221.5 Total $ 4,552.6 $ 101.8 $ 4,820.2 $ 270.3 (1) The cumulative hedge accounting basis adjustment includes $10.2 million related to discontinued hedging relationships of available for sale debt securities as of March 31, 2021. 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 March 31, 2021. (2) The cumulative hedge accounting basis adjustment includes $10.4 million related to discontinued hedging relationships of available for sale debt securities as of December 31, 2020. 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, 2020. (3) 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 $82.7 million and $142.7 million were recognized in AOCI related to foreign exchange contracts for the three months ended March 31, 2021 and 2020, 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 months ended March 31, 2021 and 2020 for derivative instruments not designated as hedges under GAAP. TABLE 73: LOCATION AND AMOUNT OF GAINS AND LOSSES RECORDED IN INCOME FOR DERIVATIVES NOT DESIGNATED AS HEDGING UNDER GAAP (In Millions) DERIVATIVE GAINS (LOSSES) LOCATION RECOGNIZED IN INCOME AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME THREE MONTHS ENDED MARCH 31, 2021 2020 Non-designated risk management derivatives Foreign Exchange Contracts Other Operating Income $ 0.1 $ 0.1 Other Financial Derivatives (1) Other Operating Income (3.6) 2.9 Gains (Losses) from non-designated risk management derivatives $ (3.5) $ 3.0 Client-related and trading derivatives Foreign Exchange Contracts Foreign Exchange Trading Income $ 78.7 $ 88.9 Interest Rate Contracts Security Commissions and Trading Income 3.0 11.0 Gains (Losses) from client-related and trading derivatives $ 81.7 $ 99.9 Total gains (losses) from derivatives not designated as hedging under GAAP $ 78.2 $ 102.9 (1) This line includes swaps related to the sale of certain Visa Class B common shares.

Offsetting of Assets and Liabil

Offsetting of Assets and Liabilities	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Offsetting of Assets and Liabilities	Offsetting of Assets and 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. The following table provides information regarding the offsetting of derivative assets and securities purchased under agreements to resell within the consolidated balance sheets as of March 31, 2021 and December 31, 2020. TABLE 74: OFFSETTING OF DERIVATIVE ASSETS AND SECURITIES PURCHASED UNDER AGREEMENTS TO RESELL MARCH 31, 2021 (In Millions) GROSS RECOGNIZED ASSETS GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (2) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET NET AMOUNT (3) Derivative Assets (1) Foreign Exchange Contracts Over the Counter (OTC) $ 2,303.8 $ 1,973.5 $ 330.3 $ 8.4 $ 321.9 Interest Rate Swaps OTC 204.0 3.6 200.4 — 200.4 Interest Rate Swaps Exchange Cleared 1.6 — 1.6 — 1.6 Total Derivatives Subject to a Master Netting Arrangement 2,509.4 1,977.1 532.3 8.4 523.9 Total Derivatives Not Subject to a Master Netting Arrangement 697.2 — 697.2 — 697.2 Total Derivatives 3,206.6 1,977.1 1,229.5 8.4 1,221.1 Securities Purchased under Agreements to Resell $ 1,109.3 $ — $ 1,109.3 $ 1,109.3 $ — DECEMBER 31, 2020 (In Millions) GROSS RECOGNIZED ASSETS GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (2) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET NET AMOUNT (3) Derivative Assets (1) Foreign Exchange Contracts OTC $ 3,799.7 $ 3,505.3 $ 294.4 $ 0.9 $ 293.5 Interest Rate Swaps OTC 295.9 2.5 293.4 — 293.4 Interest Rate Swaps Exchange Cleared 1.6 — 1.6 — 1.6 Total Derivatives Subject to a Master Netting Arrangement 4,097.2 3,507.8 589.4 0.9 588.5 Total Derivatives Not Subject to a Master Netting Arrangement 461.0 — 461.0 — 461.0 Total Derivatives 4,558.2 3,507.8 1,050.4 0.9 1,049.5 Securities Purchased under Agreements to Resell $ 1,596.5 $ — $ 1,596.5 $ 1,596.5 $ — (1) Derivative assets are reported in Other Assets on the consolidated balance sheets. Other Assets (excluding derivative assets) totaled $7.6 billion and $7.3 billion as of March 31, 2021 and December 31, 2020, respectively. (2) Including cash collateral received from counterparties. (3) Northern Trust did not possess any cash collateral that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2021 and December 31, 2020. The following table provides information regarding the offsetting of derivative liabilities and securities sold under agreements to repurchase within the consolidated balance sheets as of March 31, 2021 and December 31, 2020. TABLE 75: OFFSETTING OF DERIVATIVE LIABILITIES AND SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE MARCH 31, 2021 (In Millions) GROSS RECOGNIZED LIABILITIES GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (2) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET NET AMOUNT (3) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 2,093.4 $ 2,023.7 $ 69.7 $ 0.9 $ 68.8 Interest Rate Swaps OTC 123.7 66.6 57.1 — 57.1 Other Financial Derivatives 34.6 — 34.6 — 34.6 Total Derivatives Subject to a Master Netting Arrangement 2,251.7 2,090.3 161.4 0.9 160.5 Total Derivatives Not Subject to a Master Netting Arrangement 449.6 — 449.6 — 449.6 Total Derivatives 2,701.3 2,090.3 611.0 0.9 610.1 Securities Sold under Agreements to Repurchase $ 95.6 $ — $ 95.6 $ 95.6 $ — DECEMBER 31, 2020 (In Millions) GROSS RECOGNIZED LIABILITIES GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (2) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET NET AMOUNT (3) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 3,577.7 $ 2,718.6 $ 859.1 $ 0.5 $ 858.6 Interest Rate Swaps OTC 125.0 98.5 26.5 — 26.5 Interest Rate Swaps Exchange Cleared — — — — — Other Financial Derivatives 35.3 — 35.3 — 35.3 Total Derivatives Subject to a Master Netting Arrangement 3,738.0 2,817.1 920.9 0.5 920.4 Total Derivatives Not Subject to a Master Netting Arrangement 1,144.8 — 1,144.8 — 1,144.8 Total Derivatives 4,882.8 2,817.1 2,065.7 0.5 2,065.2 Securities Sold under Agreements to Repurchase $ 39.8 $ — $ 39.8 $ 39.8 $ — (1) Derivative liabilities are reported in Other Liabilities on the consolidated balance sheets. Other Liabilities (excluding derivative liabilities) totaled $4.4 billion and $3.5 billion as of March 31, 2021 and December 31, 2020, respectively. (2) Including cash collateral deposited with counterparties. (3) Northern Trust did not place any cash collateral with counterparties that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2021 and December 31, 2020. 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. However, Northern Trust’s repurchase agreements and reverse repurchase agreements do not meet the requirements to net under GAAP. 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 $189.0 million and $206.1 million, respectively, as of March 31, 2021, and $111.0 million and $49.0 million, respectively, as of December 31, 2020, 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 $401.6 million and $1,648.2 million at March 31, 2021 and December 31, 2020, respectively. Cash collateral amounts deposited with derivative counterparties on those dates included $391.1 million and $1,044.0 million, respectively, posted against these liabilities, resulting in a net maximum amount of termination payments that could have been required at March 31, 2021 and December 31, 2020, of $10.5 million and $604.2 million, respectively. Accelerated settlement of these liabilities would not have a material effect on the consolidated financial position or liquidity of Northern Trust.

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2021
Accounting Changes and Error Corrections [Abstract]
Basis of Presentation	The consolidated financial statements include the accounts of Northern Trust Corporation (Corporation) and its wholly-owned subsidiary, The Northern Trust Company (Bank), and various other wholly-owned subsidiaries of the Corporation and Bank. Throughout the notes to the consolidated financial statements, the term “Northern Trust” refers to the Corporation and its subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements, as of and for the periods ended March 31, 2021 and 2020, 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. The consolidated statements of income include results of acquired subsidiaries from the dates of acquisition. Certain prior-period balances have been reclassified to conform with the current year’s presentation.
Recent Accounting Pronouncements	On January 1, 2021, Northern Trust adopted Accounting Standards Update (ASU) No. 2020-01, “Investments—Equity Securities (Topic 321), Investments—Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815): Clarifying the Interactions between Topic 321, Topic 323, and Topic 815” (ASU 2020-01). ASU 2020-01 addresses two accounting issues: (1) application of the measurement alternative under Topic 321 in correlation with the transition into and out of the equity method under Topic 323 and (2) the measurement of certain forward contracts and purchased options to acquire equity securities. ASU 2020-01 clarifies that an entity applying the measurement alternative under Topic 321 that must transition to the equity method under Topic 323 because of an observable transaction will remeasure its investment immediately before transition, whereas an entity applying the equity method under Topic 323 that must transition to Topic 321 because of an observable transaction will remeasure its investment immediately after transition. ASU 2020-01 also clarifies that certain forward contracts or purchased call options to acquire equity securities generally will be measured using the fair value principles of Topic 321 before settlement or exercise. Upon adoption of ASU 2020-01, there was no significant impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. On January 1, 2021, Northern Trust adopted ASU No. 2020-08, “Codification Improvements to Subtopic 310-20, Receivables—Nonrefundable Fees and Other Costs” (ASU 2020-08). ASU 2020-08 clarifies the Codification related to the standard issued in ASU No. 2017-08, “Receivables—Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Debt Securities”. ASU 2020-08 clarifies that an entity should amortize premiums on purchased callable debt securities to the first call date and related call amount and at that point reassess if there is a remaining premium to amortize to a subsequent call date. Upon adoption of ASU 2020-08, there was no significant impact to Northern Trust’s consolidated balance sheets or consolidated statements of income. On January 7, 2021, Northern Trust retrospectively adopted ASU No. 2021-01, “Reference Rate Reform (Topic 848): Scope” (ASU 2021-01). ASU 2021-01 clarifies the scope of Topic 848 to explicitly include those derivative instruments affected by changes in interest rates used for margining, discounting, or contract price alignment as eligible for certain optional expedients and exceptions in Topic 848. Upon adoption of ASU 2021-01, Northern Trust elected the expedients provided in Topic 848 with no significant impact on Northern Trust’s consolidated balance sheets or consolidated statements of income.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurement Inputs and Valuation Techniques	The following table presents the fair values of Northern Trust’s Level 3 liabilities as of March 31, 2021 and December 31, 2020, 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 29: LEVEL 3 SIGNIFICANT UNOBSERVABLE INPUTS MARCH 31, 2021 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 $34.6 million Discounted Cash Flow Conversion Rate 1.62x 1.62x Visa Class A Appreciation 9.63% 9.63% Expected Duration 12 - 33 months 20 months (1) Weighted average of expected duration based on scenario probability. DECEMBER 31, 2020 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 $35.3 million Discounted Cash Flow Conversion Rate 1.62x 1.62x Visa Class A Appreciation 8.73% 8.73% 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 March 31, 2021 and December 31, 2020, 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 32: LEVEL 3 NONRECURRING BASIS SIGNIFICANT UNOBSERVABLE INPUTS MARCH 31, 2021 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $16.7 million Market Approach Discount factor applied to real estate collateral-based loans to reflect realizable value 15.0% - 20.0% 15.8% (1) Includes real estate collateral-based loans and other collateral-based loans. DECEMBER 31, 2020 FINANCIAL INSTRUMENT FAIR VALUE (1) VALUATION TECHNIQUE UNOBSERVABLE INPUTS INPUT VALUES WEIGHTED-AVERAGE INPUT VALUES Loans $24.6 million Market Approach Discount factor applied to real estate collateral-based loans to reflect realizable value 15.0 % - 20.0% 16.8% (1) Includes real estate collateral-based loans and other collateral-based loans.
Recurring Basis Hierarchy Leveling	The following table presents assets and liabilities measured at fair value on a recurring basis as of March 31, 2021 and December 31, 2020, segregated by fair value hierarchy level. TABLE 30: RECURRING BASIS HIERARCHY LEVELING MARCH 31, 2021 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 2,561.0 $ — $ — $ — $ 2,561.0 Obligations of States and Political Subdivisions — 3,279.8 — — 3,279.8 Government Sponsored Agency — 24,650.7 — — 24,650.7 Non-U.S. Government — 558.1 — — 558.1 Corporate Debt — 2,398.7 — — 2,398.7 Covered Bonds — 544.1 — — 544.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 3,003.4 — — 3,003.4 Other Asset-Backed — 4,783.0 — — 4,783.0 Commercial Mortgage-Backed — 1,099.8 — — 1,099.8 Total Available for Sale 2,561.0 40,317.6 — — 42,878.6 Trading Account — 0.4 — — 0.4 Total Available for Sale and Trading Debt Securities 2,561.0 40,318.0 — — 42,879.0 Other Assets Derivative Assets Foreign Exchange Contracts — 3,001.0 — (1,973.5) 1,027.5 Interest Rate Contracts — 205.6 — (3.6) 202.0 Total Derivative Assets — 3,206.6 — (1,977.1) 1,229.5 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 2,543.0 — (2,023.7) 519.3 Interest Rate Contracts — 123.7 — (66.6) 57.1 Other Financial Derivatives (1) — — 34.6 — 34.6 Total Derivative Liabilities $ — $ 2,666.7 $ 34.6 $ (2,090.3) $ 611.0 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of March 31, 2021, derivative assets and liabilities shown above also include reductions of $449.1 million and $562.3 million, 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, 2020 (In Millions) LEVEL 1 LEVEL 2 LEVEL 3 NETTING ASSETS/LIABILITIES AT FAIR VALUE Debt Securities Available for Sale U.S. Government $ 2,799.9 $ — $ — $ — $ 2,799.9 Obligations of States and Political Subdivisions — 3,083.6 — — 3,083.6 Government Sponsored Agency — 24,956.7 — — 24,956.7 Non-U.S. Government — 714.0 — — 714.0 Corporate Debt — 2,539.6 — — 2,539.6 Covered Bonds — 553.1 — — 553.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,345.8 — — 2,345.8 Other Asset-Backed — 3,997.5 — — 3,997.5 Commercial Mortgage-Backed — 1,031.8 — — 1,031.8 Total Available for Sale 2,799.9 39,222.1 — — 42,022.0 Trading Account — 0.5 — — 0.5 Total Available for Sale and Trading Debt Securities 2,799.9 39,222.6 — — 42,022.5 Other Assets Derivative Assets Foreign Exchange Contracts — 4,260.7 — (3,505.3) 755.4 Interest Rate Contracts — 297.5 — (2.5) 295.0 Total Derivative Assets — 4,558.2 — (3,507.8) 1,050.4 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 4,722.5 — (2,718.6) 2,003.9 Interest Rate Contracts — 125.0 — (98.5) 26.5 Other Financial Derivatives (1) — — 35.3 — 35.3 Total Derivative Liabilities $ — $ 4,847.5 $ 35.3 $ (2,817.1) $ 2,065.7 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, 2020, derivative assets and liabilities shown above also include reductions of $1,867.8 million and $1,177.2 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties.
Changes in Level 3 Liabilities	The following table presents the changes in Level 3 liabilities for the three months ended March 31, 2021 and 2020. TABLE 31: CHANGES IN LEVEL 3 LIABILITIES (In Millions) SWAPS RELATED TO SALE OF CERTAIN VISA CLASS B COMMON SHARES THREE MONTHS ENDED MARCH 31, 2021 2020 Fair Value at January 1 $ 35.3 $ 33.4 Total (Gains) Losses: Included in Earnings (1) 3.6 (2.9) Purchases, Issues, Sales, and Settlements Settlements (4.3) (4.0) Fair Value at March 31 $ 34.6 $ 26.5 (1) (Gains) losses are recorded in Other Operating Income on the consolidated statements of income.
Fair Value of Financial Instruments	The following table summarizes the fair values of all financial instruments. TABLE 33: FAIR VALUE OF FINANCIAL INSTRUMENTS MARCH 31, 2021 FAIR VALUE (In Millions) BOOK VALUE TOTAL FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 ASSETS Cash and Due from Banks $ 4,584.4 $ 4,584.4 $ 4,584.4 $ — $ — Federal Reserve and Other Central Bank Deposits 46,911.4 46,911.4 — 46,911.4 — Interest-Bearing Deposits with Banks 5,142.8 5,142.8 — 5,142.8 — Federal Funds Sold 0.1 0.1 — 0.1 — Securities Purchased under Agreements to Resell 1,109.3 1,109.3 — 1,109.3 — Debt Securities Available for Sale (1) 42,878.6 42,878.6 2,561.0 40,317.6 — Held to Maturity 17,136.4 17,100.0 100.0 17,000.0 — Trading Account 0.4 0.4 — 0.4 — Loans (excluding Leases) Held for Investment 34,168.1 34,181.7 — — 34,181.7 Client Security Settlement Receivables 1,970.2 1,970.2 — 1,970.2 — Other Assets Federal Reserve and Federal Home Loan Bank Stock 230.0 230.0 — 230.0 — Community Development Investments 908.1 908.1 — 908.1 — Employee Benefit and Deferred Compensation 230.3 234.5 133.9 100.6 — LIABILITIES Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 72,801.2 $ 72,801.2 $ 72,801.2 $ — $ — Savings Certificates and Other Time 909.7 911.0 — 911.0 — Non U.S. Offices Interest-Bearing 63,746.5 63,746.5 — 63,746.5 — Federal Funds Purchased 0.2 0.2 — 0.2 — Securities Sold Under Agreements to Repurchase 95.6 95.6 — 95.6 — Other Borrowings 5,428.4 5,428.6 — 5,428.6 — Senior Notes 2,991.2 3,083.9 — 3,083.9 — Long-Term Debt Subordinated Debt 1,165.9 1,211.5 — 1,211.5 — Floating Rate Capital Debt 277.8 268.7 — 268.7 — Other Liabilities Standby Letters of Credit 18.7 18.7 — — 18.7 Loan Commitments 76.9 76.9 — — 76.9 Derivative Instruments Asset/Liability Management Foreign Exchange Contracts Assets $ 370.9 $ 370.9 $ — $ 370.9 $ — Liabilities 29.3 29.3 — 29.3 — Interest Rate Contracts Assets 10.0 10.0 — 10.0 — Liabilities 13.7 13.7 — 13.7 — Other Financial Derivatives Liabilities (2) 34.6 34.6 — — 34.6 Client-Related and Trading Foreign Exchange Contracts Assets 2,630.1 2,630.1 — 2,630.1 — Liabilities 2,513.7 2,513.7 — 2,513.7 — Interest Rate Contracts Assets 195.6 195.6 — 195.6 — Liabilities 110.0 110.0 — 110.0 — (1) Refer to the table located on page 34 for the disaggregation of available for sale debt securities. (2) This line consists of swaps related to the sale of certain Visa Class B common shares. DECEMBER 31, 2020 FAIR VALUE (In Millions) BOOK VALUE TOTAL FAIR VALUE LEVEL 1 LEVEL 2 LEVEL 3 ASSETS Cash and Due from Banks $ 4,389.5 $ 4,389.5 $ 4,389.5 $ — $ — Federal Reserve and Other Central Bank Deposits 55,503.6 55,503.6 — 55,503.6 — Interest-Bearing Deposits with Banks 4,372.6 4,372.6 — 4,372.6 — Securities Purchased under Agreements to Resell 1,596.5 1,596.5 — 1,596.5 — Debt Securities Available for Sale (1) 42,022.0 42,022.0 2,799.9 39,222.1 — Held to Maturity 17,791.1 17,797.4 90.0 17,707.4 — Trading Account 0.5 0.5 — 0.5 — Loans (excluding Leases) Held for Investment 33,558.0 34,017.5 — — 34,017.5 Client Security Settlement Receivables 1,160.2 1,160.2 — 1,160.2 — Other Assets Federal Reserve and Federal Home Loan Bank Stock 275.0 275.0 — 275.0 — Community Development Investments 919.6 919.6 — 919.6 — Employee Benefit and Deferred Compensation 215.8 228.9 138.6 90.3 — LIABILITIES Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 71,742.5 $ 71,742.5 $ 71,742.5 $ — $ — Savings Certificates and Other Time 937.1 943.0 — 943.0 — Non U.S. Offices Interest-Bearing 71,198.4 71,198.4 — 71,198.4 — Federal Funds Purchased 260.2 260.2 — 260.2 — Securities Sold Under Agreements to Repurchase 39.8 39.8 — 39.8 — Other Borrowings 4,011.5 4,012.7 — 4,012.7 — Senior Notes 3,122.4 3,222.6 — 3,222.6 — Long-Term Debt Subordinated Debt 1,189.3 1,250.1 — 1,250.1 — Floating Rate Capital Debt 277.8 264.6 — 264.6 — Other Liabilities Standby Letters of Credit 22.4 22.4 — — 22.4 Loan Commitments 77.0 77.0 — — 77.0 Derivative Instruments Asset/Liability Management Foreign Exchange Contracts Assets $ 15.6 $ 15.6 $ — $ 15.6 $ — Liabilities 311.8 311.8 — 311.8 — Interest Rate Contracts Assets 8.3 8.3 — 8.3 — Liabilities 10.2 10.2 — 10.2 — Other Financial Derivatives Liabilities (2) 35.3 35.3 — — 35.3 Client-Related and Trading Foreign Exchange Contracts Assets 4,245.1 4,245.1 — 4,245.1 — Liabilities 4,410.7 4,410.7 — 4,410.7 — Interest Rate Contracts Assets 289.2 289.2 — 289.2 — Liabilities 114.8 114.8 — 114.8 — (1) Refer to the table located on page 35 for the disaggregation of available for sale debt securities. (2) This line consists of swaps related to the sale of certain Visa Class B common shares.

Securities (Tables)

Securities (Tables)	3 Months Ended
	Mar. 31, 2021
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 at March 31, 2021 and December 31, 2020, and remaining maturities of debt securities available for sale at March 31, 2021. TABLE 34: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF DEBT SECURITIES AVAILABLE FOR SALE MARCH 31, 2021 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 2,521.1 $ 50.6 $ 10.7 $ 2,561.0 Obligations of States and Political Subdivisions 3,249.8 82.5 52.5 3,279.8 Government Sponsored Agency 24,535.5 275.4 160.2 24,650.7 Non-U.S. Government 564.3 0.1 6.3 558.1 Corporate Debt 2,336.3 65.2 2.8 2,398.7 Covered Bonds 535.8 8.3 — 544.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,968.8 54.0 19.4 3,003.4 Other Asset-Backed 4,749.5 38.0 4.5 4,783.0 Commercial Mortgage-Backed 1,047.5 53.6 1.3 1,099.8 Total $ 42,508.6 $ 627.7 $ 257.7 $ 42,878.6 DECEMBER 31, 2020 (In Millions) AMORTIZED COST GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR VALUE U.S. Government $ 2,728.8 $ 71.1 $ — $ 2,799.9 Obligations of States and Political Subdivisions 2,927.8 155.9 0.1 3,083.6 Government Sponsored Agency 24,595.1 388.5 26.9 24,956.7 Non-U.S. Government 713.6 1.1 0.7 714.0 Corporate Debt 2,459.9 79.8 0.1 2,539.6 Covered Bonds 543.1 10.0 — 553.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,281.7 64.7 0.6 2,345.8 Other Asset-Backed 3,953.5 46.8 2.8 3,997.5 Commercial Mortgage-Backed 952.2 79.7 0.1 1,031.8 Total $ 41,155.7 $ 897.6 $ 31.3 $ 42,022.0
Remaining Maturity of Securities Available for Sale and Held to Maturity	TABLE 35: REMAINING MATURITY OF DEBT SECURITIES AVAILABLE FOR SALE MARCH 31, 2021 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 $ 99.9 $ 101.5 $ 1,874.1 $ 1,911.3 $ 547.1 $ 548.2 $ — $ — $ 2,521.1 $ 2,561.0 Obligations of States and Political Subdivisions 7.2 7.3 294.8 308.4 2,764.2 2,787.5 183.6 176.6 3,249.8 3,279.8 Government Sponsored Agency 4,859.6 4,913.7 8,260.4 8,330.3 8,833.7 8,816.8 2,581.8 2,589.9 24,535.5 24,650.7 Non-U.S. Government 269.6 269.6 40.5 40.5 254.2 248.0 — — 564.3 558.1 Corporate Debt 372.6 376.5 1,950.5 2,009.1 9.3 9.2 3.9 3.9 2,336.3 2,398.7 Covered Bonds 106.8 107.1 429.0 437.0 — — — — 535.8 544.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 534.4 537.5 2,001.7 2,043.0 432.7 422.9 — — 2,968.8 3,003.4 Other Asset-Backed 733.9 742.4 3,201.6 3,228.2 739.2 737.8 74.8 74.6 4,749.5 4,783.0 Commercial Mortgage-Backed 17.8 17.8 510.0 532.5 511.6 541.4 8.1 8.1 1,047.5 1,099.8 Total $ 7,001.8 $ 7,073.4 $ 18,562.6 $ 18,840.3 $ 14,092.0 $ 14,111.8 $ 2,852.2 $ 2,853.1 $ 42,508.6 $ 42,878.6 Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments. TABLE 38: REMAINING MATURITY OF DEBT SECURITIES HELD TO MATURITY MARCH 31, 2021 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 $ 100.0 $ 100.0 $ — $ — $ — $ — $ — $ — $ 100.0 $ 100.0 Obligations of States and Political Subdivisions 1.0 1.0 — — — — — — 1.0 1.0 Government Sponsored Agency 2.0 2.0 8.0 8.0 9.2 9.2 34.4 33.8 53.6 53.0 Non-U.S. Government 6,049.0 6,049.1 490.3 496.1 — — — — 6,539.3 6,545.2 Corporate Debt 77.9 77.9 774.1 778.0 64.7 64.2 — — 916.7 920.1 Covered Bonds 1,294.1 1,300.2 1,431.9 1,445.1 320.8 319.7 — — 3,046.8 3,065.0 Certificates of Deposit 644.1 644.1 — — — — — — 644.1 644.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 1,206.4 1,212.0 2,334.3 2,358.2 1,131.9 1,112.2 — — 4,672.6 4,682.4 Other Asset-Backed 203.9 204.3 392.6 393.3 109.7 109.5 — — 706.2 707.1 Other 36.5 36.0 252.8 236.6 53.4 47.5 113.4 62.0 456.1 382.1 Total $ 9,614.9 $ 9,626.6 $ 5,684.0 $ 5,715.3 $ 1,689.7 $ 1,662.3 $ 147.8 $ 95.8 $ 17,136.4 $ 17,100.0
Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value	The following table provides information regarding debt securities available for sale with no credit losses reported that had been in a continuous unrealized loss position for less than twelve months and for twelve months or longer as of March 31, 2021 and December 31, 2020. TABLE 36: DEBT SECURITIES AVAILABLE FOR SALE IN UNREALIZED LOSS POSITION WITH NO CREDIT LOSSES REPORTED AS OF MARCH 31, 2021 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED U.S. Government $ 237.6 $ 10.7 $ — $ — $ 237.6 $ 10.7 Obligations of States and Political Subdivisions 1,456.8 52.5 — — 1,456.8 52.5 Government Sponsored Agency 5,915.6 148.5 2,096.4 11.7 8,012.0 160.2 Non-U.S. Government 274.4 6.3 — — 274.4 6.3 Corporate Debt 272.6 2.8 — — 272.6 2.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 981.3 19.4 49.9 — 1,031.2 19.4 Other Asset-Backed 1,035.7 4.5 60.0 — 1,095.7 4.5 Commercial Mortgage-Backed 120.8 1.2 7.5 0.1 128.3 1.3 Total $ 10,294.8 $ 245.9 $ 2,213.8 $ 11.8 $ 12,508.6 $ 257.7 AS OF DECEMBER 31, 2020 LESS THAN 12 MONTHS 12 MONTHS OR LONGER TOTAL (In Millions) FAIR UNREALIZED FAIR UNREALIZED FAIR UNREALIZED Obligations of States and Political Subdivisions $ 52.3 $ 0.1 $ — $ — $ 52.3 $ 0.1 Government Sponsored Agency 2,402.3 13.6 2,528.7 13.3 4,931.0 26.9 Non-U.S. Government 90.5 0.7 — — 90.5 0.7 Corporate Debt 66.6 0.1 — — 66.6 0.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 162.8 0.5 49.9 0.1 212.7 0.6 Other Asset-Backed 176.8 0.2 792.3 2.6 969.1 2.8 Commercial Mortgage-Backed 44.4 0.1 — — 44.4 0.1 Total $ 2,995.7 $ 15.3 $ 3,370.9 $ 16.0 $ 6,366.6 $ 31.3
Debt Securities, Held-to-maturity	The following tables provide the amortized cost and fair values at March 31, 2021 and December 31, 2020, and remaining maturities of debt securities held to maturity at March 31, 2021. TABLE 37: RECONCILIATION OF AMORTIZED COST TO FAIR VALUE OF DEBT SECURITIES HELD TO MATURITY MARCH 31, 2021 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR U.S Government $ 100.0 $ — $ — $ 100.0 Obligations of States and Political Subdivisions 1.0 — — 1.0 Government Sponsored Agency 53.6 0.3 0.9 53.0 Non-U.S. Government 6,539.3 6.1 0.2 6,545.2 Corporate Debt 916.7 5.0 1.6 920.1 Covered Bonds 3,046.8 19.9 1.7 3,065.0 Certificates of Deposit 644.1 — — 644.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 4,672.6 33.1 23.3 4,682.4 Other Asset-Backed 706.2 1.2 0.3 707.1 Other 456.1 1.0 75.0 382.1 Total $ 17,136.4 $ 66.6 $ 103.0 $ 17,100.0 DECEMBER 31, 2020 (In Millions) AMORTIZED GROSS UNREALIZED GAINS GROSS UNREALIZED LOSSES FAIR U.S. Government $ 90.0 $ — $ — $ 90.0 Obligations of States and Political Subdivisions 2.1 0.1 — 2.2 Government Sponsored Agency 3.0 0.3 — 3.3 Non-U.S. Government 8,336.6 7.3 0.2 8,343.7 Corporate Debt 588.0 6.5 0.1 594.4 Covered Bonds 3,184.6 24.6 0.3 3,208.9 Certificates of Deposit 807.2 — — 807.2 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,648.0 43.5 0.9 3,690.6 Other Asset-Backed 677.0 0.9 — 677.9 Other 454.6 1.1 76.5 379.2 Total $ 17,791.1 $ 84.3 $ 78.0 $ 17,797.4
Debt Securities, Held-to-maturity, Credit Quality Indicator	The following table provides the amortized cost of debt securities held to maturity by credit rating. TABLE 39: AMORTIZED COST OF DEBT SECURITIES HELD TO MATURITY BY CREDIT RATING AS OF MARCH 31, 2021 (In Millions) AAA AA A BBB NOT RATED TOTAL U.S. Government $ 100.0 $ — $ — $ — $ — $ 100.0 Obligations of States and Political Subdivisions — 1.0 — — — 1.0 Government Sponsored Agency 53.6 — — — — 53.6 Non-U.S. Government 301.0 205.1 5,760.4 272.8 — 6,539.3 Corporate Debt 75.1 396.0 445.6 — — 916.7 Covered Bonds 3,046.8 — — — — 3,046.8 Certificates of Deposit — — — — 644.1 644.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,301.2 1,339.8 31.6 — — 4,672.6 Other Asset-Backed 706.2 — — — — 706.2 Other — — — — 456.1 456.1 Total $ 7,583.9 $ 1,941.9 $ 6,237.6 $ 272.8 $ 1,100.2 $ 17,136.4 Percent of Total 44 % 11 % 36 % 2 % 7 % 100 % AS OF DECEMBER 31, 2020 (In Millions) AAA AA A BBB NOT RATED TOTAL U.S. Government $ 90.0 $ — $ — $ — $ — $ 90.0 Obligations of States and Political Subdivisions — 1.0 — 1.1 — 2.1 Government Sponsored Agency 3.0 — — — — 3.0 Non-U.S. Government 319.8 1,337.4 6,630.6 48.8 — 8,336.6 Corporate Debt 3.8 279.1 305.1 — — 588.0 Covered Bonds 3,184.6 — — — — 3,184.6 Certificates of Deposit — — — — 807.2 807.2 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,590.9 1,057.1 — — — 3,648.0 Other Asset-Backed 677.0 — — — — 677.0 Other — — — — 454.6 454.6 Total $ 6,869.1 $ 2,674.6 $ 6,935.7 $ 49.9 $ 1,261.8 $ 17,791.1 Percent of Total 39 % 15 % 39 % — % 7 % 100 %

Securities Sold Under Agreeme_2

Securities Sold Under Agreements to Repurchase (Tables)	3 Months Ended
	Mar. 31, 2021
Banking and Thrift, Other Disclosures [Abstract]
Repurchase Agreements Accounted for as Secured Borrowings	The following table provides information regarding repurchase agreements that are accounted for as secured borrowings as of March 31, 2021 and December 31, 2020. TABLE 40: REPURCHASE AGREEMENTS ACCOUNTED FOR AS SECURED BORROWINGS REMAINING CONTRACTUAL MATURITY OF THE AGREEMENTS OVERNIGHT AND CONTINUOUS ($ In Millions) MARCH 31, 2021 DECEMBER 31, 2020 U.S. Treasury and Agency Securities $ 95.6 $ 39.8 Total Borrowings 95.6 39.8 Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 23 95.6 39.8 Amounts related to agreements not included in Note 23 — —

Loans and Leases (Tables)

Loans and Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Loans and Leases	Amounts outstanding for Loans and Leases, by segment and class, are shown in the following table. TABLE 41: LOANS AND LEASES (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Commercial Commercial and Institutional $ 10,073.1 $ 10,058.3 Commercial Real Estate 3,713.9 3,558.4 Non-U.S. 1,771.2 1,345.7 Lease Financing, net 11.3 11.4 Other 278.4 288.2 Total Commercial 15,847.9 15,262.0 Personal Private Client 12,047.5 11,815.1 Residential Real Estate 6,066.9 6,035.7 Non-U.S. 336.7 597.9 Other 45.3 49.0 Total Personal 18,496.4 18,497.7 Total Loans and Leases $ 34,344.3 $ 33,759.7
Borrower Ratings	Loan and lease segment and class balances as of March 31, 2021 and December 31, 2020 are provided in the following table, segregated by borrower ratings into “1 to 3,” “4 to 5” and “6 to 9” (watch list and nonaccrual status) categories by year of origination at amortized cost basis. Loans that are held for investment are reported at the principal amount outstanding, net of unearned income. TABLE 42: CREDIT QUALITY INDICATOR AT AMORTIZED COST BASIS BY ORIGINATION YEAR March 31, 2021 TERM LOANS AND LEASES REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2021 2020 2019 2018 2017 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 334.2 $ 653.5 $ 332.8 $ 179.2 $ 103.4 $ 786.0 $ 3,597.0 $ 1.2 $ 5,987.3 4 to 5 Category 196.1 697.7 524.6 339.9 343.7 288.1 1,351.5 33.6 3,775.2 6 to 9 Category 29.9 33.4 77.9 36.7 39.5 24.9 68.3 — 310.6 Total Commercial and Institutional 560.2 1,384.6 935.3 555.8 486.6 1,099.0 5,016.8 34.8 10,073.1 Commercial Real Estate Risk Rating: 1 to 3 Category 124.7 341.5 153.4 59.8 24.3 113.5 82.6 2.8 902.6 4 to 5 Category 121.4 752.7 752.0 282.2 115.8 542.7 98.8 9.4 2,675.0 6 to 9 Category 12.1 18.2 55.2 15.5 23.9 11.4 — — 136.3 Total Commercial Real Estate 258.2 1,112.4 960.6 357.5 164.0 667.6 181.4 12.2 3,713.9 Non-U.S. Risk Rating: 1 to 3 Category 724.7 112.9 17.0 — 11.1 — 270.0 — 1,135.7 4 to 5 Category 282.1 28.0 0.7 2.1 — 85.2 129.5 1.8 529.4 6 to 9 Category 0.2 — 23.1 — — — 82.8 — 106.1 Total Non-U.S. 1,007.0 140.9 40.8 2.1 11.1 85.2 482.3 1.8 1,771.2 Lease Financing, net Risk Rating: 4 to 5 Category — — — — — 11.3 — — 11.3 Total Lease Financing, net — — — — — 11.3 — — 11.3 Other Risk Rating: 1 to 3 Category 135.8 — — — — — — — 135.8 4 to 5 Category 142.6 — — — — — — — 142.6 Total Other 278.4 — — — — — — — 278.4 Total Commercial 2,103.8 2,637.9 1,936.7 915.4 661.7 1,863.1 5,680.5 48.8 15,847.9 Personal Private Client Risk Rating: 1 to 3 Category 50.9 567.3 122.5 43.7 54.5 141.5 5,283.6 59.1 6,323.1 4 to 5 Category 229.2 535.5 595.7 115.1 64.2 100.0 3,805.1 210.6 5,655.4 6 to 9 Category 0.1 5.8 0.5 21.7 — — 39.6 1.3 69.0 Total Private Client 280.2 1,108.6 718.7 180.5 118.7 241.5 9,128.3 271.0 12,047.5 Residential Real Estate Risk Rating: 1 to 3 Category 375.1 1,440.3 247.7 25.3 99.1 771.4 143.7 — 3,102.6 4 to 5 Category 150.7 877.9 359.8 111.0 127.5 957.6 245.4 5.6 2,835.5 6 to 9 Category 0.3 14.1 8.1 0.6 0.5 82.6 22.6 — 128.8 Total Residential Real Estate 526.1 2,332.3 615.6 136.9 227.1 1,811.6 411.7 5.6 6,066.9 Non-U.S. Risk Rating: 1 to 3 Category — 9.2 32.3 — — 1.1 65.9 — 108.5 4 to 5 Category — 10.2 8.2 10.7 0.4 8.8 176.0 13.6 227.9 6 to 9 Category — — — — — 0.3 — — 0.3 Total Non-U.S. — 19.4 40.5 10.7 0.4 10.2 241.9 13.6 336.7 Other Risk Rating: 1 to 3 Category 26.8 — — — — — — — 26.8 4 to 5 Category 18.5 — — — — — — — 18.5 Total Other 45.3 — — — — — — — 45.3 Total Personal 851.6 3,460.3 1,374.8 328.1 346.2 2,063.3 9,781.9 290.2 18,496.4 Total Loans and Leases $ 2,955.4 $ 6,098.2 $ 3,311.5 $ 1,243.5 $ 1,007.9 $ 3,926.4 $ 15,462.4 $ 339.0 $ 34,344.3 December 31, 2020 TERM LOANS AND LEASES REVOLVING LOANS REVOLVING LOANS CONVERTED TO TERM LOANS (In Millions) 2020 2019 2018 2017 2016 PRIOR TOTAL Commercial Commercial and Institutional Risk Rating: 1 to 3 Category $ 663.8 $ 546.0 $ 204.6 $ 96.0 $ 396.0 $ 448.8 $ 3,742.4 $ 5.5 $ 6,103.1 4 to 5 Category 793.4 505.1 354.1 405.4 134.6 167.3 1,238.7 32.3 3,630.9 6 to 9 Category 34.3 119.8 37.3 42.8 23.0 6.0 61.1 — 324.3 Total Commercial and Institutional 1,491.5 1,170.9 596.0 544.2 553.6 622.1 5,042.2 37.8 10,058.3 Commercial Real Estate Risk Rating: 1 to 3 Category 406.3 109.2 27.6 36.5 11.8 99.4 124.3 8.7 823.8 4 to 5 Category 703.1 811.8 332.7 107.4 184.5 382.8 60.4 11.4 2,594.1 6 to 9 Category 15.3 55.2 32.0 25.8 — 12.2 — — 140.5 Total Commercial Real Estate 1,124.7 976.2 392.3 169.7 196.3 494.4 184.7 20.1 3,558.4 Non-U.S. Risk Rating: 1 to 3 Category 555.2 16.8 — 11.1 — — 78.5 — 661.6 4 to 5 Category 313.1 0.7 2.0 — — 157.9 39.2 1.8 514.7 6 to 9 Category — 23.1 — — — — 146.3 — 169.4 Total Non-U.S. 868.3 40.6 2.0 11.1 — 157.9 264.0 1.8 1,345.7 Lease Financing, net Risk Rating: 4 to 5 Category — — — — — 11.4 — — 11.4 Total Lease Financing, net — — — — — 11.4 — — 11.4 Other Risk Rating: 1 to 3 Category 81.7 — — — — — — — 81.7 4 to 5 Category 206.5 — — — — — — — 206.5 Total Other 288.2 — — — — — — — 288.2 Total Commercial 3,772.7 2,187.7 990.3 725.0 749.9 1,285.8 5,490.9 59.7 15,262.0 Personal Private Client Risk Rating: 1 to 3 Category 668.6 273.7 51.7 60.4 10.2 136.1 5,392.8 47.9 6,641.4 4 to 5 Category 492.1 479.9 117.3 60.4 77.5 77.5 3,564.7 207.3 5,076.7 6 to 9 Category 6.0 0.5 22.1 3.2 — — 63.7 1.5 97.0 Total Private Client 1,166.7 754.1 191.1 124.0 87.7 213.6 9,021.2 256.7 11,815.1 Residential Real Estate Risk Rating: 1 to 3 Category 1,554.3 317.4 42.9 109.9 205.1 627.8 152.8 1.7 3,011.9 4 to 5 Category 854.6 359.5 115.8 163.2 209.7 896.5 273.1 7.4 2,879.8 6 to 9 Category 15.3 8.3 0.7 0.5 1.9 94.8 22.5 — 144.0 Total Residential Real Estate 2,424.2 685.2 159.4 273.6 416.7 1,619.1 448.4 9.1 6,035.7 Non-U.S. Risk Rating: 1 to 3 Category 23.3 14.9 — — — 1.8 275.6 — 315.6 4 to 5 Category 12.7 26.0 11.8 0.5 0.5 7.9 217.5 5.1 282.0 6 to 9 Category — — — — — 0.3 — — 0.3 Total Non-U.S. 36.0 40.9 11.8 0.5 0.5 10.0 493.1 5.1 597.9 Other Risk Rating: 1 to 3 Category 34.6 — — — — — — — 34.6 4 to 5 Category 14.4 — — — — — — — 14.4 Total Other 49.0 — — — — — — — 49.0 Total Personal 3,675.9 1,480.2 362.3 398.1 504.9 1,842.7 9,962.7 270.9 18,497.7 Total Loans and Leases $ 7,448.6 $ 3,667.9 $ 1,352.6 $ 1,123.1 $ 1,254.8 $ 3,128.5 $ 15,453.6 $ 330.6 $ 33,759.7
Delinquency Status	The following table provides balances and delinquency status of accrual and nonaccrual loans and leases by segment and class, as well as the other real estate owned and nonaccrual asset balances, as of March 31, 2021 and December 31, 2020. TABLE 43: DELINQUENCY STATUS ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS March 31, 2021 Commercial Commercial and Institutional $ 10,024.5 $ 25.1 $ 2.2 $ — $ 10,051.8 $ 21.3 $ 10,073.1 $ 9.9 Commercial Real Estate 3,660.5 8.7 — 4.6 3,673.8 40.1 3,713.9 32.2 Non-U.S. 1,771.2 — — — 1,771.2 — 1,771.2 — Lease Financing, net 11.3 — — — 11.3 — 11.3 — Other 278.4 — — — 278.4 — 278.4 — Total Commercial 15,745.9 33.8 2.2 4.6 15,786.5 61.4 15,847.9 42.1 Personal Private Client 11,912.3 103.4 11.1 17.8 12,044.6 2.9 12,047.5 2.9 Residential Real Estate 5,976.1 28.0 1.7 1.6 6,007.4 59.5 6,066.9 51.1 Non-U.S. 336.5 0.2 — — 336.7 — 336.7 — Other 45.3 — — — 45.3 — 45.3 — Total Personal 18,270.2 131.6 12.8 19.4 18,434.0 62.4 18,496.4 54.0 Total Loans and Leases $ 34,016.1 $ 165.4 $ 15.0 $ 24.0 $ 34,220.5 $ 123.8 $ 34,344.3 $ 96.1 Other Real Estate Owned $ 1.5 Total Nonaccrual Assets $ 125.3 ACCRUAL NONACCRUAL WITH NO ALLOWANCE (In Millions) CURRENT 30 – 59 DAYS 60 – 89 DAYS 90 DAYS TOTAL ACCRUAL NONACCRUAL TOTAL LOANS December 31, 2020 Commercial Commercial and Institutional $ 9,877.0 $ 153.7 $ 1.2 $ — $ 10,031.9 $ 26.4 $ 10,058.3 $ 9.1 Commercial Real Estate 3,516.2 2.0 — — 3,518.2 40.2 3,558.4 32.3 Non-U.S. 1,345.7 — — — 1,345.7 — 1,345.7 — Lease Financing, net 11.4 — — — 11.4 — 11.4 — Other 288.2 — — — 288.2 — 288.2 — Total Commercial 15,038.5 155.7 1.2 — 15,195.4 66.6 15,262.0 41.4 Personal Private Client 11,765.4 29.1 9.9 7.8 11,812.2 2.9 11,815.1 2.9 Residential Real Estate 5,946.0 23.5 2.9 1.1 5,973.5 62.2 6,035.7 53.8 Non-U.S 596.7 1.2 — — 597.9 — 597.9 — Other 49.0 — — — 49.0 — 49.0 — Total Personal 18,357.1 53.8 12.8 8.9 18,432.6 65.1 18,497.7 56.7 Total Loans and Leases $ 33,395.6 $ 209.5 $ 14.0 $ 8.9 $ 33,628.0 $ 131.7 $ 33,759.7 $ 98.1 Other Real Estate Owned $ 0.7 Total Nonaccrual Assets $ 132.4
Modified Troubled Debt Restructurings	The following table provides, by segment and class, the number of TDR modifications of loans and leases during the three month periods ended March 31, 2021 and 2020, and the recorded investments and unpaid principal balances as of March 31, 2021 and 2020. TABLE 44: TROUBLED DEBT RESTRUCTURINGS THREE MONTHS ENDED MARCH 31, 2021 ($ In Millions) NUMBER OF RECORDED UNPAID Commercial Commercial and Institutional 6 $ 19.6 $ 19.6 Commercial Real Estate 1 21.4 23.3 Total Commercial 7 41.0 42.9 Personal Residential Real Estate 2 0.2 0.3 Total Personal 2 0.2 0.3 Total Loans and Leases 9 $ 41.2 $ 43.2 Note: Period-end balances reflect all paydowns and charge-offs during the period. THREE MONTHS ENDED MARCH 31, 2020 ($ In Millions) NUMBER OF RECORDED UNPAID Commercial Commercial and Institutional 2 $ 24.3 $ 24.5 Total Commercial 2 24.3 24.5 Personal Residential Real Estate 6 1.0 1.2 Total Personal 6 1.0 1.2 Total Loans and Leases 8 $ 25.3 $ 25.7 Note: Period-end balances reflect all paydowns and charge-offs during the period.
Schedule Of Non-Troubled Debt Restructuring Modifications	The following tables provide, by segment and class, the number of total COVID-19-related loan modifications including the loan volume and deferred principal and interest balances as of March 31, 2021, for which Northern Trust applied an exemption from TDR classification that are in active deferral (loans currently in the deferral period) or completed deferral (loans that returned to their regular payment schedule). TABLE 45: COVID-19 LOAN MODIFICATIONS NOT CONSIDERED TDRS IN ACTIVE DEFERRAL STATUS MARCH 31, 2021 ($ In Millions) NUMBER OF COVID-19 RELATED MODIFICATIONS LOAN VOLUME DEFERRED PRINCIPAL AMOUNT DEFERRED INTEREST AMOUNT Personal Residential Real Estate 25 $ 9.5 $ 0.2 $ 0.2 Total Personal 25 $ 9.5 $ 0.2 $ 0.2 Total Loans 25 $ 9.5 $ 0.2 $ 0.2 TABLE 46: COVID-19 LOAN MODIFICATIONS NOT CONSIDERED TDRS THAT HAVE COMPLETED DEFERRAL MARCH 31, 2021 ($ In Millions) NUMBER OF COVID-19 RELATED MODIFICATIONS LOAN VOLUME DEFERRED PRINCIPAL AMOUNT DEFERRED INTEREST AMOUNT Commercial Commercial and Institutional 90 $ 238.4 $ — $ 2.0 Commercial Real Estate 91 457.2 — 3.2 Total Commercial 181 $ 695.6 $ — $ 5.2 Personal Private Client 32 $ 169.8 $ — $ 1.2 Residential Real Estate 382 164.8 1.4 2.0 Total Personal 414 $ 334.6 $ 1.4 $ 3.2 Total Loans 595 $ 1,030.2 $ 1.4 $ 8.4

Allowance for Credit Losses (Ta

Allowance for Credit Losses (Tables)	3 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Allowance for Credit Loss	The following table provides information regarding changes in the total allowance for credit losses during the three months ended March 31, 2021 and 2020. TABLE 47: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES THREE MONTHS ENDED MARCH 31, 2021 (In Millions) LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT DEBT SECURITIES HELD TO MATURITY OTHER FINANCIAL ASSETS TOTAL Balance at Beginning of Period $ 190.7 $ 61.1 $ 7.3 $ 0.8 $ 259.9 Charge-Offs (0.4) — — — (0.4) Recoveries 1.3 — — — 1.3 Net Recoveries (Charge-Offs) 0.9 — — — 0.9 Provision for Credit Losses (26.2) (6.0) 1.3 0.9 (30.0) Balance at End of Period $ 165.4 $ 55.1 $ 8.6 $ 1.7 $ 230.8 THREE MONTHS ENDED MARCH 31, 2020 (In Millions) LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT DEBT SECURITIES HELD TO MATURITY OTHER FINANCIAL ASSETS TOTAL Balance at End of Prior Period $ 104.5 $ 19.9 $ — $ — $ 124.4 Cumulative Effect Adjustment (2.2) 8.9 6.6 0.4 13.7 Balance at Beginning of Period $ 102.3 $ 28.8 $ 6.6 $ 0.4 $ 138.1 Charge-Offs (1.8) — — — (1.8) Recoveries 1.1 — — — 1.1 Net Recoveries (Charge-Offs) (0.7) — — — (0.7) Provision for Credit Losses (1) 45.6 11.6 2.9 0.7 60.8 Balance at End of Period $ 147.2 $ 40.4 $ 9.5 $ 1.1 $ 198.2 (1) The table excludes $0.2 million of credit losses recognized for corporate debt securities available for sale as of March 31, 2020. See further detail in Note 4 - Securities. TABLE 48: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO LOANS AND LEASES THREE MONTHS ENDED MARCH 31, 2021 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at Beginning of Period $ 142.2 $ 48.5 $ 190.7 $ 57.6 $ 3.5 $ 61.1 Charge-Offs — (0.4) (0.4) — — — Recoveries — 1.3 1.3 — — — Net Recoveries (Charge-Offs) — 0.9 0.9 — — — Provision for Credit Losses (17.5) (8.7) (26.2) (5.9) (0.1) (6.0) Balance at End of Period $ 124.7 $ 40.7 $ 165.4 $ 51.7 $ 3.4 $ 55.1 THREE MONTHS ENDED MARCH 31, 2020 LOANS AND LEASES UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Balance at End of Prior Period $ 58.1 $ 46.4 $ 104.5 $ 15.8 $ 4.1 $ 19.9 Cumulative Effect Adjustment (5.9) 3.7 (2.2) 11.9 (3.0) 8.9 Balance at Beginning of Period $ 52.2 $ 50.1 $ 102.3 $ 27.7 $ 1.1 $ 28.8 Charge-Offs (0.1) (1.7) (1.8) — — — Recoveries 0.7 0.4 1.1 — — — Net Recoveries (Charge-Offs) 0.6 (1.3) (0.7) — — — Provision for Credit Losses 41.9 3.7 45.6 11.1 0.5 11.6 Balance at End of Period $ 94.7 $ 52.5 $ 147.2 $ 38.8 $ 1.6 $ 40.4 The following table provides information regarding the recorded investments in loans and leases and the allowance for credit losses for loans and leases and undrawn loan commitments and standby letters of credit by segment as of March 31, 2021 and December 31, 2020. TABLE 49: RECORDED INVESTMENTS IN LOANS AND LEASES MARCH 31, 2021 DECEMBER 31, 2020 (In Millions) COMMERCIAL PERSONAL TOTAL COMMERCIAL PERSONAL TOTAL Loans and Leases Evaluated on an Individual Basis $ 61.4 $ 62.4 $ 123.8 $ 66.6 $ 65.1 $ 131.7 Evaluated on a Collective Basis 15,786.5 18,434.0 34,220.5 15,195.4 18,432.6 33,628.0 Total Loans and Leases 15,847.9 18,496.4 34,344.3 15,262.0 18,497.7 33,759.7 Allowance for Credit Losses on Credit Exposures Evaluated on an Individual Basis 10.6 0.3 10.9 8.8 0.3 9.1 Evaluated on a Collective Basis 114.1 40.4 154.5 133.4 48.2 181.6 Allowance Assigned to Loans and Leases 124.7 40.7 165.4 142.2 48.5 190.7 Allowance for Undrawn Loan Commitments and Standby Letters of Credit Evaluated on an Individual Basis — — — 1.6 — 1.6 Evaluated on a Collective Basis 51.7 3.4 55.1 56.0 3.5 59.5 Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit 51.7 3.4 55.1 57.6 3.5 61.1 Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit $ 176.4 $ 44.1 $ 220.5 $ 199.8 $ 52.0 $ 251.8
Debt Securities, Held-to-maturity, Allowance for Credit Loss	The following table provides information regarding changes in the total allowance for credit losses for debt securities held to maturity during the three months ended March 31, 2021 and March 31, 2020. TABLE 50: CHANGES IN THE ALLOWANCE FOR CREDIT LOSSES RELATED TO DEBT SECURITIES HELD TO MATURITY THREE MONTHS ENDED MARCH 31, 2021 (In Millions) CORPORATE DEBT NON-U.S. GOVERNMENT SUB-SOVEREIGN, SUPERNATIONAL, AND NON-U.S. AGENCY BONDS CERTIFICATE OF DEPOSITS COVERED BONDS OTHER TOTAL Balance at Beginning of Period $ 0.8 $ 0.2 $ 1.2 $ — $ 0.1 $ 5.0 $ 7.3 Provision for Credit Losses 0.3 0.7 0.6 — — (0.3) 1.3 Balance at End of Period $ 1.1 $ 0.9 $ 1.8 $ — $ 0.1 $ 4.7 $ 8.6 THREE MONTHS ENDED MARCH 31, 2020 (In Millions) CORPORATE DEBT NON-U.S. GOVERNMENT SUB-SOVEREIGN, SUPERNATIONAL, AND NON-U.S. AGENCY BONDS CERTIFICATE OF DEPOSITS COVERED BONDS OTHER TOTAL Balance at End of Prior Period $ — $ — $ — $ — $ — $ — $ — Cumulative Effect Adjustment 0.8 0.3 0.9 — — 4.6 6.6 Balance at Beginning of Period 0.8 0.3 0.9 — — 4.6 6.6 Provision for Credit Losses 1.9 0.1 0.4 0.2 0.1 0.2 2.9 Balance at End of Period $ 2.7 $ 0.4 $ 1.3 $ 0.2 $ 0.1 $ 4.8 $ 9.5
Schedule of Accrued Liabilities	The following table provides the amount of accrued interest excluded from the amortized cost basis of the following portfolios. TABLE 51: ACCRUED INTEREST (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Loans and Leases $ 59.4 $ 55.3 Debt Securities Held to Maturity $ 19.8 $ 26.5 Available for Sale 136.1 153.6 Other Financial Assets $ 1.6 $ 1.4

Pledged and Restricted Assets (

Pledged and Restricted Assets (Tables)	3 Months Ended
	Mar. 31, 2021
Transfers and Servicing [Abstract]
Schedule of Financial Instruments Owned and Pledged as Collateral	The following table presents Northern Trust's pledged assets. TABLE 52: TYPE OF PLEDGED ASSETS (In Billions) MARCH 31, 2021 DECEMBER 31, 2020 Securities Obligations of States and Political Subdivisions $ 3.0 $ 2.9 Government Sponsored Agency and Other Securities 30.6 32.5 Loans 12.3 12.1 Total Pledged Assets $ 45.9 $ 47.5 The following table presents the available for sale debt securities pledged as collateral that are included in pledged assets. TABLE 53: FAIR VALUE OF AVAILABLE FOR SALE DEBT SECURITIES INCLUDED IN PLEDGED ASSETS SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE DERIVATIVE CONTRACTS (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 MARCH 31, 2021 DECEMBER 31, 2020 Debt Securities Available for Sale $ 93.0 $ 33.0 $ 29.3 $ 27.1
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. There was no repledged or sold collateral at March 31, 2021 or December 31, 2020. TABLE 54: ACCEPTED COLLATERAL (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Collateral that may be repledged or sold Reverse repurchase agreements $ 309.3 $ 1,179.8 Derivative contracts 8.4 0.9 Collateral that may not be repledged or sold Reverse repurchase agreements 800.0 500.0

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	3 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill by Reporting Segment	Changes by reporting segment in the carrying amount of Goodwill for the three months ended March 31, 2021, including the effect of foreign exchange rates on non-U.S. dollar denominated balances, were as follows. TABLE 55: GOODWILL (In Millions) CORPORATE & INSTITUTIONAL SERVICES WEALTH MANAGEMENT TOTAL Balance at December 31, 2020 $ 636.0 $ 71.2 $ 707.2 Foreign Exchange Rates (3.2) — (3.2) Balance at March 31, 2021 $ 632.8 $ 71.2 $ 704.0
Other Intangible Assets	The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of March 31, 2021 and December 31, 2020 were as follows. TABLE 56: OTHER INTANGIBLE ASSETS (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Gross Carrying Amount $ 210.0 $ 221.3 Less: Accumulated Amortization 106.2 108.7 Net Book Value $ 103.8 $ 112.6 TABLE 57: CAPITALIZED SOFTWARE (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Gross Carrying Amount $ 4,404.8 $ 4,337.4 Less: Accumulated Amortization 2,810.5 2,744.5 Net Book Value $ 1,594.3 $ 1,592.9

Reporting Segments (Tables)

Reporting Segments (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Results of Reporting Segments	The following table presents the earnings contributions and average assets of Northern Trust’s reporting segments for the three month periods ended March 31, 2021 and 2020. TABLE 58: RESULTS OF REPORTING SEGMENTS ($ In Millions) CORPORATE & WEALTH MANAGEMENT OTHER TOTAL CONSOLIDATED THREE MONTHS ENDED MARCH 31, 2021 2020 2021 2020 2021 2020 2021 2020 Noninterest Income Trust, Investment and Other Servicing Fees $ 620.5 $ 574.4 $ 443.2 $ 429.2 $ — $ — $ 1,063.7 $ 1,003.6 Foreign Exchange Trading Income 74.5 85.1 4.2 3.8 — — 78.7 88.9 Other Noninterest Income 60.3 41.8 44.2 42.4 (3.6) 2.9 100.9 87.1 Total Noninterest Income 755.3 701.3 491.6 475.4 (3.6) 2.9 1,243.3 1,179.6 Net Interest Income (1) 160.7 211.3 186.0 204.9 — — 346.7 416.2 Revenue (1) 916.0 912.6 677.6 680.3 (3.6) 2.9 1,590.0 1,595.8 Provision for Credit Losses (5.4) 25.7 (24.6) 35.3 — — (30.0) 61.0 Noninterest Expense 713.1 659.3 403.1 394.4 1.3 11.9 1,117.5 1,065.6 Income before Income Taxes (1) 208.3 227.6 299.1 250.6 (4.9) (9.0) 502.5 469.2 Provision for Income Taxes (1) 50.1 49.9 78.5 60.9 (1.2) (2.2) 127.4 108.6 Net Income $ 158.2 $ 177.7 $ 220.6 $ 189.7 $ (3.7) $ (6.8) $ 375.1 $ 360.6 Percentage of Consolidated Net Income 42 % 49 % 59 % 53 % (1) % (2) % 100 % 100 % Average Assets $ 120,157.7 $ 92,715.3 $ 33,098.1 $ 31,455.2 $ — $ — $ 153,255.8 $ 124,170.5 (1) Non-GAAP financial measures stated on a fully taxable equivalent basis (FTE). Total consolidated includes FTE adjustments of $6.6 million for 2021 and $8.1 million for 2020.

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive Income (Loss)	The following tables summarize the components of Accumulated Other Comprehensive Income (Loss) (AOCI) at March 31, 2021 and 2020, and changes during the three months then ended. TABLE 59: SUMMARY OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED MARCH 31, 2021 (In Millions) NET UNREALIZED GAINS (LOSSES) ON DEBT SECURITIES AVAILABLE FOR SALE (1) NET UNREALIZED (LOSSES) GAINS ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2020 $ 641.8 $ (3.2) $ 144.7 $ (355.3) $ 428.0 Net Change (369.7) (5.2) 5.0 7.8 (362.1) Balance at March 31, 2021 $ 272.1 $ (8.4) $ 149.7 $ (347.5) $ 65.9 (1) Includes net unrealized gains on debt securities transferred from available for sale to held to maturity during the period ended March 31, 2021. THREE MONTHS ENDED MARCH 31, 2020 (In Millions) NET UNREALIZED GAINS (LOSSES) ON DEBT SECURITIES AVAILABLE FOR SALE (1) NET UNREALIZED (LOSSES) GAINS ON CASH FLOW HEDGES NET FOREIGN CURRENCY ADJUSTMENT NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS TOTAL Balance at December 31, 2019 $ 114.0 $ (3.7) $ 117.8 $ (422.8) $ (194.7) Net Change 199.7 7.3 25.7 7.0 239.7 Balance at March 31, 2020 $ 313.7 $ 3.6 $ 143.5 $ (415.8) $ 45.0 (1) Includes net unrealized gains on debt securities transferred from available for sale to held to maturity during the period ended March 31, 2020.
Details of Changes in Accumulated Other Comprehensive Income (Loss)	TABLE 60: DETAILS OF CHANGES IN ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) THREE MONTHS ENDED MARCH 31, 2021 2020 (In Millions) BEFORE TAX TAX EFFECT AFTER TAX BEFORE TAX TAX EFFECT AFTER TAX Unrealized Gains (Losses) on Debt Securities Available for Sale Unrealized Gains (Losses) on Debt Securities Available for Sale $ (496.5) $ 126.8 $ (369.7) $ 266.8 $ (67.1) $ 199.7 Reclassification Adjustment for (Gains) Losses Included in Net Income (1) — — — — — — Net Change $ (496.5) $ 126.8 $ (369.7) $ 266.8 $ (67.1) $ 199.7 Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ (2.5) $ 0.7 $ (1.8) $ 13.3 $ (3.3) $ 10.0 Interest Rate Contracts — — — 0.4 (0.1) 0.3 Reclassification Adjustment for (Gains) Losses Included in Net Income (2) (4.5) 1.1 (3.4) (4.0) 1.0 (3.0) Net Change $ (7.0) $ 1.8 $ (5.2) $ 9.7 $ (2.4) $ 7.3 Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (57.3) $ 0.5 $ (56.8) $ (89.8) $ 9.6 $ (80.2) Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) (0.2) 0.1 (0.1) (0.6) 0.1 (0.5) Net Investment Hedge Gains (Losses) 82.7 (20.8) 61.9 142.7 (36.3) 106.4 Net Change $ 25.2 $ (20.2) $ 5.0 $ 52.3 $ (26.6) $ 25.7 Pension and Other Postretirement Benefit Adjustments Net Actuarial Gains $ (1.3) $ 0.3 $ (1.0) $ (1.3) $ 0.1 $ (1.2) Reclassification Adjustment for (Gains) Losses Included in Net Income (3) Amortization of Net Actuarial Loss 11.9 (2.9) 9.0 10.9 (2.6) 8.3 Amortization of Prior Service Cost (0.3) 0.1 (0.2) (0.1) — (0.1) Net Change $ 10.3 $ (2.5) $ 7.8 $ 9.5 $ (2.5) $ 7.0 Total Net Change $ (468.0) $ 105.9 $ (362.1) $ 338.3 $ (98.6) $ 239.7 (1) The before-tax reclassification adjustment out of AOCI related to the realized gains (losses) on debt securities available for sale is recorded in Investment Security Gains (Losses), net on the consolidated statements of income. (2) See Note 22 — Derivative Financial Instruments for the location of the reclassification adjustment related to cash flow hedges. (3) The before-tax reclassification adjustment out of AOCI related to pension and other postretirement benefit adjustments is recorded in Employee Benefits expense on the consolidated statements of income.

Net Income Per Common Share (Ta

Net Income Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Net Income per Common Share	The computations of net income per common share are presented in the following table. TABLE 61: NET INCOME PER COMMON SHARE THREE MONTHS ENDED MARCH 31, ($ In Millions Except Per Common Share Information) 2021 2020 Basic Net Income Per Common Share Average Number of Common Shares Outstanding 208,112,824 208,881,131 Net Income $ 375.1 $ 360.6 Less: Dividends on Preferred Stock 16.2 30.5 Net Income Applicable to Common Stock 358.9 330.1 Less: Earnings Allocated to Participating Securities 3.7 3.9 Earnings Allocated to Common Shares Outstanding 355.2 326.2 Basic Net Income Per Common Share $ 1.71 $ 1.56 Diluted Net Income Per Common Share Average Number of Common Shares Outstanding 208,112,824 208,881,131 Plus: Dilutive Effect of Share-based Compensation 833,624 935,691 Average Common and Potential Common Shares 208,946,448 209,816,822 Earnings Allocated to Common and Potential Common Shares $ 355.2 $ 326.2 Diluted Net Income Per Common Share 1.70 1.55

Revenue from Contracts with C_2

Revenue from Contracts with Clients (Tables)	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue Disaggregation	The following table presents revenues disaggregated by major revenue source. TABLE 62: REVENUE DISAGGREGATION THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Noninterest Income Trust, Investment and Other Servicing Fees Custody and Fund Administration $ 469.7 $ 417.6 Investment Management and Advisory 516.4 510.5 Securities Lending 18.3 23.5 Other 59.3 52.0 Total Trust, Investment and Other Servicing Fees $ 1,063.7 $ 1,003.6 Other Noninterest Income Foreign Exchange Trading Income $ 78.7 $ 88.9 Treasury Management Fees 11.2 11.0 Security Commissions and Trading Income 34.8 41.7 Other Operating Income 54.9 34.4 Total Other Noninterest Income $ 179.6 $ 176.0 Total Noninterest Income $ 1,243.3 $ 1,179.6
Contract Balances	The table below represents receivables balances from contracts with clients, which are included in Other Assets on the consolidated balance sheets, at March 31, 2021 and December 31, 2020. TABLE 63: CLIENT RECEIVABLES (In Millions) MARCH 31, 2021 DECEMBER 31, 2020 Trust Fees Receivable, net (1) $ 890.2 $ 819.3 Other 116.2 116.5 Total Client Receivables $ 1,006.4 $ 935.8 (1) Trust Fees Receivable is net of a $6.7 million and $7.2 million fee receivable allowance as of March 31, 2021 and December 31, 2020, respectively.

Net Interest Income (Tables)

Net Interest Income (Tables)	3 Months Ended
	Mar. 31, 2021
Banking and Thrift, Interest [Abstract]
Net Interest Income	The components of Net Interest Income were as follows: TABLE 64: NET INTEREST INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Interest Income Loans and Leases $ 172.0 $ 250.2 Securities — Taxable 173.9 241.1 — Non-Taxable (1) 0.4 0.5 Interest-Bearing Due from and Deposits with Banks (2) 2.4 12.8 Federal Reserve and Other Central Bank Deposits and Other 1.2 24.6 Total Interest Income $ 349.9 $ 529.2 Interest Expense Deposits $ (13.4) $ 60.9 Federal Funds Purchased 0.1 2.0 Securities Sold Under Agreements to Repurchase — 1.0 Other Borrowings 3.5 29.2 Senior Notes 13.7 17.9 Long-Term Debt 5.3 8.4 Floating Rate Capital Debt 0.6 1.7 Total Interest Expense $ 9.8 $ 121.1 Net Interest Income $ 340.1 $ 408.1 (1) Non-Taxable Securities represent securities that are exempt from U.S. federal income taxes. (2) 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.

Other Operating Income (Tables)

Other Operating Income (Tables)	3 Months Ended
	Mar. 31, 2021
Other Income and Expenses [Abstract]
Components of Other Operating Income	The components of Other Operating Income were as follows: TABLE 65: OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Loan Service Fees $ 15.4 $ 11.9 Banking Service Fees 12.7 11.4 Other Income 26.8 11.1 Total Other Operating Income $ 54.9 $ 34.4

Other Operating Expense (Tables

Other Operating Expense (Tables)	3 Months Ended
	Mar. 31, 2021
Other Income and Expenses [Abstract]
Summary of other operating expenses	The components of Other Operating Expense were as follows: TABLE 66: OTHER OPERATING EXPENSE THREE MONTHS ENDED MARCH 31, ($ In Millions) 2021 2020 Business Promotion $ 7.9 $ 18.8 Staff Related 6.8 (3.5) FDIC Insurance Premiums 3.6 2.5 Other Intangibles Amortization 4.3 4.1 Other Expenses 49.1 39.9 Total Other Operating Expense $ 71.7 $ 61.8

Pension and Postretirement He_2

Pension and Postretirement Health Care (Tables)	3 Months Ended
	Mar. 31, 2021
Retirement Benefits [Abstract]
Net Periodic Pension Expense (Benefit)	The following table sets forth the net periodic pension and postretirement benefit expense for Northern Trust’s U.S. Qualified Plan, Non-U.S. Pension Plans, U.S. Non-Qualified Plan, and postretirement health care plan for the three months ended March 31, 2021 and 2020. TABLE 67: NET PERIODIC PENSION EXPENSE (BENEFIT) U.S. QUALIFIED PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Service Cost $ 13.2 $ 11.8 Interest Cost 9.8 10.8 Expected Return on Plan Assets (20.1) (19.2) Amortization Net Actuarial Loss 9.4 8.8 Prior Service Cost (0.1) (0.1) Net Periodic Pension Expense $ 12.2 $ 12.1 NON-U.S. PENSION PLANS THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Service Cost $ 0.5 $ 0.5 Interest Cost 0.6 0.7 Expected Return on Plan Assets (0.6) (0.7) Settlement Expense 0.2 0.2 Amortization Net Actuarial Loss 0.3 0.3 Prior Service Cost — — Net Periodic Pension Expense $ 1.0 $ 1.0 U.S. NON-QUALIFIED PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Service Cost $ 1.3 $ 1.1 Interest Cost 0.9 1.2 Amortization Net Actuarial Loss 2.1 1.8 Prior Service Cost — — Net Periodic Pension Expense $ 4.3 $ 4.1 POSTRETIREMENT HEALTH CARE PLAN THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Service Cost $ — $ — Interest Cost 0.1 0.2 Amortization Net Actuarial (Gain) (0.1) (0.2) Prior Service Cost (0.2) — Net Periodic Postretirement Expense $ (0.2) $ —

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2021
Share-based Payment Arrangement [Abstract]
Total Compensation Expense for Share-Based Payment Arrangements	Total compensation expense for share-based payment arrangements and the associated tax impacts were as follows for the three months ended March 31, 2021 and 2020. TABLE 68: TOTAL COMPENSATION EXPENSE FOR SHARE-BASED PAYMENT ARRANGEMENTS THREE MONTHS ENDED MARCH 31, (In Millions) 2021 2020 Restricted Stock Unit Awards $ 38.4 $ 40.7 Stock Options — 0.2 Performance Stock Units 12.1 12.9 Total Share-Based Compensation Expense 50.5 53.8 Tax Benefits Recognized $ 12.7 $ 13.4

Commitment and Contingent Liabi

Commitment and Contingent Liabilities (Tables)	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Schedule of Fair Value, Off-balance Sheet Risks	The following table provides details of Northern Trust's off-balance sheet financial instruments as of March 31, 2021 and December 31, 2020. TABLE 69: SUMMARY OF OFF-BALANCE SHEET FINANCIAL INSTRUMENTS MARCH 31, 2021 DECEMBER 31, 2020 ($ In Millions) ONE YEAR AND LESS OVER ONE YEAR TOTAL ONE YEAR AND LESS OVER ONE YEAR TOTAL Undrawn Commitments to Extend Credit (1) $ 11,519.7 $ 18,016.0 $ 29,535.7 $ 11,260.5 $ 17,678.0 $ 28,938.5 Standby Letters of Credit and Financial Guarantees (2) 1,474.8 321.0 1,795.8 1,228.1 763.5 1,991.6 Commercial Letters of Credit 66.2 — 66.2 54.6 — 54.6 Custody Securities Lent with Indemnification 176,378.0 — 176,378.0 157,478.0 — 157,478.0 Total Off-Balance Sheet Financial Instruments $ 189,438.7 $ 18,337.0 $ 207,775.7 $ 170,021.2 $ 18,441.5 $ 188,462.7 (1) These amounts exclude $404.2 million and $384.7 million of commitments participated to others at March 31, 2021 and December 31, 2020, respectively. (2) These amounts include $23.8 million and $24.2 million of standby letters of credit secured by cash deposits or participated to others as of March 31, 2021 and December 31, 2020, respectively.

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Notional and Fair Value Amounts of Client-related and Trading Derivative Financial Instruments	The following table shows the notional and fair values of all derivative financial instruments as of March 31, 2021 and December 31, 2020. TABLE 70: NOTIONAL AND FAIR VALUES OF DERIVATIVE FINANCIAL INSTRUMENTS MARCH 31, 2021 DECEMBER 31, 2020 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 $ 4,513.7 $ 10.0 $ 13.7 $ 4,717.6 $ 8.2 $ 10.2 Cash Flow Hedges — — — 50.0 0.1 — Foreign Exchange Contracts Cash Flow Hedges 6,464.9 296.7 20.4 6,554.4 15.4 104.0 Net Investment Hedges 3,482.1 73.5 8.8 3,480.3 0.1 207.7 Total Derivatives Designated as Hedging under GAAP $ 14,460.7 $ 380.2 $ 42.9 $ 14,802.3 $ 23.8 $ 321.9 Derivatives Not Designated as Hedging under GAAP Non-Designated Risk Management Derivatives Foreign Exchange Contracts $ 131.0 $ 0.7 $ 0.1 $ 67.7 $ 0.1 $ 0.1 Other Financial Derivatives (3) 721.5 — 34.6 745.4 — 35.3 Total Non-Designated Risk Management Derivatives $ 852.5 $ 0.7 $ 34.7 $ 813.1 $ 0.1 $ 35.4 Client-Related and Trading Derivatives Foreign Exchange Contracts $ 309,731.3 $ 2,630.1 $ 2,513.7 $ 320,563.4 $ 4,245.1 $ 4,410.7 Interest Rate Contracts 10,702.2 195.6 110.0 10,573.3 289.2 114.8 Total Client-Related and Trading Derivatives $ 320,433.5 $ 2,825.7 $ 2,623.7 $ 331,136.7 $ 4,534.3 $ 4,525.5 Total Derivatives Not Designated as Hedging under GAAP $ 321,286.0 $ 2,826.4 $ 2,658.4 $ 331,949.8 $ 4,534.4 $ 4,560.9 Total Gross Derivatives $ 335,746.7 $ 3,206.6 $ 2,701.3 $ 346,752.1 $ 4,558.2 $ 4,882.8 Less: Netting (4) 1,977.1 2,090.3 3,507.8 2,817.1 Total Derivative Financial Instruments $ 1,229.5 $ 611.0 $ 1,050.4 $ 2,065.7 (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. (4) See further detail in Note 23 — Offsetting of Assets and Liabilities.
Cash Flow Hedge Derivative Gains and Losses Recognized in AOCI and Reclassified to Income	The following tables provide fair value and cash flow hedge derivative gains and losses recognized in income during the three-month periods ended March 31, 2021 and 2020. TABLE 71: LOCATION AND AMOUNT OF FAIR VALUE AND CASH FLOW HEDGE DERIVATIVE GAINS AND LOSSES RECORDED IN INCOME (In Millions) INTEREST INCOME INTEREST EXPENSE OTHER OPERATING INCOME THREE MONTHS ENDED MARCH 31, 2021 2020 2021 2020 2021 2020 Total amounts on the consolidated statements of income $ 349.9 $ 529.2 $ 9.8 $ 121.1 $ 54.9 $ 34.4 Gains (Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives 18.4 (76.0) (142.9) 150.4 — — Recognized on hedged items (18.4) 76.0 142.9 (150.4) — — Amounts related to interest settlements on derivatives (1.6) (0.5) 7.0 (2.9) — — Total gains (losses) recognized on fair value hedges $ (1.6) $ (0.5) $ 7.0 $ (2.9) $ — $ — Gains (Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gains (losses) reclassified from AOCI to net income $ 5.5 $ 4.1 $ — $ — $ (1.0) $ (0.1) Total gains (losses) reclassified from AOCI to net income on cash flow hedges $ 5.5 $ 4.1 $ — $ — $ (1.0) $ (0.1)
Location and Amount of Fair Value Hedge Derivative Gains and Losses Recorded in Income	The following table provides the impact of fair value hedge accounting on the carrying value of the designated hedged items as of March 31, 2021 and December 31, 2020. TABLE 72: HEDGED ITEMS IN FAIR VALUE HEDGES MARCH 31, 2021 DECEMBER 31, 2020 (In Millions) CARRYING VALUE OF THE HEDGED ITEMS CUMULATIVE HEDGE ACCOUNTING BASIS ADJUSTMENT (1) CARRYING VALUE OF THE HEDGED ITEMS CUMULATIVE HEDGE ACCOUNTING BASIS ADJUSTMENT (2) Available for Sale Debt Securities (3) $ 1,807.4 $ 35.3 $ 2,075.1 $ 48.8 Senior Notes and Long-Term Subordinated Debt 2,745.2 66.5 2,745.1 221.5 Total $ 4,552.6 $ 101.8 $ 4,820.2 $ 270.3 (1) The cumulative hedge accounting basis adjustment includes $10.2 million related to discontinued hedging relationships of available for sale debt securities as of March 31, 2021. 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 March 31, 2021. (2) The cumulative hedge accounting basis adjustment includes $10.4 million related to discontinued hedging relationships of available for sale debt securities as of December 31, 2020. 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, 2020. (3) 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 months ended March 31, 2021 and 2020 for derivative instruments not designated as hedges under GAAP. TABLE 73: LOCATION AND AMOUNT OF GAINS AND LOSSES RECORDED IN INCOME FOR DERIVATIVES NOT DESIGNATED AS HEDGING UNDER GAAP (In Millions) DERIVATIVE GAINS (LOSSES) LOCATION RECOGNIZED IN INCOME AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME THREE MONTHS ENDED MARCH 31, 2021 2020 Non-designated risk management derivatives Foreign Exchange Contracts Other Operating Income $ 0.1 $ 0.1 Other Financial Derivatives (1) Other Operating Income (3.6) 2.9 Gains (Losses) from non-designated risk management derivatives $ (3.5) $ 3.0 Client-related and trading derivatives Foreign Exchange Contracts Foreign Exchange Trading Income $ 78.7 $ 88.9 Interest Rate Contracts Security Commissions and Trading Income 3.0 11.0 Gains (Losses) from client-related and trading derivatives $ 81.7 $ 99.9 Total gains (losses) from derivatives not designated as hedging under GAAP $ 78.2 $ 102.9 (1) This line includes swaps related to the sale of certain Visa Class B common shares.

Offsetting of Assets and Liab_2

Offsetting of Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2021
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell	The following table provides information regarding the offsetting of derivative assets and securities purchased under agreements to resell within the consolidated balance sheets as of March 31, 2021 and December 31, 2020. TABLE 74: OFFSETTING OF DERIVATIVE ASSETS AND SECURITIES PURCHASED UNDER AGREEMENTS TO RESELL MARCH 31, 2021 (In Millions) GROSS RECOGNIZED ASSETS GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (2) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET NET AMOUNT (3) Derivative Assets (1) Foreign Exchange Contracts Over the Counter (OTC) $ 2,303.8 $ 1,973.5 $ 330.3 $ 8.4 $ 321.9 Interest Rate Swaps OTC 204.0 3.6 200.4 — 200.4 Interest Rate Swaps Exchange Cleared 1.6 — 1.6 — 1.6 Total Derivatives Subject to a Master Netting Arrangement 2,509.4 1,977.1 532.3 8.4 523.9 Total Derivatives Not Subject to a Master Netting Arrangement 697.2 — 697.2 — 697.2 Total Derivatives 3,206.6 1,977.1 1,229.5 8.4 1,221.1 Securities Purchased under Agreements to Resell $ 1,109.3 $ — $ 1,109.3 $ 1,109.3 $ — DECEMBER 31, 2020 (In Millions) GROSS RECOGNIZED ASSETS GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (2) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET NET AMOUNT (3) Derivative Assets (1) Foreign Exchange Contracts OTC $ 3,799.7 $ 3,505.3 $ 294.4 $ 0.9 $ 293.5 Interest Rate Swaps OTC 295.9 2.5 293.4 — 293.4 Interest Rate Swaps Exchange Cleared 1.6 — 1.6 — 1.6 Total Derivatives Subject to a Master Netting Arrangement 4,097.2 3,507.8 589.4 0.9 588.5 Total Derivatives Not Subject to a Master Netting Arrangement 461.0 — 461.0 — 461.0 Total Derivatives 4,558.2 3,507.8 1,050.4 0.9 1,049.5 Securities Purchased under Agreements to Resell $ 1,596.5 $ — $ 1,596.5 $ 1,596.5 $ — (1) Derivative assets are reported in Other Assets on the consolidated balance sheets. Other Assets (excluding derivative assets) totaled $7.6 billion and $7.3 billion as of March 31, 2021 and December 31, 2020, respectively. (2) Including cash collateral received from counterparties. (3) Northern Trust did not possess any cash collateral that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2021 and December 31, 2020.
Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase	The following table provides information regarding the offsetting of derivative liabilities and securities sold under agreements to repurchase within the consolidated balance sheets as of March 31, 2021 and December 31, 2020. TABLE 75: OFFSETTING OF DERIVATIVE LIABILITIES AND SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE MARCH 31, 2021 (In Millions) GROSS RECOGNIZED LIABILITIES GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (2) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET NET AMOUNT (3) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 2,093.4 $ 2,023.7 $ 69.7 $ 0.9 $ 68.8 Interest Rate Swaps OTC 123.7 66.6 57.1 — 57.1 Other Financial Derivatives 34.6 — 34.6 — 34.6 Total Derivatives Subject to a Master Netting Arrangement 2,251.7 2,090.3 161.4 0.9 160.5 Total Derivatives Not Subject to a Master Netting Arrangement 449.6 — 449.6 — 449.6 Total Derivatives 2,701.3 2,090.3 611.0 0.9 610.1 Securities Sold under Agreements to Repurchase $ 95.6 $ — $ 95.6 $ 95.6 $ — DECEMBER 31, 2020 (In Millions) GROSS RECOGNIZED LIABILITIES GROSS AMOUNTS OFFSET IN THE BALANCE SHEET (2) NET AMOUNTS PRESENTED IN THE BALANCE SHEET GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET NET AMOUNT (3) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 3,577.7 $ 2,718.6 $ 859.1 $ 0.5 $ 858.6 Interest Rate Swaps OTC 125.0 98.5 26.5 — 26.5 Interest Rate Swaps Exchange Cleared — — — — — Other Financial Derivatives 35.3 — 35.3 — 35.3 Total Derivatives Subject to a Master Netting Arrangement 3,738.0 2,817.1 920.9 0.5 920.4 Total Derivatives Not Subject to a Master Netting Arrangement 1,144.8 — 1,144.8 — 1,144.8 Total Derivatives 4,882.8 2,817.1 2,065.7 0.5 2,065.2 Securities Sold under Agreements to Repurchase $ 39.8 $ — $ 39.8 $ 39.8 $ — (1) Derivative liabilities are reported in Other Liabilities on the consolidated balance sheets. Other Liabilities (excluding derivative liabilities) totaled $4.4 billion and $3.5 billion as of March 31, 2021 and December 31, 2020, respectively. (2) Including cash collateral deposited with counterparties. (3) Northern Trust did not place any cash collateral with counterparties that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2021 and December 31, 2020.

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) shares in Millions, $ in Millions	Mar. 31, 2021USD ($)security	Dec. 31, 2020USD ($)security	Jun. 30, 2016shares	Jun. 30, 2015shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale	$ 42,878.6	$ 42,022
Trading account securities	$ 0.4	$ 0.5
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	2,471	2,260
Available-for-sale	$ 40,300	$ 39,200
LEVEL 2 | External Pricing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of available for sale securities portfolio | security		2,260
Trading account securities		$ 0.5
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	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	0.200
LEVEL 3 | Fair Value, Measurements, Nonrecurring | Measurement Input, Discount Rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, measurement input	0.158	0.168
LEVEL 3 | Fair Value, Measurements, Nonrecurring | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 16.7

Fair Value Measurements (Level

Fair Value Measurements (Level 3 Significant Unobservable Inputs) (Details) $ in Millions	Mar. 31, 2021USD ($)month	Dec. 31, 2020USD ($)month
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities | $	$ 611	$ 2,065.7
Swap | Fair Value, Measurements, Recurring | LEVEL 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative liabilities | $	$ 34.6	$ 35.3
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	1.62	1.62
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	0.0963	0.0873
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	20	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	33	33

Fair Value Measurements (Recurr

Fair Value Measurements (Recurring Basis Hierarchy Leveling) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	$ 42,878.6	$ 42,022
Derivative Assets	3,206.6	4,558.2
NETTING	(1,977.1)	(3,507.8)
Derivative Assets	1,229.5	1,050.4
Derivative Liabilities	2,701.3	4,882.8
NETTING	(2,090.3)	(2,817.1)
Derivative Liabilities	611	2,065.7
Cross Product Collateral Adjustment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(449.1)	(1,867.8)
NETTING	(562.3)	(1,177.2)
U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,561	2,799.9
Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	3,279.8	3,083.6
Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	24,650.7	24,956.7
Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	558.1	714
Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,398.7	2,539.6
Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	544.1	553.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	3,003.4	2,345.8
Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	4,783	3,997.5
Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,099.8	1,031.8
LEVEL 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	40,300	39,200
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	42,878.6	42,022
Trading Account	0.4	0.5
Total Available for Sale and Trading Debt Securities	42,879	42,022.5
Fair Value, Measurements, Recurring | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,561	2,799.9
Fair Value, Measurements, Recurring | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	3,279.8	3,083.6
Fair Value, Measurements, Recurring | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	24,650.7	24,956.7
Fair Value, Measurements, Recurring | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	558.1	714
Fair Value, Measurements, Recurring | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,398.7	2,539.6
Fair Value, Measurements, Recurring | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	544.1	553.1
Fair Value, Measurements, Recurring | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	3,003.4	2,345.8
Fair Value, Measurements, Recurring | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	4,783	3,997.5
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,099.8	1,031.8
Fair Value, Measurements, Recurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(1,977.1)	(3,507.8)
Derivative Assets	1,229.5	1,050.4
Fair Value, Measurements, Recurring | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(1,973.5)	(3,505.3)
Derivative Assets	1,027.5	755.4
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(3.6)	(2.5)
Derivative Assets	202	295
Fair Value, Measurements, Recurring | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(2,090.3)	(2,817.1)
Derivative Liabilities	611	2,065.7
Fair Value, Measurements, Recurring | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(2,023.7)	(2,718.6)
Derivative Liabilities	519.3	2,003.9
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	(66.6)	(98.5)
Derivative Liabilities	57.1	26.5
Fair Value, Measurements, Recurring | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
NETTING	0	0
Derivative Liabilities	34.6	35.3
Fair Value, Measurements, Recurring | LEVEL 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,561	2,799.9
Trading Account	0	0
Total Available for Sale and Trading Debt Securities	2,561	2,799.9
Fair Value, Measurements, Recurring | LEVEL 1 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,561	2,799.9
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]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 1 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | LEVEL 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	40,317.6	39,222.1
Trading Account	0.4	0.5
Total Available for Sale and Trading Debt Securities	40,318	39,222.6
Fair Value, Measurements, Recurring | LEVEL 2 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	0	0
Fair Value, Measurements, Recurring | LEVEL 2 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	3,279.8	3,083.6
Fair Value, Measurements, Recurring | LEVEL 2 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	24,650.7	24,956.7
Fair Value, Measurements, Recurring | LEVEL 2 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	558.1	714
Fair Value, Measurements, Recurring | LEVEL 2 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,398.7	2,539.6
Fair Value, Measurements, Recurring | LEVEL 2 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	544.1	553.1
Fair Value, Measurements, Recurring | LEVEL 2 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	3,003.4	2,345.8
Fair Value, Measurements, Recurring | LEVEL 2 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	4,783	3,997.5
Fair Value, Measurements, Recurring | LEVEL 2 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,099.8	1,031.8
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	3,206.6	4,558.2
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	3,001	4,260.7
Fair Value, Measurements, Recurring | LEVEL 2 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	205.6	297.5
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	2,666.7	4,847.5
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	2,543	4,722.5
Fair Value, Measurements, Recurring | LEVEL 2 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	123.7	125
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]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | LEVEL 3 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	34.6	35.3
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	$ 34.6	$ 35.3

Fair Value Measurements (Change

Fair Value Measurements (Changes in Level 3 Liabilities) (Details) - SWAPS RELATED TO SALE OF CERTAIN VISA CLASS B COMMON SHARES - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value liabilities beginning balance	$ 35.3	$ 33.4
Total (Gains) Losses:
Included in Earnings	3.6	(2.9)
Purchases, Issues, Sales, and Settlements
Settlements	(4.3)	(4)
Fair value liabilities ending balance	$ 34.6	$ 26.5

Fair Value Measurements (Nonrec

Fair Value Measurements (Nonrecurring Basis Significant Unobservable Inputs) (Details) - Fair Value, Measurements, Nonrecurring - LEVEL 3 $ in Millions	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FAIR VALUE	$ 16.7
Measurement Input, Discount Rate | Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
INPUT VALUES	0.150	0.150
Measurement Input, Discount Rate | Upper Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
INPUT VALUES	0.200	0.200
Measurement Input, Discount Rate | Weighted Average
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
INPUT VALUES	0.158	0.168
Loans | Measurement Input, Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
FAIR VALUE	$ 16.7	$ 24.6

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
ASSETS
Cash and Due from Banks	$ 4,584.4	$ 4,389.5
Federal Reserve and Other Central Bank Deposits	46,911.4	55,503.6
Interest-Bearing Deposits with Banks	5,142.8	4,372.6
Securities Purchased under Agreements to Resell	1,109.3	1,596.5
Debt Securities
Available-for-sale	42,878.6	42,022
Debt securities, held-to-maturity	17,136.4	17,791.1
Loans (excluding Leases)
Client Security Settlement Receivables	1,970.2	1,160.2
Deposits
Savings Certificates and Other Time	909.7	937.1
Non U.S. Offices Interest-Bearing	63,746.5	71,198.4
Federal Funds Purchased	0.2	260.2
Securities Sold Under Agreements to Repurchase	95.6	39.8
Other Borrowings	5,428.4	4,011.5
Senior Notes	2,991.2	3,122.4
Long-Term Debt
Floating Rate Capital Debt	277.8	277.8
Derivative Instruments
Assets	2,509.4	4,097.2
Liabilities	2,251.7	3,738
LEVEL 2
Debt Securities
Available-for-sale	40,300	39,200
BOOK VALUE
ASSETS
Cash and Due from Banks	4,584.4	4,389.5
Federal Reserve and Other Central Bank Deposits	46,911.4	55,503.6
Interest-Bearing Deposits with Banks	5,142.8	4,372.6
Federal Funds Sold	0.1
Securities Purchased under Agreements to Resell	1,109.3	1,596.5
Debt Securities
Available-for-sale	42,878.6	42,022
Debt securities, held-to-maturity	17,136.4	17,791.1
Trading Account	0.4	0.5
Loans (excluding Leases)
Held for Investment	34,168.1	33,558
Client Security Settlement Receivables	1,970.2	1,160.2
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	230	275
Community Development Investments	908.1	919.6
Employee Benefit and Deferred Compensation	230.3	215.8
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	72,801.2	71,742.5
Savings Certificates and Other Time	909.7	937.1
Non U.S. Offices Interest-Bearing	63,746.5	71,198.4
Federal Funds Purchased	0.2	260.2
Securities Sold Under Agreements to Repurchase	95.6	39.8
Other Borrowings	5,428.4	4,011.5
Senior Notes	2,991.2	3,122.4
Long-Term Debt
Subordinated Debt	1,165.9	1,189.3
Floating Rate Capital Debt	277.8	277.8
Other Liabilities
Standby Letters of Credit	18.7	22.4
Loan Commitments	76.9	77
BOOK VALUE | Asset/Liability Management | Foreign Exchange Contracts
Derivative Instruments
Assets	370.9	15.6
Liabilities	29.3	311.8
BOOK VALUE | Asset/Liability Management | Interest Rate Contracts
Derivative Instruments
Assets	10	8.3
Liabilities	13.7	10.2
BOOK VALUE | Asset/Liability Management | Other Financial Derivatives
Derivative Instruments
Liabilities	34.6	35.3
BOOK VALUE | Client-Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Assets	2,630.1	4,245.1
Liabilities	2,513.7	4,410.7
BOOK VALUE | Client-Related and Trading | Interest Rate Contracts
Derivative Instruments
Assets	195.6	289.2
Liabilities	110	114.8
TOTAL FAIR VALUE
ASSETS
Cash and Due from Banks	4,584.4	4,389.5
Federal Reserve and Other Central Bank Deposits	46,911.4	55,503.6
Interest-Bearing Deposits with Banks	5,142.8	4,372.6
Federal Funds Sold	0.1
Securities Purchased under Agreements to Resell	1,109.3	1,596.5
Debt Securities
Available-for-sale	42,878.6	42,022
Debt securities, held-to-maturity	17,100	17,797.4
Trading Account	0.4	0.5
Loans (excluding Leases)
Held for Investment	34,181.7	34,017.5
Client Security Settlement Receivables	1,970.2	1,160.2
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	230	275
Community Development Investments	908.1	919.6
Employee Benefit and Deferred Compensation	234.5	228.9
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	72,801.2	71,742.5
Savings Certificates and Other Time	911	943
Non U.S. Offices Interest-Bearing	63,746.5	71,198.4
Federal Funds Purchased	0.2	260.2
Securities Sold Under Agreements to Repurchase	95.6	39.8
Other Borrowings	5,428.6	4,012.7
Senior Notes	3,083.9	3,222.6
Long-Term Debt
Subordinated Debt	1,211.5	1,250.1
Floating Rate Capital Debt	268.7	264.6
Other Liabilities
Standby Letters of Credit	18.7	22.4
Loan Commitments	76.9	77
TOTAL FAIR VALUE | Asset/Liability Management | Foreign Exchange Contracts
Derivative Instruments
Assets	370.9	15.6
Liabilities	29.3	311.8
TOTAL FAIR VALUE | Asset/Liability Management | Interest Rate Contracts
Derivative Instruments
Assets	10	8.3
Liabilities	13.7	10.2
TOTAL FAIR VALUE | Asset/Liability Management | Other Financial Derivatives
Derivative Instruments
Liabilities	34.6	35.3
TOTAL FAIR VALUE | Client-Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Assets	2,630.1	4,245.1
Liabilities	2,513.7	4,410.7
TOTAL FAIR VALUE | Client-Related and Trading | Interest Rate Contracts
Derivative Instruments
Assets	195.6	289.2
Liabilities	110	114.8
TOTAL FAIR VALUE | LEVEL 1
ASSETS
Cash and Due from Banks	4,584.4	4,389.5
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
Available-for-sale	2,561	2,799.9
Debt securities, held-to-maturity	100	90
Trading Account	0	0
Loans (excluding Leases)
Held for Investment	0	0
Client Security Settlement Receivables	0	0
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	0	0
Community Development Investments	0	0
Employee Benefit and Deferred Compensation	133.9	138.6
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	72,801.2	71,742.5
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
Subordinated Debt	0	0
Floating Rate Capital Debt	0	0
Other Liabilities
Standby Letters of Credit	0	0
Loan Commitments	0	0
TOTAL FAIR VALUE | LEVEL 1 | Asset/Liability Management | Foreign Exchange Contracts
Derivative Instruments
Assets	0	0
Liabilities	0	0
TOTAL FAIR VALUE | LEVEL 1 | Asset/Liability Management | Interest Rate Contracts
Derivative Instruments
Assets	0	0
Liabilities	0	0
TOTAL FAIR VALUE | LEVEL 1 | Asset/Liability Management | Other Financial Derivatives
Derivative Instruments
Liabilities	0	0
TOTAL FAIR VALUE | LEVEL 1 | Client-Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Assets	0	0
Liabilities	0	0
TOTAL FAIR VALUE | LEVEL 1 | Client-Related and Trading | Interest Rate Contracts
Derivative Instruments
Assets	0	0
Liabilities	0	0
TOTAL FAIR VALUE | LEVEL 2
ASSETS
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	46,911.4	55,503.6
Interest-Bearing Deposits with Banks	5,142.8	4,372.6
Federal Funds Sold	0.1
Securities Purchased under Agreements to Resell	1,109.3	1,596.5
Debt Securities
Available-for-sale	40,317.6	39,222.1
Debt securities, held-to-maturity	17,000	17,707.4
Trading Account	0.4	0.5
Loans (excluding Leases)
Held for Investment	0	0
Client Security Settlement Receivables	1,970.2	1,160.2
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	230	275
Community Development Investments	908.1	919.6
Employee Benefit and Deferred Compensation	100.6	90.3
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0	0
Savings Certificates and Other Time	911	943
Non U.S. Offices Interest-Bearing	63,746.5	71,198.4
Federal Funds Purchased	0.2	260.2
Securities Sold Under Agreements to Repurchase	95.6	39.8
Other Borrowings	5,428.6	4,012.7
Senior Notes	3,083.9	3,222.6
Long-Term Debt
Subordinated Debt	1,211.5	1,250.1
Floating Rate Capital Debt	268.7	264.6
Other Liabilities
Standby Letters of Credit	0	0
Loan Commitments	0	0
TOTAL FAIR VALUE | LEVEL 2 | Asset/Liability Management | Foreign Exchange Contracts
Derivative Instruments
Assets	370.9	15.6
Liabilities	29.3	311.8
TOTAL FAIR VALUE | LEVEL 2 | Asset/Liability Management | Interest Rate Contracts
Derivative Instruments
Assets	10	8.3
Liabilities	13.7	10.2
TOTAL FAIR VALUE | LEVEL 2 | Asset/Liability Management | Other Financial Derivatives
Derivative Instruments
Liabilities	0	0
TOTAL FAIR VALUE | LEVEL 2 | Client-Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Assets	2,630.1	4,245.1
Liabilities	2,513.7	4,410.7
TOTAL FAIR VALUE | LEVEL 2 | Client-Related and Trading | Interest Rate Contracts
Derivative Instruments
Assets	195.6	289.2
Liabilities	110	114.8
TOTAL 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
Available-for-sale	0	0
Debt securities, held-to-maturity	0	0
Trading Account	0	0
Loans (excluding Leases)
Held for Investment	34,181.7	34,017.5
Client Security Settlement Receivables	0	0
Other Assets
Federal Reserve and Federal Home Loan Bank Stock	0	0
Community Development Investments	0	0
Employee Benefit and Deferred Compensation	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
Subordinated Debt	0	0
Floating Rate Capital Debt	0	0
Other Liabilities
Standby Letters of Credit	18.7	22.4
Loan Commitments	76.9	77
TOTAL FAIR VALUE | LEVEL 3 | Asset/Liability Management | Foreign Exchange Contracts
Derivative Instruments
Assets	0	0
Liabilities	0	0
TOTAL FAIR VALUE | LEVEL 3 | Asset/Liability Management | Interest Rate Contracts
Derivative Instruments
Assets	0	0
Liabilities	0	0
TOTAL FAIR VALUE | LEVEL 3 | Asset/Liability Management | Other Financial Derivatives
Derivative Instruments
Liabilities	34.6	35.3
TOTAL FAIR VALUE | LEVEL 3 | Client-Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Assets	0	0
Liabilities	0	0
TOTAL FAIR VALUE | LEVEL 3 | Client-Related and Trading | Interest Rate Contracts
Derivative Instruments
Assets	0	0
Liabilities	$ 0	$ 0

Securities (Reconciliation of A

Securities (Reconciliation of Amortized Cost to Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Investment Holdings [Line Items]
Total	$ 42,508.6	$ 41,155.7
GROSS UNREALIZED GAINS	627.7	897.6
GROSS UNREALIZED LOSSES	257.7	31.3
FAIR VALUE	42,878.6	42,022
U.S. Government
Investment Holdings [Line Items]
Total	2,521.1	2,728.8
GROSS UNREALIZED GAINS	50.6	71.1
GROSS UNREALIZED LOSSES	10.7	0
FAIR VALUE	2,561	2,799.9
Obligations of States and Political Subdivisions
Investment Holdings [Line Items]
Total	3,249.8	2,927.8
GROSS UNREALIZED GAINS	82.5	155.9
GROSS UNREALIZED LOSSES	52.5	0.1
FAIR VALUE	3,279.8	3,083.6
Government Sponsored Agency
Investment Holdings [Line Items]
Total	24,535.5	24,595.1
GROSS UNREALIZED GAINS	275.4	388.5
GROSS UNREALIZED LOSSES	160.2	26.9
FAIR VALUE	24,650.7	24,956.7
Non-U.S. Government
Investment Holdings [Line Items]
Total	564.3	713.6
GROSS UNREALIZED GAINS	0.1	1.1
GROSS UNREALIZED LOSSES	6.3	0.7
FAIR VALUE	558.1	714
Corporate Debt
Investment Holdings [Line Items]
Total	2,336.3	2,459.9
GROSS UNREALIZED GAINS	65.2	79.8
GROSS UNREALIZED LOSSES	2.8	0.1
FAIR VALUE	2,398.7	2,539.6
Covered Bonds
Investment Holdings [Line Items]
Total	535.8	543.1
GROSS UNREALIZED GAINS	8.3	10
GROSS UNREALIZED LOSSES	0	0
FAIR VALUE	544.1	553.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Investment Holdings [Line Items]
Total	2,968.8	2,281.7
GROSS UNREALIZED GAINS	54	64.7
GROSS UNREALIZED LOSSES	19.4	0.6
FAIR VALUE	3,003.4	2,345.8
Other Asset-Backed
Investment Holdings [Line Items]
Total	4,749.5	3,953.5
GROSS UNREALIZED GAINS	38	46.8
GROSS UNREALIZED LOSSES	4.5	2.8
FAIR VALUE	4,783	3,997.5
Commercial Mortgage-Backed
Investment Holdings [Line Items]
Total	1,047.5	952.2
GROSS UNREALIZED GAINS	53.6	79.7
GROSS UNREALIZED LOSSES	1.3	0.1
FAIR VALUE	$ 1,099.8	$ 1,031.8

Securities (Remaining Maturity

Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Available for Sale - Cost
Due in One Year or Less	$ 7,001.8
Due After One Year Through Five Years	18,562.6
Due After Five Years Through Ten Years	14,092
Due After Ten Years	2,852.2
Total	42,508.6	$ 41,155.7
Available for Sale - Value
Due in One Year or Less	7,073.4
Due After One Year Through Five Years	18,840.3
Due After Five Years Through Ten Years	14,111.8
Due After Ten Years	2,853.1
Total	42,878.6	42,022
Held to Maturity - Amortized Cost
Due in One Year or Less	9,614.9
Due After One Year Through Five Years	5,684
Due After Five Years Through Ten Years	1,689.7
Due After Ten Years	147.8
Total	17,136.4	17,791.1
Held to Maturity - Fair Value
Due in One Year or Less	9,626.6
Due After One Year Through Five Years	5,715.3
Due After Five Years Through Ten Years	1,662.3
Due After Ten Years	95.8
Total	17,100	17,797.4
U.S. Government
Available for Sale - Cost
Due in One Year or Less	99.9
Due After One Year Through Five Years	1,874.1
Due After Five Years Through Ten Years	547.1
Due After Ten Years	0
Total	2,521.1	2,728.8
Available for Sale - Value
Due in One Year or Less	101.5
Due After One Year Through Five Years	1,911.3
Due After Five Years Through Ten Years	548.2
Due After Ten Years	0
Total	2,561	2,799.9
Held to Maturity - Amortized Cost
Due in One Year or Less	100
Due After One Year Through Five Years	0
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	100	90
Held to Maturity - Fair Value
Due in One Year or Less	100
Due After One Year Through Five Years	0
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	100	90
Obligations of States and Political Subdivisions
Available for Sale - Cost
Due in One Year or Less	7.2
Due After One Year Through Five Years	294.8
Due After Five Years Through Ten Years	2,764.2
Due After Ten Years	183.6
Total	3,249.8	2,927.8
Available for Sale - Value
Due in One Year or Less	7.3
Due After One Year Through Five Years	308.4
Due After Five Years Through Ten Years	2,787.5
Due After Ten Years	176.6
Total	3,279.8	3,083.6
Held to Maturity - Amortized Cost
Due in One Year or Less	1
Due After One Year Through Five Years	0
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	1	2.1
Held to Maturity - Fair Value
Due in One Year or Less	1
Due After One Year Through Five Years	0
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	1	2.2
Government Sponsored Agency
Available for Sale - Cost
Due in One Year or Less	4,859.6
Due After One Year Through Five Years	8,260.4
Due After Five Years Through Ten Years	8,833.7
Due After Ten Years	2,581.8
Total	24,535.5	24,595.1
Available for Sale - Value
Due in One Year or Less	4,913.7
Due After One Year Through Five Years	8,330.3
Due After Five Years Through Ten Years	8,816.8
Due After Ten Years	2,589.9
Total	24,650.7	24,956.7
Held to Maturity - Amortized Cost
Due in One Year or Less	2
Due After One Year Through Five Years	8
Due After Five Years Through Ten Years	9.2
Due After Ten Years	34.4
Total	53.6	3
Held to Maturity - Fair Value
Due in One Year or Less	2
Due After One Year Through Five Years	8
Due After Five Years Through Ten Years	9.2
Due After Ten Years	33.8
Total	53	3.3
Non-U.S. Government
Available for Sale - Cost
Due in One Year or Less	269.6
Due After One Year Through Five Years	40.5
Due After Five Years Through Ten Years	254.2
Due After Ten Years	0
Total	564.3
Available for Sale - Value
Due in One Year or Less	269.6
Due After One Year Through Five Years	40.5
Due After Five Years Through Ten Years	248
Due After Ten Years	0
Total	558.1
Held to Maturity - Amortized Cost
Due in One Year or Less	6,049
Due After One Year Through Five Years	490.3
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	6,539.3	8,336.6
Held to Maturity - Fair Value
Due in One Year or Less	6,049.1
Due After One Year Through Five Years	496.1
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	6,545.2	8,343.7
Corporate Debt
Available for Sale - Cost
Due in One Year or Less	372.6
Due After One Year Through Five Years	1,950.5
Due After Five Years Through Ten Years	9.3
Due After Ten Years	3.9
Total	2,336.3	2,459.9
Available for Sale - Value
Due in One Year or Less	376.5
Due After One Year Through Five Years	2,009.1
Due After Five Years Through Ten Years	9.2
Due After Ten Years	3.9
Total	2,398.7	2,539.6
Held to Maturity - Amortized Cost
Due in One Year or Less	77.9
Due After One Year Through Five Years	774.1
Due After Five Years Through Ten Years	64.7
Due After Ten Years	0
Total	916.7	588
Held to Maturity - Fair Value
Due in One Year or Less	77.9
Due After One Year Through Five Years	778
Due After Five Years Through Ten Years	64.2
Due After Ten Years	0
Total	920.1	594.4
Covered Bonds
Available for Sale - Cost
Due in One Year or Less	106.8
Due After One Year Through Five Years	429
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	535.8	543.1
Available for Sale - Value
Due in One Year or Less	107.1
Due After One Year Through Five Years	437
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	544.1	553.1
Held to Maturity - Amortized Cost
Due in One Year or Less	1,294.1
Due After One Year Through Five Years	1,431.9
Due After Five Years Through Ten Years	320.8
Due After Ten Years	0
Total	3,046.8	3,184.6
Held to Maturity - Fair Value
Due in One Year or Less	1,300.2
Due After One Year Through Five Years	1,445.1
Due After Five Years Through Ten Years	319.7
Due After Ten Years	0
Total	3,065	3,208.9
Certificates of Deposit
Held to Maturity - Amortized Cost
Due in One Year or Less	644.1
Due After One Year Through Five Years	0
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	644.1	807.2
Held to Maturity - Fair Value
Due in One Year or Less	644.1
Due After One Year Through Five Years	0
Due After Five Years Through Ten Years	0
Due After Ten Years	0
Total	644.1	807.2
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Cost
Due in One Year or Less	534.4
Due After One Year Through Five Years	2,001.7
Due After Five Years Through Ten Years	432.7
Due After Ten Years	0
Total	2,968.8	2,281.7
Available for Sale - Value
Due in One Year or Less	537.5
Due After One Year Through Five Years	2,043
Due After Five Years Through Ten Years	422.9
Due After Ten Years	0
Total	3,003.4	2,345.8
Held to Maturity - Amortized Cost
Due in One Year or Less	1,206.4
Due After One Year Through Five Years	2,334.3
Due After Five Years Through Ten Years	1,131.9
Due After Ten Years	0
Total	4,672.6	3,648
Held to Maturity - Fair Value
Due in One Year or Less	1,212
Due After One Year Through Five Years	2,358.2
Due After Five Years Through Ten Years	1,112.2
Due After Ten Years	0
Total	4,682.4	3,690.6
Other Asset-Backed
Available for Sale - Cost
Due in One Year or Less	733.9
Due After One Year Through Five Years	3,201.6
Due After Five Years Through Ten Years	739.2
Due After Ten Years	74.8
Total	4,749.5	3,953.5
Available for Sale - Value
Due in One Year or Less	742.4
Due After One Year Through Five Years	3,228.2
Due After Five Years Through Ten Years	737.8
Due After Ten Years	74.6
Total	4,783	3,997.5
Held to Maturity - Amortized Cost
Due in One Year or Less	203.9
Due After One Year Through Five Years	392.6
Due After Five Years Through Ten Years	109.7
Due After Ten Years	0
Total	706.2	677
Held to Maturity - Fair Value
Due in One Year or Less	204.3
Due After One Year Through Five Years	393.3
Due After Five Years Through Ten Years	109.5
Due After Ten Years	0
Total	707.1	677.9
Other
Held to Maturity - Amortized Cost
Due in One Year or Less	36.5
Due After One Year Through Five Years	252.8
Due After Five Years Through Ten Years	53.4
Due After Ten Years	113.4
Total	456.1	454.6
Held to Maturity - Fair Value
Due in One Year or Less	36
Due After One Year Through Five Years	236.6
Due After Five Years Through Ten Years	47.5
Due After Ten Years	62
Total	382.1	379.2
Commercial Mortgage-Backed
Available for Sale - Cost
Due in One Year or Less	17.8
Due After One Year Through Five Years	510
Due After Five Years Through Ten Years	511.6
Due After Ten Years	8.1
Total	1,047.5	952.2
Available for Sale - Value
Due in One Year or Less	17.8
Due After One Year Through Five Years	532.5
Due After Five Years Through Ten Years	541.4
Due After Ten Years	8.1
Total	$ 1,099.8	$ 1,031.8

Securities (Securities with Unr

Securities (Securities with Unrealized Losses) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Fair Value
Less than 12 months, fair value	$ 10,294.8	$ 2,995.7
12 months or longer fair value	2,213.8	3,370.9
Total fair value	12,508.6	6,366.6
Unrealized Losses
Less than 12 months, unrealized losses	245.9	15.3
12 months or longer unrealized losses	11.8	16
Total unrealized losses	257.7	31.3
U.S. Government
Fair Value
Less than 12 months, fair value	237.6
12 months or longer fair value	0
Total fair value	237.6
Unrealized Losses
Less than 12 months, unrealized losses	10.7
12 months or longer unrealized losses	0
Total unrealized losses	10.7
Obligations of States and Political Subdivisions
Fair Value
Less than 12 months, fair value	1,456.8	52.3
12 months or longer fair value	0	0
Total fair value	1,456.8	52.3
Unrealized Losses
Less than 12 months, unrealized losses	52.5	0.1
12 months or longer unrealized losses	0	0
Total unrealized losses	52.5	0.1
Government Sponsored Agency
Fair Value
Less than 12 months, fair value	5,915.6	2,402.3
12 months or longer fair value	2,096.4	2,528.7
Total fair value	8,012	4,931
Unrealized Losses
Less than 12 months, unrealized losses	148.5	13.6
12 months or longer unrealized losses	11.7	13.3
Total unrealized losses	160.2	26.9
Non-U.S. Government
Fair Value
Less than 12 months, fair value	274.4	90.5
12 months or longer fair value	0	0
Total fair value	274.4	90.5
Unrealized Losses
Less than 12 months, unrealized losses	6.3	0.7
12 months or longer unrealized losses	0	0
Total unrealized losses	6.3	0.7
Corporate Debt
Fair Value
Less than 12 months, fair value	272.6	66.6
12 months or longer fair value	0	0
Total fair value	272.6	66.6
Unrealized Losses
Less than 12 months, unrealized losses	2.8	0.1
12 months or longer unrealized losses	0	0
Total unrealized losses	2.8	0.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value
Less than 12 months, fair value	981.3	162.8
12 months or longer fair value	49.9	49.9
Total fair value	1,031.2	212.7
Unrealized Losses
Less than 12 months, unrealized losses	19.4	0.5
12 months or longer unrealized losses	0	0.1
Total unrealized losses	19.4	0.6
Other Asset-Backed
Fair Value
Less than 12 months, fair value	1,035.7	176.8
12 months or longer fair value	60	792.3
Total fair value	1,095.7	969.1
Unrealized Losses
Less than 12 months, unrealized losses	4.5	0.2
12 months or longer unrealized losses	0	2.6
Total unrealized losses	4.5	2.8
Commercial Mortgage-Backed
Fair Value
Less than 12 months, fair value	120.8	44.4
12 months or longer fair value	7.5	0
Total fair value	128.3	44.4
Unrealized Losses
Less than 12 months, unrealized losses	1.2	0.1
12 months or longer unrealized losses	0.1	0
Total unrealized losses	$ 1.3	$ 0.1

Securities (Narrative) (Details

Securities (Narrative) (Details)	3 Months Ended
	Mar. 31, 2021USD ($)investment	Mar. 31, 2020USD ($)	Dec. 31, 2020USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Number of securities in an unrealized loss position | investment	991
Total fair value	$ 12,500,000,000
Total unrealized losses	257,700,000
Debt securities, unrealized losses	257,700,000		$ 31,300,000
Provision for credit losses	(30,000,000)	$ 60,800,000
Debt securities, held-to-maturity	17,136,400,000		$ 17,791,100,000
Debt securities, held-to-maturity, unrealized loss position, fair value	75,000,000
Held to maturity securities, transferred from available for sale	$ 0	0
Percentage of debt securities, held-to-maturity, portfolio	1		1
Gross proceeds from sale of securities	$ 0	280,000,000
Debt securities, available-for-sale, realized gain		700,000
Debt securities, available-for-sale, realized loss		700,000
Realized investment gains (losses)	$ 0
Moodys And Standard Poors A Or Higher Rating
Debt and Equity Securities, FV-NI [Line Items]
Percentage of debt securities, held-to-maturity, portfolio	0.91		0.93
BBB
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	$ 272,800,000		$ 49,900,000
Percentage of debt securities, held-to-maturity, portfolio	0.02		0
NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	$ 1,100,200,000		$ 1,261,800,000
Percentage of debt securities, held-to-maturity, portfolio	0.07		0.07
Government Sponsored Agency
Debt and Equity Securities, FV-NI [Line Items]
Total unrealized losses	$ 160,200,000
Debt securities, unrealized losses	160,200,000		$ 26,900,000
Debt securities, held-to-maturity	53,600,000		3,000,000
Government Sponsored Agency | BBB
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	0		0
Government Sponsored Agency | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	0		0
Other Asset-Backed
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses	4,500,000		2,800,000
Debt securities, held-to-maturity	706,200,000		677,000,000
Other Asset-Backed | BBB
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	0		0
Other Asset-Backed | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	0		0
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses	$ 2,800,000		100,000
Percent of corporate debt portfolio	17.00%
Provision for credit losses	$ 0	$ 200,000
Debt securities, available-for-sale, allowance for credit loss	0		0
Debt securities, held-to-maturity	916,700,000		588,000,000
Corporate Debt | BBB
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	0		0
Corporate Debt | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	0		0
Other
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	456,100,000		454,600,000
Other | BBB
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	0		0
Other | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	456,100,000		454,600,000
U.S. Government
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, unrealized losses	10,700,000
Debt securities, held-to-maturity	100,000,000		90,000,000
U.S. Government | BBB
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	0		0
U.S. Government | NOT RATED
Debt and Equity Securities, FV-NI [Line Items]
Debt securities, held-to-maturity	$ 0		$ 0

Securities (Reconciliation of_2

Securities (Reconciliation of Amortized Cost to Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule of Held-to-maturity Securities [Line Items]
Total	$ 17,136.4	$ 17,791.1
Gross Unrealized Gains	66.6	84.3
Gross Unrealized Losses	103	78
Fair Value	17,100	17,797.4
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Total	100	90
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	100	90
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Total	1	2.1
Gross Unrealized Gains	0	0.1
Gross Unrealized Losses	0	0
Fair Value	1	2.2
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Total	53.6	3
Gross Unrealized Gains	0.3	0.3
Gross Unrealized Losses	0.9	0
Fair Value	53	3.3
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Total	6,539.3	8,336.6
Gross Unrealized Gains	6.1	7.3
Gross Unrealized Losses	0.2	0.2
Fair Value	6,545.2	8,343.7
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Total	916.7	588
Gross Unrealized Gains	5	6.5
Gross Unrealized Losses	1.6	0.1
Fair Value	920.1	594.4
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Total	3,046.8	3,184.6
Gross Unrealized Gains	19.9	24.6
Gross Unrealized Losses	1.7	0.3
Fair Value	3,065	3,208.9
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Total	644.1	807.2
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	644.1	807.2
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Total	4,672.6	3,648
Gross Unrealized Gains	33.1	43.5
Gross Unrealized Losses	23.3	0.9
Fair Value	4,682.4	3,690.6
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Total	706.2	677
Gross Unrealized Gains	1.2	0.9
Gross Unrealized Losses	0.3	0
Fair Value	707.1	677.9
Other
Schedule of Held-to-maturity Securities [Line Items]
Total	456.1	454.6
Gross Unrealized Gains	1	1.1
Gross Unrealized Losses	75	76.5
Fair Value	$ 382.1	$ 379.2

Securities (Credit Quality Indi

Securities (Credit Quality Indicators) (Details) $ in Millions	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	$ 17,136.4	$ 17,791.1
Percent of Total	1	1
AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	$ 7,583.9	$ 6,869.1
Percent of Total	0.44	0.39
AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	$ 1,941.9	$ 2,674.6
Percent of Total	0.11	0.15
A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	$ 6,237.6	$ 6,935.7
Percent of Total	0.36	0.39
BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	$ 272.8	$ 49.9
Percent of Total	0.02	0
NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	$ 1,100.2	$ 1,261.8
Percent of Total	0.07	0.07
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	$ 100	$ 90
U.S. Government | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	100	90
U.S. Government | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
U.S. Government | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
U.S. Government | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
U.S. Government | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	1	2.1
Obligations of States and Political Subdivisions | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Obligations of States and Political Subdivisions | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	1	1
Obligations of States and Political Subdivisions | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Obligations of States and Political Subdivisions | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	1.1
Obligations of States and Political Subdivisions | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	53.6	3
Government Sponsored Agency | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	53.6	3
Government Sponsored Agency | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Government Sponsored Agency | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Government Sponsored Agency | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Government Sponsored Agency | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	6,539.3	8,336.6
Non-U.S. Government | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	301	319.8
Non-U.S. Government | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	205.1	1,337.4
Non-U.S. Government | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	5,760.4	6,630.6
Non-U.S. Government | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	272.8	48.8
Non-U.S. Government | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	916.7	588
Corporate Debt | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	75.1	3.8
Corporate Debt | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	396	279.1
Corporate Debt | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	445.6	305.1
Corporate Debt | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Corporate Debt | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	3,046.8	3,184.6
Covered Bonds | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	3,046.8	3,184.6
Covered Bonds | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Covered Bonds | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Covered Bonds | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Covered Bonds | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	644.1	807.2
Certificates of Deposit | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Certificates of Deposit | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Certificates of Deposit | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Certificates of Deposit | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Certificates of Deposit | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	644.1	807.2
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	4,672.6	3,648
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	3,301.2	2,590.9
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	1,339.8	1,057.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	31.6	0
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	706.2	677
Other Asset-Backed | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	706.2	677
Other Asset-Backed | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Other Asset-Backed | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Other Asset-Backed | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Other Asset-Backed | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Other
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	456.1	454.6
Other | AAA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Other | AA
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Other | A
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Other | BBB
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	0	0
Other | NOT RATED
Schedule of Held-to-maturity Securities [Line Items]
Debt securities, held-to-maturity	$ 456.1	$ 454.6

Securities Sold Under Agreeme_3

Securities Sold Under Agreements to Repurchase (Repurchase Agreements Accounted for as Secured Borrowings) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 23	$ 160.5	$ 920.4
OVERNIGHT AND CONTINUOUS
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	95.6	39.8
Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 23	95.6	39.8
Amounts related to agreements not included in Note 23	0	0
OVERNIGHT AND CONTINUOUS | U.S. Treasury and Agency Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	$ 95.6	$ 39.8

Loans and Leases (Loans and Lea

Loans and Leases (Loans and Leases) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	$ 34,344.3	$ 33,759.7
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	15,847.9	15,262
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	10,073.1	10,058.3
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	3,713.9	3,558.4
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	1,771.2	1,345.7
Commercial | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	11.3	11.4
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	278.4	288.2
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	18,496.4	18,497.7
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	12,047.5	11,815.1
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	6,066.9	6,035.7
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	336.7	597.9
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL LOANS AND LEASES	$ 45.3	$ 49

Loans and Leases (Narrative) (D

Loans and Leases (Narrative) (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2021USD ($)contractloan	Mar. 31, 2020USD ($)	Dec. 31, 2019loan	Dec. 31, 2020USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 34,344,300,000			$ 33,759,700,000
Other U.S. loans and non-U.S. loans, short duration advances	1,300,000,000			1,100,000,000
Demand deposits	5,600,000			26,400,000
Financing receivable, nonaccrual, interest income	900,000	$ 1,300,000
Financing receivable, nonaccrual troubled debt restructuring	78,800,000			38,900,000
Financing receivable, recorded investment	23,300,000			29,300,000
Financing receivable, troubled debt restructuring, commitment to lend	8,900,000			10,400,000
Foreclosed real estate properties, carrying value	1,500,000			700,000
Loans in process of foreclosure	$ 6,500,000
CARES Act
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, number of contracts paid off | contract	38
Financing receivable, non-TDR modifications, recorded investment paid off	$ 42,900,000
Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans approved for forgiveness | loan	219
Loans approved and fully forgiven	$ 34,200,000
Loan processing fee	$ 2,600,000
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, troubled debt restructuring, subsequent default, number of contracts | loan	1		0
Impaired financing receivable, recorded investment	$ 5,500,000
Impaired financing receivable, unpaid principal balance	5,500,000
Lease Agreements
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale	0			0
Mortgages
Accounts, Notes, Loans and Financing Receivable [Line Items]
Held for sale	0			0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 18,496,400,000			18,497,700,000
Personal | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on Residential real estate loan, lower limit	65.00%
Collateral required on Residential real estate loan, upper limit	80.00%
Loans and leases	$ 6,066,900,000			6,035,700,000
Personal | Home Equity Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Draw period for credit line products	10 years
Loans and leases	$ 285,200,000			$ 304,400,000
Percentage of total equity credit lines	97.00%			97.00%
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 15,847,900,000			$ 15,262,000,000
Commercial | Commercial and Institutional
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	10,073,100,000			$ 10,058,300,000
Commercial | Commercial and Institutional | Paycheck Protection Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and leases	$ 213,900,000
Number of contracts | loan	1,137,000,000
Financing receivable, average balance per loan	$ 200,000

Loans and Leases (Credit Qualit

Loans and Leases (Credit Quality Indicator At Amortized Cost By Origination Year) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	$ 2,955.4	$ 7,448.6
2020/2019	6,098.2	3,667.9
2019/2018	3,311.5	1,352.6
2018/2017	1,243.5	1,123.1
2017/2016	1,007.9	1,254.8
PRIOR	3,926.4	3,128.5
REVOLVING LOANS	15,462.4	15,453.6
REVOLVING LOANS CONVERTED TO TERM LOANS	339	330.6
TOTAL LOANS AND LEASES	34,344.3	33,759.7
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	2,103.8	3,772.7
2020/2019	2,637.9	2,187.7
2019/2018	1,936.7	990.3
2018/2017	915.4	725
2017/2016	661.7	749.9
PRIOR	1,863.1	1,285.8
REVOLVING LOANS	5,680.5	5,490.9
REVOLVING LOANS CONVERTED TO TERM LOANS	48.8	59.7
TOTAL LOANS AND LEASES	15,847.9	15,262
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	560.2	1,491.5
2020/2019	1,384.6	1,170.9
2019/2018	935.3	596
2018/2017	555.8	544.2
2017/2016	486.6	553.6
PRIOR	1,099	622.1
REVOLVING LOANS	5,016.8	5,042.2
REVOLVING LOANS CONVERTED TO TERM LOANS	34.8	37.8
TOTAL LOANS AND LEASES	10,073.1	10,058.3
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	334.2	663.8
2020/2019	653.5	546
2019/2018	332.8	204.6
2018/2017	179.2	96
2017/2016	103.4	396
PRIOR	786	448.8
REVOLVING LOANS	3,597	3,742.4
REVOLVING LOANS CONVERTED TO TERM LOANS	1.2	5.5
TOTAL LOANS AND LEASES	5,987.3	6,103.1
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	196.1	793.4
2020/2019	697.7	505.1
2019/2018	524.6	354.1
2018/2017	339.9	405.4
2017/2016	343.7	134.6
PRIOR	288.1	167.3
REVOLVING LOANS	1,351.5	1,238.7
REVOLVING LOANS CONVERTED TO TERM LOANS	33.6	32.3
TOTAL LOANS AND LEASES	3,775.2	3,630.9
Commercial | Commercial and Institutional | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	29.9	34.3
2020/2019	33.4	119.8
2019/2018	77.9	37.3
2018/2017	36.7	42.8
2017/2016	39.5	23
PRIOR	24.9	6
REVOLVING LOANS	68.3	61.1
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	310.6	324.3
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	258.2	1,124.7
2020/2019	1,112.4	976.2
2019/2018	960.6	392.3
2018/2017	357.5	169.7
2017/2016	164	196.3
PRIOR	667.6	494.4
REVOLVING LOANS	181.4	184.7
REVOLVING LOANS CONVERTED TO TERM LOANS	12.2	20.1
TOTAL LOANS AND LEASES	3,713.9	3,558.4
Commercial | Commercial Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	124.7	406.3
2020/2019	341.5	109.2
2019/2018	153.4	27.6
2018/2017	59.8	36.5
2017/2016	24.3	11.8
PRIOR	113.5	99.4
REVOLVING LOANS	82.6	124.3
REVOLVING LOANS CONVERTED TO TERM LOANS	2.8	8.7
TOTAL LOANS AND LEASES	902.6	823.8
Commercial | Commercial Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	121.4	703.1
2020/2019	752.7	811.8
2019/2018	752	332.7
2018/2017	282.2	107.4
2017/2016	115.8	184.5
PRIOR	542.7	382.8
REVOLVING LOANS	98.8	60.4
REVOLVING LOANS CONVERTED TO TERM LOANS	9.4	11.4
TOTAL LOANS AND LEASES	2,675	2,594.1
Commercial | Commercial Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	12.1	15.3
2020/2019	18.2	55.2
2019/2018	55.2	32
2018/2017	15.5	25.8
2017/2016	23.9	0
PRIOR	11.4	12.2
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	136.3	140.5
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	1,007	868.3
2020/2019	140.9	40.6
2019/2018	40.8	2
2018/2017	2.1	11.1
2017/2016	11.1	0
PRIOR	85.2	157.9
REVOLVING LOANS	482.3	264
REVOLVING LOANS CONVERTED TO TERM LOANS	1.8	1.8
TOTAL LOANS AND LEASES	1,771.2	1,345.7
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	724.7	555.2
2020/2019	112.9	16.8
2019/2018	17	0
2018/2017	0	11.1
2017/2016	11.1	0
PRIOR	0	0
REVOLVING LOANS	270	78.5
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	1,135.7	661.6
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	282.1	313.1
2020/2019	28	0.7
2019/2018	0.7	2
2018/2017	2.1	0
2017/2016	0	0
PRIOR	85.2	157.9
REVOLVING LOANS	129.5	39.2
REVOLVING LOANS CONVERTED TO TERM LOANS	1.8	1.8
TOTAL LOANS AND LEASES	529.4	514.7
Commercial | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	0.2	0
2020/2019	0	23.1
2019/2018	23.1	0
2018/2017	0	0
2017/2016	0	0
PRIOR	0	0
REVOLVING LOANS	82.8	146.3
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	106.1	169.4
Commercial | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	0	0
2020/2019	0	0
2019/2018	0	0
2018/2017	0	0
2017/2016	0	0
PRIOR	11.3	11.4
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	11.3	11.4
Commercial | Lease Financing, net | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	0	0
2020/2019	0	0
2019/2018	0	0
2018/2017	0	0
2017/2016	0	0
PRIOR	11.3	11.4
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	11.3	11.4
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	278.4	288.2
2020/2019	0	0
2019/2018	0	0
2018/2017	0	0
2017/2016	0	0
PRIOR	0	0
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	278.4	288.2
Commercial | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	135.8	81.7
2020/2019	0	0
2019/2018	0	0
2018/2017	0	0
2017/2016	0	0
PRIOR	0	0
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	135.8	81.7
Commercial | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	142.6	206.5
2020/2019	0	0
2019/2018	0	0
2018/2017	0	0
2017/2016	0	0
PRIOR	0	0
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	142.6	206.5
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	851.6	3,675.9
2020/2019	3,460.3	1,480.2
2019/2018	1,374.8	362.3
2018/2017	328.1	398.1
2017/2016	346.2	504.9
PRIOR	2,063.3	1,842.7
REVOLVING LOANS	9,781.9	9,962.7
REVOLVING LOANS CONVERTED TO TERM LOANS	290.2	270.9
TOTAL LOANS AND LEASES	18,496.4	18,497.7
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	280.2	1,166.7
2020/2019	1,108.6	754.1
2019/2018	718.7	191.1
2018/2017	180.5	124
2017/2016	118.7	87.7
PRIOR	241.5	213.6
REVOLVING LOANS	9,128.3	9,021.2
REVOLVING LOANS CONVERTED TO TERM LOANS	271	256.7
TOTAL LOANS AND LEASES	12,047.5	11,815.1
Personal | Private Client | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	50.9	668.6
2020/2019	567.3	273.7
2019/2018	122.5	51.7
2018/2017	43.7	60.4
2017/2016	54.5	10.2
PRIOR	141.5	136.1
REVOLVING LOANS	5,283.6	5,392.8
REVOLVING LOANS CONVERTED TO TERM LOANS	59.1	47.9
TOTAL LOANS AND LEASES	6,323.1	6,641.4
Personal | Private Client | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	229.2	492.1
2020/2019	535.5	479.9
2019/2018	595.7	117.3
2018/2017	115.1	60.4
2017/2016	64.2	77.5
PRIOR	100	77.5
REVOLVING LOANS	3,805.1	3,564.7
REVOLVING LOANS CONVERTED TO TERM LOANS	210.6	207.3
TOTAL LOANS AND LEASES	5,655.4	5,076.7
Personal | Private Client | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	0.1	6
2020/2019	5.8	0.5
2019/2018	0.5	22.1
2018/2017	21.7	3.2
2017/2016	0	0
PRIOR	0	0
REVOLVING LOANS	39.6	63.7
REVOLVING LOANS CONVERTED TO TERM LOANS	1.3	1.5
TOTAL LOANS AND LEASES	69	97
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	526.1	2,424.2
2020/2019	2,332.3	685.2
2019/2018	615.6	159.4
2018/2017	136.9	273.6
2017/2016	227.1	416.7
PRIOR	1,811.6	1,619.1
REVOLVING LOANS	411.7	448.4
REVOLVING LOANS CONVERTED TO TERM LOANS	5.6	9.1
TOTAL LOANS AND LEASES	6,066.9	6,035.7
Personal | Residential Real Estate | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	375.1	1,554.3
2020/2019	1,440.3	317.4
2019/2018	247.7	42.9
2018/2017	25.3	109.9
2017/2016	99.1	205.1
PRIOR	771.4	627.8
REVOLVING LOANS	143.7	152.8
REVOLVING LOANS CONVERTED TO TERM LOANS	0	1.7
TOTAL LOANS AND LEASES	3,102.6	3,011.9
Personal | Residential Real Estate | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	150.7	854.6
2020/2019	877.9	359.5
2019/2018	359.8	115.8
2018/2017	111	163.2
2017/2016	127.5	209.7
PRIOR	957.6	896.5
REVOLVING LOANS	245.4	273.1
REVOLVING LOANS CONVERTED TO TERM LOANS	5.6	7.4
TOTAL LOANS AND LEASES	2,835.5	2,879.8
Personal | Residential Real Estate | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	0.3	15.3
2020/2019	14.1	8.3
2019/2018	8.1	0.7
2018/2017	0.6	0.5
2017/2016	0.5	1.9
PRIOR	82.6	94.8
REVOLVING LOANS	22.6	22.5
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	128.8	144
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	0	36
2020/2019	19.4	40.9
2019/2018	40.5	11.8
2018/2017	10.7	0.5
2017/2016	0.4	0.5
PRIOR	10.2	10
REVOLVING LOANS	241.9	493.1
REVOLVING LOANS CONVERTED TO TERM LOANS	13.6	5.1
TOTAL LOANS AND LEASES	336.7	597.9
Personal | Non-U.S. | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	0	23.3
2020/2019	9.2	14.9
2019/2018	32.3	0
2018/2017	0	0
2017/2016	0	0
PRIOR	1.1	1.8
REVOLVING LOANS	65.9	275.6
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	108.5	315.6
Personal | Non-U.S. | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	0	12.7
2020/2019	10.2	26
2019/2018	8.2	11.8
2018/2017	10.7	0.5
2017/2016	0.4	0.5
PRIOR	8.8	7.9
REVOLVING LOANS	176	217.5
REVOLVING LOANS CONVERTED TO TERM LOANS	13.6	5.1
TOTAL LOANS AND LEASES	227.9	282
Personal | Non-U.S. | 6 to 9 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	0	0
2020/2019	0	0
2019/2018	0	0
2018/2017	0	0
2017/2016	0	0
PRIOR	0.3	0.3
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	0.3	0.3
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	45.3	49
2020/2019	0	0
2019/2018	0	0
2018/2017	0	0
2017/2016	0	0
PRIOR	0	0
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	45.3	49
Personal | Other | 1 to 3 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	26.8	34.6
2020/2019	0	0
2019/2018	0	0
2018/2017	0	0
2017/2016	0	0
PRIOR	0	0
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	26.8	34.6
Personal | Other | 4 to 5 Category
Financing Receivable, Credit Quality Indicator [Line Items]
2021/2020	18.5	14.4
2020/2019	0	0
2019/2018	0	0
2018/2017	0	0
2017/2016	0	0
PRIOR	0	0
REVOLVING LOANS	0	0
REVOLVING LOANS CONVERTED TO TERM LOANS	0	0
TOTAL LOANS AND LEASES	$ 18.5	$ 14.4

Loans and Leases (Delinquency S

Loans and Leases (Delinquency Status) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	$ 34,016.1	$ 33,395.6
TOTAL ACCRUAL	34,220.5	33,628
NONACCRUAL	123.8	131.7
TOTAL LOANS AND LEASES	34,344.3	33,759.7
NONACCRUAL WITH NO ALLOWANCE	96.1	98.1
Other Real Estate Owned	1.5	0.7
Total Nonaccrual Assets	125.3	132.4
30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	165.4	209.5
60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	15	14
90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	24	8.9
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	15,745.9	15,038.5
TOTAL ACCRUAL	15,786.5	15,195.4
NONACCRUAL	61.4	66.6
TOTAL LOANS AND LEASES	15,847.9	15,262
NONACCRUAL WITH NO ALLOWANCE	42.1	41.4
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	10,024.5	9,877
TOTAL ACCRUAL	10,051.8	10,031.9
NONACCRUAL	21.3	26.4
TOTAL LOANS AND LEASES	10,073.1	10,058.3
NONACCRUAL WITH NO ALLOWANCE	9.9	9.1
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	3,660.5	3,516.2
TOTAL ACCRUAL	3,673.8	3,518.2
NONACCRUAL	40.1	40.2
TOTAL LOANS AND LEASES	3,713.9	3,558.4
NONACCRUAL WITH NO ALLOWANCE	32.2	32.3
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	1,771.2	1,345.7
TOTAL ACCRUAL	1,771.2	1,345.7
NONACCRUAL	0	0
TOTAL LOANS AND LEASES	1,771.2	1,345.7
NONACCRUAL WITH NO ALLOWANCE	0	0
Commercial | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	11.3	11.4
TOTAL ACCRUAL	11.3	11.4
NONACCRUAL	0	0
TOTAL LOANS AND LEASES	11.3	11.4
NONACCRUAL WITH NO ALLOWANCE	0	0
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	278.4	288.2
TOTAL ACCRUAL	278.4	288.2
NONACCRUAL	0	0
TOTAL LOANS AND LEASES	278.4	288.2
NONACCRUAL WITH NO ALLOWANCE	0	0
Commercial | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	33.8	155.7
Commercial | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	25.1	153.7
Commercial | 30 – 59 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	8.7	2
Commercial | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 30 – 59 DAYS PAST DUE | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 30 – 59 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	2.2	1.2
Commercial | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	2.2	1.2
Commercial | 60 – 89 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 60 – 89 DAYS PAST DUE | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 60 – 89 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	4.6	0
Commercial | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 90 DAYS OR MORE PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	4.6	0
Commercial | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 90 DAYS OR MORE PAST DUE | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Commercial | 90 DAYS OR MORE PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	18,270.2	18,357.1
TOTAL ACCRUAL	18,434	18,432.6
NONACCRUAL	62.4	65.1
TOTAL LOANS AND LEASES	18,496.4	18,497.7
NONACCRUAL WITH NO ALLOWANCE	54	56.7
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	11,912.3	11,765.4
TOTAL ACCRUAL	12,044.6	11,812.2
NONACCRUAL	2.9	2.9
TOTAL LOANS AND LEASES	12,047.5	11,815.1
NONACCRUAL WITH NO ALLOWANCE	2.9	2.9
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	5,976.1	5,946
TOTAL ACCRUAL	6,007.4	5,973.5
NONACCRUAL	59.5	62.2
TOTAL LOANS AND LEASES	6,066.9	6,035.7
NONACCRUAL WITH NO ALLOWANCE	51.1	53.8
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	336.5	596.7
TOTAL ACCRUAL	336.7	597.9
NONACCRUAL	0	0
TOTAL LOANS AND LEASES	336.7	597.9
NONACCRUAL WITH NO ALLOWANCE	0	0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	45.3	49
TOTAL ACCRUAL	45.3	49
NONACCRUAL	0	0
TOTAL LOANS AND LEASES	45.3	49
NONACCRUAL WITH NO ALLOWANCE	0	0
Personal | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	131.6	53.8
Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	103.4	29.1
Personal | 30 – 59 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	28	23.5
Personal | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0.2	1.2
Personal | 30 – 59 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Personal | 60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	12.8	12.8
Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	11.1	9.9
Personal | 60 – 89 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	1.7	2.9
Personal | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Personal | 60 – 89 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Personal | 90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	19.4	8.9
Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	17.8	7.8
Personal | 90 DAYS OR MORE PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	1.6	1.1
Personal | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	0	0
Personal | 90 DAYS OR MORE PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
PAST DUE	$ 0	$ 0

Loans and Leases (Troubled Debt

Loans and Leases (Troubled Debt Restructurings) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)contract	Mar. 31, 2020USD ($)contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	9	8
RECORDED INVESTMENT	$ 41.2	$ 25.3
UNPAID PRINCIPAL BALANCE	$ 43.2	$ 25.7
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	7	2
RECORDED INVESTMENT	$ 41	$ 24.3
UNPAID PRINCIPAL BALANCE	$ 42.9	$ 24.5
Commercial | Commercial and Institutional
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	6	2
RECORDED INVESTMENT	$ 19.6	$ 24.3
UNPAID PRINCIPAL BALANCE	$ 19.6	$ 24.5
Commercial | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	1
RECORDED INVESTMENT	$ 21.4
UNPAID PRINCIPAL BALANCE	$ 23.3
Personal
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	2	6
RECORDED INVESTMENT	$ 0.2	$ 1
UNPAID PRINCIPAL BALANCE	$ 0.3	$ 1.2
Personal | Residential Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	2	6
RECORDED INVESTMENT	$ 0.2	$ 1
UNPAID PRINCIPAL BALANCE	$ 0.3	$ 1.2

Loans and Leases (COVID-19 Loan

Loans and Leases (COVID-19 Loan Modifications Not Considered TDRS) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)contract	Mar. 31, 2020contract
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	9	8
CARES Act | Active Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	25,000,000
RECORDED INVESTMENT	$ 9.5
UNPAID PRINCIPAL BALANCE	0.2
DEFERRED INTEREST AMOUNT	$ 0.2
CARES Act | Completed Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	595,000,000
RECORDED INVESTMENT	$ 1,030.2
UNPAID PRINCIPAL BALANCE	1.4
DEFERRED INTEREST AMOUNT	$ 8.4
Commercial
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	7	2
Commercial | CARES Act | Completed Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	181,000,000
RECORDED INVESTMENT	$ 695.6
UNPAID PRINCIPAL BALANCE	0
DEFERRED INTEREST AMOUNT	$ 5.2
Commercial | Commercial and Institutional
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	6	2
Commercial | Commercial and Institutional | CARES Act | Completed Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	90,000,000
RECORDED INVESTMENT	$ 238.4
UNPAID PRINCIPAL BALANCE	0
DEFERRED INTEREST AMOUNT	$ 2
Commercial | Commercial Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	1
Commercial | Commercial Real Estate | CARES Act | Completed Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	91,000,000
RECORDED INVESTMENT	$ 457.2
UNPAID PRINCIPAL BALANCE	0
DEFERRED INTEREST AMOUNT	$ 3.2
Personal
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	2	6
Personal | CARES Act | Active Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	25,000,000
RECORDED INVESTMENT	$ 9.5
UNPAID PRINCIPAL BALANCE	0.2
DEFERRED INTEREST AMOUNT	$ 0.2
Personal | CARES Act | Completed Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	414,000,000
RECORDED INVESTMENT	$ 334.6
UNPAID PRINCIPAL BALANCE	1.4
DEFERRED INTEREST AMOUNT	$ 3.2
Personal | Private Client | CARES Act | Completed Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	32,000,000
RECORDED INVESTMENT	$ 169.8
UNPAID PRINCIPAL BALANCE	0
DEFERRED INTEREST AMOUNT	$ 1.2
Personal | Residential Real Estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	2	6
Personal | Residential Real Estate | CARES Act | Active Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	25,000,000
RECORDED INVESTMENT	$ 9.5
UNPAID PRINCIPAL BALANCE	0.2
DEFERRED INTEREST AMOUNT	$ 0.2
Personal | Residential Real Estate | CARES Act | Completed Deferral
Financing Receivable, Troubled Debt Restructuring [Line Items]
NUMBER OF LOANS AND LEASES | contract	382,000,000
RECORDED INVESTMENT	$ 164.8
UNPAID PRINCIPAL BALANCE	1.4
DEFERRED INTEREST AMOUNT	$ 2

Allowance for Credit Losses (Ch

Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
LOANS AND LEASES
Balance at Beginning of Period	$ 190,700,000	$ 104,500,000
Charge-Offs	(400,000)	(1,800,000)
Recoveries	1,300,000	1,100,000
Net (Charge-Offs) Recoveries	900,000	(700,000)
Provision for Credit Losses	(26,200,000)	45,600,000
Balance at End of Period	165,400,000	147,200,000
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	61,100,000	19,900,000
Charge-Offs	0	0
Recoveries	0	0
Net (Charge-Offs) Recoveries	0	0
Provision for Credit Losses	(6,000,000)	11,600,000
Balance at End of Period	55,100,000	40,400,000
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	7,300,000	0
Charge-Offs	0	0
Recoveries	0	0
Net (Charge-Offs) Recoveries	0	0
Provision for Credit Losses	1,300,000	2,900,000
Balance at End of Period	8,600,000	9,500,000
OTHER FINANCIAL ASSETS
Balance at Beginning of Period	800,000	0
Charge-Offs	0	0
Recoveries	0	0
Net (Charge-Offs) Recoveries	0	0
Provision for Credit Losses	900,000	700,000
Balance at End of Period	1,700,000	1,100,000
TOTAL
Balance at Beginning of Period	259,900,000	124,400,000
Charge-Offs	(400,000)	(1,800,000)
Recoveries	1,300,000	1,100,000
Net (Charge-Offs) Recoveries	900,000	(700,000)
Provision for Credit Losses	(30,000,000)	60,800,000
Balance at End of Period	230,800,000	198,200,000
Corporate Debt
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	800,000	0
Provision for Credit Losses	300,000	1,900,000
Balance at End of Period	1,100,000	2,700,000
TOTAL
Provision for Credit Losses	$ 0	200,000
Cumulative Effect Adjustment
LOANS AND LEASES
Balance at Beginning of Period		(2,200,000)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		8,900,000
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		6,600,000
Cumulative Effect Adjustment | Commercial and Consumer Portfolio Segment
LOANS AND LEASES
Balance at Beginning of Period		(2,200,000)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		8,900,000
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		6,600,000
OTHER FINANCIAL ASSETS
Balance at Beginning of Period		400,000
TOTAL
Balance at Beginning of Period		13,700,000
Cumulative Effect Adjustment | Corporate Debt
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		800,000
Adjusted Balance
LOANS AND LEASES
Balance at Beginning of Period		102,300,000
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		28,800,000
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		6,600,000
OTHER FINANCIAL ASSETS
Balance at Beginning of Period		400,000
TOTAL
Balance at Beginning of Period		138,100,000
Adjusted Balance | Corporate Debt
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		$ 800,000

Allowance for Credit Losses (Na

Allowance for Credit Losses (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2020
Receivables [Abstract]
Accounting Standards Update [Extensible List]			us-gaap:AccountingStandardsUpdate201613Member
Allowance for credit loss	$ 165.4	$ 147.2	$ 104.5	$ 190.7
Stockholders equity	(11,457.9)	(10,879.7)	(11,091)	(11,688.3)
Credit loss expense (reversal) and available-for-sale, allowance for credit loss	(30)	61
Net (charge-offs) recoveries	$ 0.9	(0.7)
Time period used for projecting future conditions to estimate credit losses	2 years
Other financial assets, allowance for credit loss	$ 1.7	$ 1.1	$ 0	$ 0.8

Allowance for Credit Losses (Ac

Allowance for Credit Losses (Accrued Interest) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Receivables [Abstract]
Loans and Leases	$ 59.4	$ 55.3
Debt Securities
Held to Maturity	19.8	26.5
Available for Sale	136.1	153.6
Other Financial Assets	$ 1.6	$ 1.4

Allowance for Credit Losses (_2

Allowance for Credit Losses (Changes in Allowance for Credit Losses Related to Loan and Leases) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
LOANS AND LEASES
Balance at Beginning of Period	$ 190.7	$ 104.5
Charge-Offs	(0.4)	(1.8)
Recoveries	1.3	1.1
Net (Charge-Offs) Recoveries	0.9	(0.7)
Provision for Credit Losses	(26.2)	45.6
Balance at End of Period	165.4	147.2
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	61.1	19.9
Charge-Offs	0	0
Recoveries	0	0
Net (Charge-Offs) Recoveries	0	0
Provision for Credit Losses	(6)	11.6
Balance at End of Period	55.1	40.4
COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period	142.2	58.1
Charge-Offs	0	(0.1)
Recoveries	0	0.7
Net (Charge-Offs) Recoveries	0	0.6
Provision for Credit Losses	(17.5)	41.9
Balance at End of Period	124.7	94.7
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	57.6	15.8
Charge-Offs	0	0
Recoveries	0	0
Net (Charge-Offs) Recoveries	0	0
Provision for Credit Losses	(5.9)	11.1
Balance at End of Period	51.7	38.8
PERSONAL
LOANS AND LEASES
Balance at Beginning of Period	48.5	46.4
Charge-Offs	(0.4)	(1.7)
Recoveries	1.3	0.4
Net (Charge-Offs) Recoveries	0.9	(1.3)
Provision for Credit Losses	(8.7)	3.7
Balance at End of Period	40.7	52.5
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period	3.5	4.1
Charge-Offs	0	0
Recoveries	0	0
Net (Charge-Offs) Recoveries	0	0
Provision for Credit Losses	(0.1)	0.5
Balance at End of Period	$ 3.4	1.6
Cumulative Effect Adjustment
LOANS AND LEASES
Balance at Beginning of Period		(2.2)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		8.9
Cumulative Effect Adjustment | COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period		(5.9)
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		11.9
Cumulative Effect Adjustment | PERSONAL
LOANS AND LEASES
Balance at Beginning of Period		3.7
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		(3)
Adjusted Balance
LOANS AND LEASES
Balance at Beginning of Period		102.3
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		28.8
Adjusted Balance | COMMERCIAL
LOANS AND LEASES
Balance at Beginning of Period		52.2
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		27.7
Adjusted Balance | PERSONAL
LOANS AND LEASES
Balance at Beginning of Period		50.1
UNDRAWN LOAN COMMITMENTS AND STANDBY LETTERS OF CREDIT
Balance at Beginning of Period		$ 1.1

Allowance for Credit Losses (Re

Allowance for Credit Losses (Recorded Investments in Loans and Leases) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Loans and Leases
Evaluated on an Individual Basis	$ 123.8	$ 131.7
Evaluated on a Collective Basis	34,220.5	33,628
TOTAL LOANS AND LEASES	34,344.3	33,759.7
Allowance for Credit Losses on Credit Exposures
Evaluated on an Individual Basis	10.9	9.1
Evaluated on a Collective Basis	154.5	181.6
Allowance Assigned to Loans and Leases	165.4	190.7	$ 147.2	$ 104.5
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0	1.6
Evaluated on a Collective Basis	55.1	59.5
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	55.1	61.1	40.4	19.9
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	220.5	251.8
COMMERCIAL
Loans and Leases
Evaluated on an Individual Basis	61.4	66.6
Evaluated on a Collective Basis	15,786.5	15,195.4
TOTAL LOANS AND LEASES	15,847.9
Allowance for Credit Losses on Credit Exposures
Evaluated on an Individual Basis	10.6	8.8
Evaluated on a Collective Basis	114.1	133.4
Allowance Assigned to Loans and Leases	124.7	142.2
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0	1.6
Evaluated on a Collective Basis	51.7	56
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	51.7	57.6
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	176.4	199.8
Personal
Loans and Leases
Evaluated on an Individual Basis	62.4	65.1
Evaluated on a Collective Basis	18,434	18,432.6
TOTAL LOANS AND LEASES	18,496.4
Allowance for Credit Losses on Credit Exposures
Evaluated on an Individual Basis	0.3	0.3
Evaluated on a Collective Basis	40.4	48.2
Allowance Assigned to Loans and Leases	40.7	48.5
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Evaluated on an Individual Basis	0	0
Evaluated on a Collective Basis	3.4	3.5
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	3.4	3.5
Total Allowance Assigned to Loans and Leases and Undrawn Loan Commitments and Standby Letters of Credit	44.1	52
COMMERCIAL
Loans and Leases
TOTAL LOANS AND LEASES	15,847.9	15,262
Allowance for Credit Losses on Credit Exposures
Allowance Assigned to Loans and Leases	124.7	142.2	94.7	58.1
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	51.7	57.6	38.8	15.8
Personal
Loans and Leases
TOTAL LOANS AND LEASES	18,496.4	18,497.7
Allowance for Credit Losses on Credit Exposures
Allowance Assigned to Loans and Leases	40.7	48.5	52.5	46.4
Allowance for Undrawn Loan Commitments and Standby Letters of Credit
Allowance Assigned to Undrawn Loan Commitments and Standby Letters of Credit	$ 3.4	$ 3.5	$ 1.6	$ 4.1

Allowance for Credit Losses (_3

Allowance for Credit Losses (Changes in The Allowance for Credit Losses Related to Debt Securities Held to Maturity) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	$ 7.3	$ 0
Provision for Credit Losses	1.3	2.9
Balance at End of Period	8.6	9.5
Cumulative Effect Adjustment
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		6.6
Adjusted Balance
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		6.6
CORPORATE DEBT
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	0.8	0
Provision for Credit Losses	0.3	1.9
Balance at End of Period	1.1	2.7
CORPORATE DEBT | Cumulative Effect Adjustment
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0.8
CORPORATE DEBT | Adjusted Balance
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0.8
Non-U.S. Government
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	0.2	0
Provision for Credit Losses	0.7	0.1
Balance at End of Period	0.9	0.4
Non-U.S. Government | Cumulative Effect Adjustment
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0.3
Non-U.S. Government | Adjusted Balance
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0.3
SUB-SOVEREIGN, SUPERNATIONAL, AND NON-U.S. AGENCY BONDS
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	1.2	0
Provision for Credit Losses	0.6	0.4
Balance at End of Period	1.8	1.3
SUB-SOVEREIGN, SUPERNATIONAL, AND NON-U.S. AGENCY BONDS | Cumulative Effect Adjustment
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0.9
SUB-SOVEREIGN, SUPERNATIONAL, AND NON-U.S. AGENCY BONDS | Adjusted Balance
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0.9
CERTIFICATE OF DEPOSITS
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	0	0
Provision for Credit Losses	0	0.2
Balance at End of Period	0	0.2
CERTIFICATE OF DEPOSITS | Cumulative Effect Adjustment
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0
CERTIFICATE OF DEPOSITS | Adjusted Balance
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0
COVERED BONDS
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	0.1	0
Provision for Credit Losses	0	0.1
Balance at End of Period	0.1	0.1
COVERED BONDS | Cumulative Effect Adjustment
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0
COVERED BONDS | Adjusted Balance
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		0
OTHER
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period	5	0
Provision for Credit Losses	(0.3)	0.2
Balance at End of Period	$ 4.7	4.8
OTHER | Cumulative Effect Adjustment
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		4.6
OTHER | Adjusted Balance
DEBT SECURITIES HELD TO MATURITY
Balance at Beginning of Period		$ 4.6

Pledged and Restricted Assets_2

Pledged and Restricted Assets (Type of Pledged Assets) (Details) - USD ($) $ in Billions	Mar. 31, 2021	Dec. 31, 2020
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 45.9	$ 47.5
Obligations of States and Political Subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	3	2.9
Government Sponsored Agency and Other Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	30.6	32.5
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Total Pledged Assets	$ 12.3	$ 12.1

Pledged and Restricted Assets_3

Pledged and Restricted Assets (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2021	Dec. 31, 2020
Financial Instruments Owned and Pledged as Collateral [Line Items]
Security owned and pledged as collateral, fair value		$ 45,900,000,000	$ 47,500,000,000
Securities eligible to be repledged or sold		93,400,000	33,500,000
Collateral securities repledged, delivered, or used		0	0
Average deposits maintained to meet Federal Reserve Bank reserve requirements	$ 1,700,000,000
Collateral Requirements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Security owned and pledged as collateral, fair value		$ 1,600,000,000	$ 5,700,000,000

Pledged and Restricted Assets_4

Pledged and Restricted Assets (Fair Value Of Available For Sale Debt Securities Included In Pledged Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Financial Instruments Owned and Pledged as Collateral [Line Items]
Debt Securities Available for Sale	$ 45,900	$ 47,500
SECURITIES SOLD UNDER AGREEMENTS TO REPURCHASE
Financial Instruments Owned and Pledged as Collateral [Line Items]
Debt Securities Available for Sale	93	33
DERIVATIVE CONTRACTS
Financial Instruments Owned and Pledged as Collateral [Line Items]
Debt Securities Available for Sale	$ 29.3	$ 27.1

Pledged and Restricted Assets_5

Pledged and Restricted Assets (Accepted Collateral) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Reverse repurchase agreements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 309.3	$ 1,179.8
Collateral that may not be repledged or sold	800	500
Derivative contracts
Financial Instruments Owned and Pledged as Collateral [Line Items]
Collateral that may be repledged or sold	$ 8.4	$ 0.9

Goodwill and Other Intangible_2

Goodwill and Other Intangibles (Goodwill by Reporting Segment) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 707.2
Foreign Exchange Rates	(3.2)
Goodwill, Ending Balance	704
CORPORATE & INSTITUTIONAL SERVICES
Goodwill [Roll Forward]
Goodwill, Beginning Balance	636
Foreign Exchange Rates	(3.2)
Goodwill, Ending Balance	632.8
WEALTH MANAGEMENT
Goodwill [Roll Forward]
Goodwill, Beginning Balance	71.2
Foreign Exchange Rates	0
Goodwill, Ending Balance	$ 71.2

Goodwill and Other Intangible_3

Goodwill and Other Intangibles - Other Intangible Assets and Capitalized Software (Detail) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 210	$ 221.3
Less: Accumulated Amortization	106.2	108.7
Net Book Value	103.8	112.6
Computer Software
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,404.8	4,337.4
Less: Accumulated Amortization	2,810.5	2,744.5
Net Book Value	$ 1,594.3	$ 1,592.9

Goodwill and Other Intangible_4

Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Acquired Finite-Lived Intangible Assets [Line Items]
Other Intangibles Amortization	$ 4.3	$ 4.1
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Other Intangibles Amortization	4.3	4.1
Estimated future amortization expense for 2021	10.5
Estimated future amortization expense for 2022	10.1
Estimated future amortization expense for 2023	9.8
Estimated future amortization expense for 2024	9.7
Estimated future amortization expense for 2025	9.1
Computer Software
Acquired Finite-Lived Intangible Assets [Line Items]
Other Intangibles Amortization	$ 94	$ 91.6

Reporting Segments (Results of

Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021USD ($)segment	Mar. 31, 2020USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | segment	2
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 1,063.7	$ 1,003.6
Foreign Exchange Trading Income	78.7	88.9
Other Noninterest Income	100.9	87.1
Total Noninterest Income	1,243.3	1,179.6
Net Interest Income	346.7	416.2
Revenue	1,590	1,595.8
Provision for Credit Losses	(30)	61
Noninterest Expense	1,117.5	1,065.6
Income before Income Taxes	502.5	469.2
Provision for Income Taxes	127.4	108.6
Net Income	$ 375.1	$ 360.6
Percentage of Consolidated Net Income	100.00%	100.00%
Average Assets	$ 153,255.8	$ 124,170.5
FTE adjustments	6.6	8.1
CORPORATE & INSTITUTIONAL SERVICES
Noninterest Income
Trust, Investment and Other Servicing Fees	620.5	574.4
Foreign Exchange Trading Income	74.5	85.1
Other Noninterest Income	60.3	41.8
Total Noninterest Income	755.3	701.3
Net Interest Income	160.7	211.3
Revenue	916	912.6
Provision for Credit Losses	(5.4)	25.7
Noninterest Expense	713.1	659.3
Income before Income Taxes	208.3	227.6
Provision for Income Taxes	50.1	49.9
Net Income	$ 158.2	$ 177.7
Percentage of Consolidated Net Income	42.00%	49.00%
Average Assets	$ 120,157.7	$ 92,715.3
WEALTH MANAGEMENT
Noninterest Income
Trust, Investment and Other Servicing Fees	443.2	429.2
Foreign Exchange Trading Income	4.2	3.8
Other Noninterest Income	44.2	42.4
Total Noninterest Income	491.6	475.4
Net Interest Income	186	204.9
Revenue	677.6	680.3
Provision for Credit Losses	(24.6)	35.3
Noninterest Expense	403.1	394.4
Income before Income Taxes	299.1	250.6
Provision for Income Taxes	78.5	60.9
Net Income	$ 220.6	$ 189.7
Percentage of Consolidated Net Income	59.00%	53.00%
Average Assets	$ 33,098.1	$ 31,455.2
OTHER
Noninterest Income
Trust, Investment and Other Servicing Fees	0	0
Foreign Exchange Trading Income	0	0
Other Noninterest Income	(3.6)	2.9
Total Noninterest Income	(3.6)	2.9
Net Interest Income	0	0
Revenue	(3.6)	2.9
Provision for Credit Losses	0	0
Noninterest Expense	1.3	11.9
Income before Income Taxes	(4.9)	(9)
Provision for Income Taxes	(1.2)	(2.2)
Net Income	$ (3.7)	$ (6.8)
Percentage of Consolidated Net Income	(1.00%)	(2.00%)
Average Assets	$ 0	$ 0

Stockholders' Equity (Narrative

Stockholders' Equity (Narrative) (Details) - USD ($)	Jan. 20, 2021	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Jul. 31, 2018
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		10,000,000		10,000,000
Stockholders' equity		$ 11,457,900,000	$ 10,879,700,000	$ 11,688,300,000	$ 11,091,000,000
Common stock dividends (in usd per share)		$ 0.70	$ 0.70
Stock repurchase program, number of shares authorized to be repurchased (in shares)						25,000,000
Stock repurchase, shares (in shares)		1,399,673
Stock repurchase, share-based compensation plan (in shares)		365,697
Stock repurchase, aggregate cost		$ 135,600,000	$ 296,800,000
Average price paid per share for common stock repurchased (in usd per share)		$ 96.91
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		5,000		5,000
Stockholders' equity		$ 493,500,000		$ 493,500,000
Preferred stock, without par value (in dollars per share)		$ 0
Preferred stock, liquidation preference		$ 100,000
Depository shares, liquidation preference per share (in dollars per share)		$ 1,000
Preferred stock, annual dividend rate		4.60%
Preferred stock, dividend payment rate, variable rate		3.202%
Common stock dividends (in usd per share)	$ 2,300
Series E Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		16,000		16,000
Percentage of ownership interest per each depository shares		0.10%
Stockholders' equity		$ 391,400,000		$ 391,400,000
Preferred stock, without par value (in dollars per share)		$ 0
Preferred stock, liquidation preference		$ 25,000
Depository shares, liquidation preference per share (in dollars per share)		$ 25
Preferred stock, annual dividend rate		4.70%
Common stock dividends (in usd per share)	$ 293.75
Series D Preferred Stock, Depositary Shares
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		500,000
Preferred stock, shares issued (in shares)		500,000
Percentage of ownership interest per each depository shares		1.00%
Series E Preferred Stock Depositary Shares
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		16,000,000
Preferred stock, shares issued (in shares)		16,000,000

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) (Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 11,688.3	$ 11,091
Net Change	(362.1)	239.7
Ending balance	11,457.9	10,879.7
TOTAL
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	428	(194.7)
Net Change	(362.1)	239.7
Ending balance	65.9	45
NET UNREALIZED GAINS (LOSSES) ON DEBT SECURITIES AVAILABLE FOR SALE
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	641.8	114
Net Change	(369.7)	199.7
Ending balance	272.1	313.7
NET UNREALIZED (LOSSES) GAINS ON CASH FLOW HEDGES
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(3.2)	(3.7)
Net Change	(5.2)	7.3
Ending balance	(8.4)	3.6
NET FOREIGN CURRENCY ADJUSTMENT
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	144.7	117.8
Net Change	5	25.7
Ending balance	149.7	143.5
NET PENSION AND OTHER POSTRETIREMENT BENEFIT ADJUSTMENTS
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(355.3)	(422.8)
Net Change	7.8	7
Ending balance	$ (347.5)	$ (415.8)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) (Details of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
BEFORE TAX
Net Change	$ (468)	$ 338.3
TAX EFFECT
Net Change	105.9	(98.6)
AFTER TAX
Net Change	(362.1)	239.7
Unrealized Gains (Losses) on Debt Securities Available for Sale
BEFORE TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	(496.5)	266.8
Reclassification Adjustment for (Gains) Losses Included in Net Income	0	0
Net Change	(496.5)	266.8
TAX EFFECT
Unrealized Gains (Losses) on Debt Securities Available for Sale	126.8	(67.1)
Reclassification Adjustment for (Gains) Losses Included in Net Income	0	0
Net Change	126.8	(67.1)
AFTER TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	(369.7)	199.7
Reclassification Adjustment for (Gains) Losses Included in Net Income	0	0
Net Change	(369.7)	199.7
Unrealized Gains (Losses) on Cash Flow Hedges
BEFORE TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(4.5)	(4)
Net Change	(7)	9.7
TAX EFFECT
Reclassification Adjustment for (Gains) Losses Included in Net Income	1.1	1
Net Change	1.8	(2.4)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(3.4)	(3)
Net Change	(5.2)	7.3
Foreign Currency Adjustments
BEFORE TAX
Net Change	25.2	52.3
TAX EFFECT
Net Change	(20.2)	(26.6)
AFTER TAX
Net Change	5	25.7
Foreign Currency Translation Adjustments
BEFORE TAX
Net Change	(57.3)	(89.8)
TAX EFFECT
Net Change	0.5	9.6
AFTER TAX
Net Change	(56.8)	(80.2)
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
BEFORE TAX
Net Change	(0.2)	(0.6)
TAX EFFECT
Net Change	0.1	0.1
AFTER TAX
Net Change	(0.1)	(0.5)
Net Investment Hedge Gains (Losses)
BEFORE TAX
Net Change	82.7	142.7
TAX EFFECT
Net Change	(20.8)	(36.3)
AFTER TAX
Net Change	61.9	106.4
Pension and Other Postretirement Benefit Adjustments
BEFORE TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	(1.3)	(1.3)
Net Change	10.3	9.5
TAX EFFECT
Unrealized Gains (Losses) on Debt Securities Available for Sale	0.3	0.1
Net Change	(2.5)	(2.5)
AFTER TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	(1)	(1.2)
Net Change	7.8	7
Amortization of Net Actuarial Loss
BEFORE TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	11.9	10.9
TAX EFFECT
Reclassification Adjustment for (Gains) Losses Included in Net Income	(2.9)	(2.6)
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	9	8.3
Amortization of Prior Service Cost
BEFORE TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.3)	(0.1)
TAX EFFECT
Reclassification Adjustment for (Gains) Losses Included in Net Income	0.1	0
AFTER TAX
Reclassification Adjustment for (Gains) Losses Included in Net Income	(0.2)	(0.1)
Foreign Exchange Contracts | Unrealized Gains (Losses) on Cash Flow Hedges
BEFORE TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	(2.5)	13.3
TAX EFFECT
Unrealized Gains (Losses) on Debt Securities Available for Sale	0.7	(3.3)
AFTER TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	(1.8)	10
Interest Rate Contracts | Unrealized Gains (Losses) on Cash Flow Hedges
BEFORE TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	0	0.4
TAX EFFECT
Unrealized Gains (Losses) on Debt Securities Available for Sale	0	(0.1)
AFTER TAX
Unrealized Gains (Losses) on Debt Securities Available for Sale	$ 0	$ 0.3

Net Income Per Common Share (Ne

Net Income Per Common Share (Net Income Per Common Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Basic Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	208,112,824	208,881,131
Net Income	$ 375.1	$ 360.6
Less: Dividends on Preferred Stock	16.2	30.5
Net Income Applicable to Common Stock	358.9	330.1
Less: Earnings Allocated to Participating Securities	3.7	3.9
Earnings Allocated to Common Shares Outstanding	$ 355.2	$ 326.2
Basic Net Income Per Common Share (in dollars per share)	$ 1.71	$ 1.56
Diluted Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	208,112,824	208,881,131
Plus: Dilutive Effect of Share-based Compensation (in shares)	833,624	935,691
Diluted (in shares)	208,946,448	209,816,822
Earnings Allocated to Common and Potential Common Shares	$ 355.2	$ 326.2
Diluted Net Income Per Common Share (in dollars per share)	$ 1.70	$ 1.55
Common stock equivalents not included in the computation of diluted earnings per share because their inclusion would have been antidilutive (in shares)	0	0

Revenue from Contracts with C_3

Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,063.7	$ 1,003.6
Foreign Exchange Trading Income	78.7	88.9
Treasury Management Fees	11.2	11
Security Commissions and Trading Income	34.8	41.7
Other Operating Income	54.9	34.4
Total Other Noninterest Income	179.6	176
Total Noninterest Income	1,243.3	1,179.6
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	469.7	417.6
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	516.4	510.5
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	18.3	23.5
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 59.3	$ 52

Revenue from Contracts with C_4

Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 1,063.7	$ 1,003.6
Security commissions and trading income	34.8	41.7
Other operating income	54.9	34.4
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Revenue from contract with client	28.7	29
Other Operating Income
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 12.8	$ 10.8

Revenue from Contracts with C_5

Revenue from Contracts with Clients (Contract Receivables) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Total Client Receivables	$ 1,006.4	$ 935.8
Trust Fees Receivable, net
Disaggregation of Revenue [Line Items]
Total Client Receivables	890.2	819.3
Contract with customer, asset, allowance for credit loss	6.7	7.2
Other
Disaggregation of Revenue [Line Items]
Total Client Receivables	$ 116.2	$ 116.5

Net Interest Income (Net Intere

Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Interest Income
Loans and Leases	$ 172	$ 250.2
Securities — Taxable	173.9	241.1
Securities - Non-Taxable	0.4	0.5
Interest-Bearing Due from and Deposits with Banks	2.4	12.8
Federal Reserve and Other Central Bank Deposits and Other	1.2	24.6
Total Interest Income	349.9	529.2
Interest Expense
Deposits	(13.4)	60.9
Federal Funds Purchased	0.1	2
Securities Sold Under Agreements to Repurchase	0	1
Other Borrowings	3.5	29.2
Senior Notes	13.7	17.9
Long-Term Debt	5.3	8.4
Floating Rate Capital Debt	0.6	1.7
Total Interest Expense	9.8	121.1
Net Interest Income	$ 340.1	$ 408.1

Other Operating Income - (Detai

Other Operating Income - (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Components of Other Operating Income [Line Items]
Total Other Operating Income	$ 54.9	$ 34.4
Loan Service Fees
Components of Other Operating Income [Line Items]
Total Other Operating Income	15.4	11.9
Banking Service Fees
Components of Other Operating Income [Line Items]
Total Other Operating Income	12.7	11.4
Other Income
Components of Other Operating Income [Line Items]
Total Other Operating Income	$ 26.8	$ 11.1

Other Operating Expense (Detail

Other Operating Expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Other Income and Expenses [Abstract]
Business Promotion	$ 7.9	$ 18.8
Staff Related	6.8	(3.5)
FDIC Insurance Premiums	3.6	2.5
Other Intangibles Amortization	4.3	4.1
Other Expenses	49.1	39.9
Total Other Operating Expense	$ 71.7	$ 61.8

Pension and Postretirement He_3

Pension and Postretirement Health Care (Net Periodic Pension Expense (Benefit)) (Details) - USD ($)	1 Months Ended	3 Months Ended
	Aug. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Pension Plan
Amortization
Contribution to pension plan		$ 0	$ 0
Supplemental Plan
Defined Benefit plan Net periodic benefit cost
Service Cost		1,300,000	1,100,000
Interest Cost		900,000	1,200,000
Amortization
Actuarial Loss (Gain)		2,100,000	1,800,000
Prior Service Cost		0	0
Net Periodic Pension Expense		4,300,000	4,100,000
Postretirement Health Care Plan
Defined Benefit plan Net periodic benefit cost
Service Cost		0	0
Interest Cost		100,000	200,000
Amortization
Actuarial Loss (Gain)		(100,000)	(200,000)
Prior Service Cost		(200,000)	0
Net Periodic Pension Expense		(200,000)	0
Amortization period for prior service costs	13 years 10 months 24 days
U.S Plans | Pension Plan
Defined Benefit plan Net periodic benefit cost
Service Cost		13,200,000	11,800,000
Interest Cost		9,800,000	10,800,000
Expected Return on Plan Assets		(20,100,000)	(19,200,000)
Amortization
Actuarial Loss (Gain)		9,400,000	8,800,000
Prior Service Cost		(100,000)	(100,000)
Net Periodic Pension Expense		12,200,000	12,100,000
Non U.S. Plans | Pension Plan
Defined Benefit plan Net periodic benefit cost
Service Cost		500,000	500,000
Interest Cost		600,000	700,000
Expected Return on Plan Assets		(600,000)	(700,000)
Settlement Expense		200,000	200,000
Amortization
Actuarial Loss (Gain)		300,000	300,000
Prior Service Cost		0	0
Net Periodic Pension Expense		$ 1,000,000	$ 1,000,000

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
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 50.5	$ 53.8
Tax Benefits Recognized	$ 12.7	$ 13.4
Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, grants in period, gross (in shares)	729,013	763,554
Share-based compensation arrangement by share-based payment award, equity instruments other than options, granted in period, fair value	$ 70.4	$ 76.2
Share-based compensation expense	38.4	40.7
Employee benefits and share-based compensation	4.2	4.3
Restricted Stock Unit Awards | Retirement Eligible Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 21.8	$ 23.2
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, grants in period, gross (in shares)	0	0
Share-based compensation expense	$ 0	$ 0.2
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, options, grants in period, gross (in shares)	200,066	205,847
Share-based compensation arrangement by share-based payment award, equity instruments other than options, granted in period, fair value	$ 19.5	$ 20.8
Share-based compensation expense	12.1	12.9
Performance Stock Units | Retirement Eligible Employees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 9.9	$ 10.8

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Variable Interest Entity [Line Items]
Assets	$ 163,924,100,000		$ 170,003,900,000
Liabilities	152,466,200,000		158,315,600,000
Exposure to loss from liquidity arrangements and obligations to purchase assets	0
Affordable housing tax credits and other tax benefits	23,000,000	$ 16,300,000
Investment company, voluntary fee waived	50,200,000	$ 0
Contractual obligation to provide financial support	0
Other Assets
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, assets	908,100,000		919,600,000
Other Assets | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Assets	863,600,000		874,000,000
Other Liabilities
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, liabilities	313,700,000		351,600,000
Other Liabilities | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Liabilities	$ 298,300,000		$ 335,900,000

Commitments and Contingent Li_2

Commitments and Contingent Liabilities - Summary of Off-Balance Sheet Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Loss Contingencies [Line Items]
ONE YEAR AND LESS	$ 189,438.7	$ 170,021.2
OVER ONE YEAR	18,337	18,441.5
TOTAL	207,775.7	188,462.7
Undrawn Commitments to Extend Credit
Loss Contingencies [Line Items]
Commitments, participated to others	404.2	384.7
Custody Securities Lent with Indemnification
Loss Contingencies [Line Items]
ONE YEAR AND LESS	176,378	157,478
OVER ONE YEAR	0	0
TOTAL	176,378	157,478
Secured by Cash Deposits or Participated to Others | Standby Letters of Credit
Loss Contingencies [Line Items]
TOTAL	23.8	24.2
Undrawn Commitments to Extend Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	11,519.7	11,260.5
OVER ONE YEAR	18,016	17,678
TOTAL	29,535.7	28,938.5
Standby Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	1,474.8	1,228.1
OVER ONE YEAR	321	763.5
TOTAL	1,795.8	1,991.6
Commercial Letters of Credit
Loss Contingencies [Line Items]
ONE YEAR AND LESS	66.2	54.6
OVER ONE YEAR	0	0
TOTAL	$ 66.2	$ 54.6

Commitments and Contingent Li_3

Commitments and Contingent Liabilities (Narrative) (Details) shares in Millions	Sep. 27, 2019USD ($)	Jun. 28, 2018USD ($)	Jun. 30, 2016USD ($)shares	Jun. 30, 2015USD ($)shares	Dec. 31, 2015trust	Mar. 31, 2021USD ($)shares	Dec. 31, 2020USD ($)shares
Loss Contingencies [Line Items]
Minimum securities lending related collateral percentage						100.00%
Commitments and letters of credit						$ 207,775,700,000	$ 188,462,700,000
Loss contingency accrual						$ 0
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
Visa Inc. | Visa Class B Litigation Case
Loss Contingencies [Line Items]
Escrow deposit	$ 300,000,000	$ 600,000,000
Indemnification Agreement
Loss Contingencies [Line Items]
Credit loss liability						$ 0	$ 0

Derivative Financial Instrume_3

Derivative Financial Instruments (Notional and Fair Values of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
NOTIONAL VALUE	$ 335,746.7	$ 346,752.1
Assets	2,509.4	4,097.2
Total Gross Derivatives, asset	3,206.6	4,558.2
Less: Netting	1,977.1	3,507.8
Derivative Assets	1,229.5	1,050.4
Liabilities	2,251.7	3,738
Derivative Liabilities	2,701.3	4,882.8
Less: Netting	2,090.3	2,817.1
Derivative Liabilities	611	2,065.7
Derivatives Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	14,460.7	14,802.3
Assets	380.2	23.8
Liabilities	42.9	321.9
Fair Value Hedges | Derivatives Designated as Hedging under GAAP | Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	4,513.7	4,717.6
Assets	10	8.2
Liabilities	13.7	10.2
Fair Value Hedges | Derivatives Not Designated as Hedging under GAAP
Derivative [Line Items]
NOTIONAL VALUE	321,286	331,949.8
Assets	2,826.4	4,534.4
Liabilities	2,658.4	4,560.9
Fair Value Hedges | Non-Designated Risk Management Derivatives
Derivative [Line Items]
NOTIONAL VALUE	852.5	813.1
Assets	0.7	0.1
Liabilities	34.7	35.4
Fair Value Hedges | Non-Designated Risk Management Derivatives | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	131	67.7
Assets	0.7	0.1
Liabilities	0.1	0.1
Fair Value Hedges | Non-Designated Risk Management Derivatives | Other Financial Derivatives
Derivative [Line Items]
NOTIONAL VALUE	721.5	745.4
Assets	0	0
Liabilities	34.6	35.3
Fair Value Hedges | Client-Related and Trading Derivatives
Derivative [Line Items]
NOTIONAL VALUE	320,433.5	331,136.7
Assets	2,825.7	4,534.3
Liabilities	2,623.7	4,525.5
Fair Value Hedges | Client-Related and Trading Derivatives | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	309,731.3	320,563.4
Assets	2,630.1	4,245.1
Liabilities	2,513.7	4,410.7
Fair Value Hedges | Client-Related and Trading Derivatives | Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	10,702.2	10,573.3
Assets	195.6	289.2
Liabilities	110	114.8
Cash Flow Hedges | Derivatives Designated as Hedging under GAAP | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	6,464.9	6,554.4
Assets	296.7	15.4
Liabilities	20.4	104
Cash Flow Hedges | Derivatives Designated as Hedging under GAAP | Interest Rate Contracts
Derivative [Line Items]
NOTIONAL VALUE	0	50
Assets	0	0.1
Liabilities	0	0
Net Investment Hedges | Derivatives Designated as Hedging under GAAP | Foreign Exchange Contracts
Derivative [Line Items]
NOTIONAL VALUE	3,482.1	3,480.3
Assets	73.5	0.1
Liabilities	$ 8.8	$ 207.7

Derivative Financial Instrume_4

Derivative Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative [Line Items]
Gains or losses reclassified into earnings	$ 0	$ 0
Maximum length of time over which exposure was being hedged	23 months
Net investment gains (losses) recognized in AOCI	$ 82,700,000	$ 142,700,000
Foreign Currency Denominate
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges	(8,000,000)
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	$ 287,900,000

Derivative Financial Instrume_5

Derivative Financial Instruments (Location and Amount of Fair Value And Cash Flow Hedge Derivative Gains And Losses Recorded In Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 349.9	$ 529.2
Interest Expense	9.8	121.1
Other Operating Income	54.9	34.4
INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	(1.6)	(0.5)
Gains (Losses) on cash flow hedges recognized on	5.5	4.1
INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	7	(2.9)
Gains (Losses) on cash flow hedges recognized on	0	0
OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Total gains (losses) recognized on fair value hedges	0	0
Gains (Losses) on cash flow hedges recognized on	(1)	(0.1)
Interest Rate Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	18.4	(76)
Recognized on hedged items	(18.4)	76
Amounts related to interest settlements on derivatives	(1.6)	(0.5)
Interest Rate Contracts | INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(142.9)	150.4
Recognized on hedged items	142.9	(150.4)
Amounts related to interest settlements on derivatives	7	(2.9)
Interest Rate Contracts | OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	0	0
Recognized on hedged items	0	0
Amounts related to interest settlements on derivatives	0	0
Foreign Exchange Contracts | INTEREST INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on cash flow hedges recognized on	5.5	4.1
Foreign Exchange Contracts | INTEREST EXPENSE
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on cash flow hedges recognized on	0	0
Foreign Exchange Contracts | OTHER OPERATING INCOME
Derivative Instruments, Gain (Loss) [Line Items]
Gains (Losses) on cash flow hedges recognized on	$ (1)	$ (0.1)

Derivative Financial Instrume_6

Derivative Financial Instruments (Hedged Items In Fair Value Hedges) (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Carrying value of the hedged items, available for sale debt securities	$ 1,807,400,000	$ 2,075,100,000
Cumulative hedge accounting basis adjustment, available for sale debt securities	35,300,000	48,800,000
Carrying value of the hedged items, senior notes and long-term subordinated debt	2,745,200,000	2,745,100,000
Cumulative hedge accounting basis adjustment, senior notes and long-term subordinated debt	66,500,000	221,500,000
Carrying Value of the Hedged Items	4,552,600,000	4,820,200,000
Cumulative Hedge Accounting Basis Adjustment	101,800,000	270,300,000
Hedged asset fair value hedge discontinued cumulative increase decrease	10,200,000	10,400,000
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
	Mar. 31, 2021	Mar. 31, 2020
Derivatives Not Designated as Hedging under GAAP
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 78.2	$ 102.9
Non-Designated Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	(3.5)	3
Non-Designated Risk Management Derivatives | Foreign Exchange Contracts | Others Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	0.1	0.1
Non-Designated Risk Management Derivatives | Other Financial Derivatives | Others Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	(3.6)	2.9
Client-Related and Trading Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	81.7	99.9
Client-Related and Trading Derivatives | Foreign Exchange Contracts | Foreign Exchange Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	78.7	88.9
Client-Related and Trading Derivatives | Interest Rate Contracts | Security Commissions and Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
AMOUNT OF DERIVATIVE GAINS (LOSSES) RECOGNIZED IN INCOME	$ 3	$ 11

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	Mar. 31, 2021	Dec. 31, 2020
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	$ 2,509.4	$ 4,097.2
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,977.1	3,507.8
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	532.3	589.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	8.4	0.9
NET AMOUNT	523.9	588.5
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	697.2	461
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNT	697.2	461
Total Derivatives
GROSS RECOGNIZED ASSETS	3,206.6	4,558.2
Derivative Assets	1,229.5	1,050.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	8.4	0.9
NET AMOUNT	1,221.1	1,049.5
Securities Purchased under Agreements to Resell
GROSS RECOGNIZED ASSETS	1,109.3	1,596.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	1,109.3	1,596.5
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	1,109.3	1,596.5
Other assets excluding derivatives and non financial instruments	7,600	7,300
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	2,303.8	3,799.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	1,973.5	3,505.3
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	330.3	294.4
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	8.4	0.9
NET AMOUNT	321.9	293.5
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	204	295.9
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	3.6	2.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	200.4	293.4
NET AMOUNT	200.4	293.4
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED ASSETS	1.6	1.6
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	0	0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	1.6	1.6
NET AMOUNT	$ 1.6	$ 1.6

Offsetting of Assets and Liab_4

Offsetting of Assets and Liabilities (Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	$ 2,251.7	$ 3,738
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,090.3	2,817.1
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	161.4	920.9
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.9	0.5
Net Amount	160.5	920.4
Total Derivatives Not Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	449.6	1,144.8
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0
NET AMOUNT	449.6	1,144.8
Offsetting Derivative Liabilities [Abstract]
GROSS RECOGNIZED LIABILITIES	2,701.3	4,882.8
Derivative Liabilities	611	2,065.7
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.9	0.5
NET AMOUNT	610.1	2,065.2
Securities Sold under Agreements to Repurchase
GROSS RECOGNIZED LIABILITIES	95.6	39.8
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	95.6	39.8
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	95.6	39.8
Other liabilities	4,400	3,500
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	2,093.4	3,577.7
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	2,023.7	2,718.6
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	69.7	859.1
GROSS AMOUNTS NOT OFFSET IN THE BALANCE SHEET	0.9	0.5
Net Amount	68.8	858.6
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	123.7	125
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	66.6	98.5
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	57.1	26.5
Net Amount	57.1	26.5
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES		0
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET		0
NET AMOUNTS PRESENTED IN THE BALANCE SHEET		0
Net Amount		0
Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
NET AMOUNTS PRESENTED IN THE BALANCE SHEET	34.6	35.3
Net Amount	34.6	35.3
Other Financial Derivatives | Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
GROSS RECOGNIZED LIABILITIES	34.6	35.3
GROSS AMOUNTS OFFSET IN THE BALANCE SHEET	$ 0	$ 0

Offsetting of Assets and Liab_5

Offsetting of Assets and Liabilities (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Offsetting Assets and Liabilities [Line Items]
Collateral received	$ 8.4	$ 0.9
Gross amounts not offset in the balance sheet	0.9	0.5
Aggregate fair value of all derivative instruments with credit-risk-related contingent features that are in a liability position	401.6	1,648.2
Collateral deposited with derivative counterparties for derivatives instruments with credit-risk-related contingent features that are in a liability position	391.1	1,044
Net maximum amount of termination payments that could have been required	10.5	604.2
Net Investment Hedges
Offsetting Assets and Liabilities [Line Items]
Collateral received	189
Gross amounts not offset in the balance sheet	$ 206.1
Cash collateral received from derivative counterparties and not offset against derivative assets		111
Cash collateral deposited with derivative counterparties not offset against derivative liabilities		$ 49