Basis of Presentation (Policies)	3 Months Ended
Mar. 31, 2026
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	The interim consolidated financial statements of Wintrust Financial Corporation and its subsidiaries (collectively, “Wintrust” or the “Company”) presented herein are unaudited, but in the opinion of management, reflect all necessary adjustments of a normal or recurring nature for a fair presentation of results as of the dates and for the periods covered by the interim consolidated financial statements. The accompanying interim consolidated financial statements are unaudited and do not include information or footnotes necessary for a complete presentation of financial condition, results of operations or cash flows in accordance with U.S. generally accepted accounting principles (“GAAP”). The interim unaudited consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025 (“2025 Form 10-K”). Operating results reported for the period are not necessarily indicative of the results which may be expected for the entire year. Reclassifications of certain prior period amounts have been made to conform to the current period presentation. The preparation of the financial statements requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities. Management believes that the estimates made are reasonable; however, changes in estimates may be required if economic or other conditions develop differently from management’s expectations. Certain policies and accounting principles inherently have a greater reliance on the use of estimates, assumptions and judgments and as such have a greater possibility of producing results that could be materially different than originally reported. Management views critical accounting policies to be those which are highly dependent on subjective or complex judgments, estimates and assumptions, and where changes in those estimates and assumptions could have a significant impact on the financial statements. Management currently views the determination of the allowance for credit losses, including the allowance for loan losses, the allowance for unfunded commitment losses and the allowance for held-to-maturity securities losses, estimations of fair value, the valuations required for impairment testing of goodwill, the valuation and accounting for derivative instruments and income taxes as the accounting areas that require the most subjective and complex judgments, and as such could be the most subject to revision as new information becomes available. Descriptions of the Company’s significant accounting policies are included in Note (1) “Summary of Significant Accounting Policies” of the 2025 Form 10-K. In preparation of these financial statements, subsequent events were evaluated through the time the financial statements were issued. Financial statements are considered issued when they are widely distributed to all shareholders and other financial statement users or filed with the SEC.
Recent Accounting Developments	Disaggregation of Income Statement Expenses In November 2024, the FASB issued Accounting Standards Update (“ASU”) No. 2024-03, “Income Statement – Reporting Comprehensive Income – Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses,” which requires public business entities to disclose additional information about specific expense categories including employee compensation, depreciation, intangible asset amortization, etc., as well as qualitative descriptions of certain expenses, in the notes to the financial statements. This guidance is effective for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027. The guidance is to be applied either prospectively or retrospectively. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements. Induced Conversions of Convertible Debt Instruments In November 2024, the FASB issued ASU No. 2024-04, “Debt – Debt with Conversion and Other Options (Subtopic 470-20): Induced Conversions of Convertible Debt Instruments” to clarify the requirements for determining whether certain settlements of convertible debt instruments should be accounted for as an induced conversion. The Company adopted ASU No. 2024-04 as of January 1, 2026. Adoption of this standard did not impact the Company’s consolidated financial statements. Determining the Accounting Acquirer in the Acquisition of a Variable Interest Entity In May 2025, the FASB issued ASU No. 2025-03, “Business Combinations (Topic 805) and Consolidation (Topic 810): Determining the Accounting Acquirer in the Acquisition of a Variable Interest Entity” which requires an entity involved in an acquisition transaction affected by primarily exchanging equity interests when the legal acquirer is a variable interest entity that meets the definition of a business, to consider specific factors when determining which entity is the accounting acquirer. This guidance is effective for fiscal years beginning after December 15, 2026, including interim periods therein, and is to be applied on a prospective basis to any acquisition transaction that occurs after the initial application date. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements. Measurement of Credit Losses for Accounts Receivable and Contract Assets In July 2025, the FASB issued ASU No. 2025-05, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses for Accounts Receivable and Contract Assets” which provides public business entities with a practical expedient—and private companies an accounting policy election—when estimating expected credit losses for current accounts receivable and current contract assets arising from transactions accounted for under Topic Accounting Standards Codification (“ASC”) 606. In developing reasonable and supportable forecasts—if an entity elects the practical expedient—it assumes that current conditions as of the balance sheet date do not change for the remaining life of the assets in scope. The Company adopted ASU No. 2025-05 as of January 1, 2026. Adoption of this standard did not impact the Company’s consolidated financial statements as the Company did not elect the practical expedient. Targeted Improvements to the Accounting for Internal-Use Software In September 2025, the FASB issued ASU No. 2025-06, “Intangibles – Goodwill and Other Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software” which removes all references to prescriptive and sequential software development stages, instead requiring capitalization of software costs when management has authorized and committed to funding the software project, and it is probable that the project will be completed and the software will be used to perform the function needed. This guidance is effective for fiscal years beginning after December 15, 2027, including interim periods therein, and can be applied either prospectively, retrospectively, or through a modified transition approach. Early adoption is permitted at the beginning of an annual reporting period. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements. Derivatives Scope Refinements & Scope Clarification for Share-Based Noncash Consideration In September 2025, the FASB issued ASU No. 2025-07, “Derivatives and Hedging (Topic 815) and Revenue from Contracts with Customers (Topic 606): Derivatives Scope Refinements and Scope Clarification for Share-Based Noncash Consideration from a Customer in a Revenue Contract” which covers two separate issues. Issue 1 adds a scope exception to exclude from derivative accounting non-exchange-traded contracts with underlyings linked to the occurrence or nonoccurrence of an event. Issue 2 clarifies that entities should apply the guidance in ASC 606—on noncash consideration—to a contract with share-based noncash consideration from a customer for the transfer of goods or services. This guidance is effective for fiscal years beginning after December 15, 2026, including interim periods therein, and can be applied either on a prospective or modified retrospective basis. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements. Credit Losses - Purchased Loans In November 2025, the FASB issued ASU No. 2025-08, “Financial Instruments - Credit Losses (Topic 326): Purchased Loans” which expands the population of acquired financial assets subject to the gross-up approach under Topic 326. Loans—excluding credit cards—acquired without credit deterioration and deemed “seasoned” are purchased seasoned loans and accounted for using the gross-up approach at acquisition. The Company early adopted ASU No. 2025-08 as of January 1, 2026. Adoption of this standard did not impact the Company’s consolidated financial statements in the current period as no acquisition occurred. Hedge Accounting Improvements In November 2025, the FASB issued ASU No. 2025-09, “Derivatives and Hedging (Topic 815): Hedge Accounting Improvements” which clarifies certain aspects of the guidance on hedge accounting and addresses several incremental hedge accounting issues arising from the global reference rate reform initiative. For public business entities, this guidance is effective for fiscal years beginning after December 15, 2026, including interim periods therein, and should be applied on a prospective basis for all hedging relationships. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements. Interim Reporting Scope Improvements In December 2025, the FASB issued ASU No. 2025-11, “Interim Reporting (Topic 270): Narrow-Scope Improvements” which clarifies interim disclosure requirements and the applicability of Topic 270, resulting in a comprehensive list of interim disclosures required by GAAP. For public business entities, this guidance is effective for fiscal years beginning after December 15, 2027, including interim periods therein, and can be applied either on a prospective or retrospective basis. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements.
Cash and Cash Equivalents	For purposes of the Consolidated Statements of Cash Flows, the Company considers cash and cash equivalents to include cash on hand, cash items in the process of collection, non-interest bearing amounts due from correspondent banks, federal funds sold and securities purchased under resale agreements with original maturities of three months or less. These items are included within the Company’s Consolidated Statements of Condition as cash and due from banks, and federal funds sold and securities purchased under resale agreements.

Basis of Presentation (Policies)

3 Months Ended

Mar. 31, 2026

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The interim consolidated financial statements of Wintrust Financial Corporation and its subsidiaries (collectively, “Wintrust” or the “Company”) presented herein are unaudited, but in the opinion of management, reflect all necessary adjustments of a normal or recurring nature for a fair presentation of results as of the dates and for the periods covered by the interim consolidated financial statements.

The accompanying interim consolidated financial statements are unaudited and do not include information or footnotes necessary for a complete presentation of financial condition, results of operations or cash flows in accordance with U.S. generally accepted accounting principles (“GAAP”). The interim unaudited consolidated financial statements should be read in conjunction with the consolidated financial statements and notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2025 (“2025 Form 10-K”). Operating results reported for the period are not necessarily indicative of the results which may be expected for the entire year. Reclassifications of certain prior period amounts have been made to conform to the current period presentation.

The preparation of the financial statements requires management to make estimates, assumptions and judgments that affect the reported amounts of assets and liabilities. Management believes that the estimates made are reasonable; however, changes in estimates may be required if economic or other conditions develop differently from management’s expectations. Certain policies and accounting principles inherently have a greater reliance on the use of estimates, assumptions and judgments and as such have a greater possibility of producing results that could be materially different than originally reported. Management views critical accounting policies to be those which are highly dependent on subjective or complex judgments, estimates and assumptions, and where changes in those estimates and assumptions could have a significant impact on the financial statements. Management currently views the determination of the allowance for credit losses, including the allowance for loan losses, the allowance for unfunded commitment losses and the allowance for held-to-maturity securities losses, estimations of fair value, the valuations required for impairment testing of goodwill, the valuation and accounting for derivative instruments and income taxes as the accounting areas that require the most subjective and complex judgments, and as such could be the most subject to revision as new information becomes available. Descriptions of the Company’s significant accounting policies are included in Note (1) “Summary of Significant Accounting Policies” of the 2025 Form 10-K. In preparation of these financial statements, subsequent events were evaluated through the time the financial statements were issued. Financial statements are considered issued when they are widely distributed to all shareholders and other financial statement users or filed with the SEC.

Recent Accounting Developments

Disaggregation of Income Statement Expenses

In November 2024, the FASB issued Accounting Standards Update (“ASU”) No. 2024-03, “Income Statement – Reporting Comprehensive Income – Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses,” which requires public business entities to disclose additional information about specific expense categories including employee compensation, depreciation, intangible asset amortization, etc., as well as qualitative descriptions of certain expenses, in the notes to the financial statements. This guidance is effective for fiscal years beginning after December 15, 2026, and interim periods within fiscal years beginning after December 15, 2027. The guidance is to be applied either prospectively or retrospectively. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements.

Induced Conversions of Convertible Debt Instruments

In November 2024, the FASB issued ASU No. 2024-04, “Debt – Debt with Conversion and Other Options (Subtopic 470-20): Induced Conversions of Convertible Debt Instruments” to clarify the requirements for determining whether certain settlements of convertible debt instruments should be accounted for as an induced conversion. The Company adopted ASU No. 2024-04 as of January 1, 2026. Adoption of this standard did not impact the Company’s consolidated financial statements.

Determining the Accounting Acquirer in the Acquisition of a Variable Interest Entity

In May 2025, the FASB issued ASU No. 2025-03, “Business Combinations (Topic 805) and Consolidation (Topic 810): Determining the Accounting Acquirer in the Acquisition of a Variable Interest Entity” which requires an entity involved in an acquisition transaction affected by primarily exchanging equity interests when the legal acquirer is a variable interest entity that meets the definition of a business, to consider specific factors when determining which entity is the accounting acquirer. This guidance is effective for fiscal years beginning after December 15, 2026, including interim periods therein, and is to be applied on a prospective basis to any acquisition transaction that occurs after the initial application date. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements.

Measurement of Credit Losses for Accounts Receivable and Contract Assets

In July 2025, the FASB issued ASU No. 2025-05, “Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses for Accounts Receivable and Contract Assets” which provides public business entities with a practical expedient—and private companies an accounting policy election—when estimating expected credit losses for current accounts receivable and current contract assets arising from transactions accounted for under Topic Accounting Standards Codification (“ASC”) 606. In developing reasonable and supportable forecasts—if an entity elects the practical expedient—it assumes that current conditions as of the balance sheet date do not change for the remaining life of the assets in scope. The Company adopted ASU No. 2025-05 as of January 1, 2026. Adoption of this standard did not impact the Company’s consolidated financial statements as the Company did not elect the practical expedient.

Targeted Improvements to the Accounting for Internal-Use Software

In September 2025, the FASB issued ASU No. 2025-06, “Intangibles – Goodwill and Other Internal-Use Software (Subtopic 350-40): Targeted Improvements to the Accounting for Internal-Use Software” which removes all references to prescriptive and sequential software development stages, instead requiring capitalization of software costs when management has authorized and committed to funding the software project, and it is probable that the project will be completed and the software will be used to perform the function needed. This guidance is effective for fiscal years beginning after December 15, 2027, including interim periods therein, and can be applied either prospectively, retrospectively, or through a modified transition approach. Early adoption is permitted at the beginning of an annual reporting period. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements.

Derivatives Scope Refinements & Scope Clarification for Share-Based Noncash Consideration

In September 2025, the FASB issued ASU No. 2025-07, “Derivatives and Hedging (Topic 815) and Revenue from Contracts with Customers (Topic 606): Derivatives Scope Refinements and Scope Clarification for Share-Based Noncash Consideration from a Customer in a Revenue Contract” which covers two separate issues. Issue 1 adds a scope exception to exclude from derivative accounting non-exchange-traded contracts with underlyings linked to the occurrence or nonoccurrence of an event. Issue 2 clarifies that entities should apply the guidance in ASC 606—on noncash consideration—to a contract with share-based noncash consideration from a customer for the transfer of goods or services. This guidance is effective for fiscal years beginning after December 15, 2026, including interim periods therein, and can be applied either on a prospective or modified retrospective basis. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements.

Credit Losses - Purchased Loans

In November 2025, the FASB issued ASU No. 2025-08, “Financial Instruments - Credit Losses (Topic 326): Purchased Loans” which expands the population of acquired financial assets subject to the gross-up approach under Topic 326. Loans—excluding credit cards—acquired without credit deterioration and deemed “seasoned” are purchased seasoned loans and accounted for using the gross-up approach at acquisition. The Company early adopted ASU No. 2025-08 as of January 1, 2026. Adoption of this standard did not impact the Company’s consolidated financial statements in the current period as no acquisition occurred.

Hedge Accounting Improvements

In November 2025, the FASB issued ASU No. 2025-09, “Derivatives and Hedging (Topic 815): Hedge Accounting Improvements” which clarifies certain aspects of the guidance on hedge accounting and addresses several incremental hedge accounting issues arising from the global reference rate reform initiative. For public business entities, this guidance is effective for fiscal years beginning after December 15, 2026, including interim periods therein, and should be applied on a prospective basis for all hedging relationships. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements.

Interim Reporting Scope Improvements

In December 2025, the FASB issued ASU No. 2025-11, “Interim Reporting (Topic 270): Narrow-Scope Improvements” which clarifies interim disclosure requirements and the applicability of Topic 270, resulting in a comprehensive list of interim disclosures required by GAAP. For public business entities, this guidance is effective for fiscal years beginning after December 15, 2027, including interim periods therein, and can be applied either on a prospective or retrospective basis. Early adoption is permitted. The Company is currently evaluating the impact of adopting this new guidance on the consolidated financial statements.

Cash and Cash Equivalents

For purposes of the Consolidated Statements of Cash Flows, the Company considers cash and cash equivalents to include cash on hand, cash items in the process of collection, non-interest bearing amounts due from correspondent banks, federal funds sold and securities purchased under resale agreements with original maturities of three months or less. These items are included within the Company’s Consolidated Statements of Condition as cash and due from banks, and federal funds sold and securities purchased under resale agreements.