General (Policies)	3 Months Ended
Mar. 31, 2025
Accounting Policies [Abstract]
Basis of Presentation	The Condensed Consolidated Financial Statements include the accounts of CNA Financial Corporation (CNAF) and its subsidiaries. Collectively, CNAF and its subsidiaries are referred to as CNA or the Company. Loews Corporation (Loews) owned approximately 92% of the outstanding common stock of CNAF as of March 31, 2025.
Use of Estimates	The preparation of Condensed Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the Condensed Consolidated Financial Statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates.The interim financial data as of March 31, 2025 and for the three months ended March 31, 2025 and 2024 is unaudited. However, in the opinion of management, the interim data includes all adjustments, including normal recurring adjustments, necessary for a fair statement of the Company's results for the interim periods in accordance with GAAP. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the full year.
Accounting Standards Pending Adoption	Accounting Standards Pending Adoption In December 2023, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. The updated accounting guidance requires expanded income tax disclosures, including the disaggregation of existing disclosures related to the tax rate reconciliation and income taxes paid. The guidance is effective for annual periods beginning after December 15, 2024. Therefore, for the Company, the guidance is effective for the Annual Report on Form 10-K for the year ended December 31, 2025. In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. The updated accounting guidance requires disaggregated disclosure of specified expense categories. The guidance also requires disclosure of total selling expenses and how the Company defines selling expenses. The guidance is effective for fiscal years beginning after December 15, 2026, and interim periods within annual periods beginning after December 15, 2027. Prospective application is required, with retrospective application permitted. The Company is currently evaluating the effect the updated guidance will have on the Company's financial statement disclosures.

General (Policies)

3 Months Ended

Mar. 31, 2025

The Condensed Consolidated Financial Statements include the accounts of CNA Financial Corporation (CNAF) and its subsidiaries. Collectively, CNAF and its subsidiaries are referred to as CNA or the Company. Loews Corporation (Loews) owned approximately 92% of the outstanding common stock of CNAF as of March 31, 2025.

Use of Estimates

The preparation of Condensed Consolidated Financial Statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the Condensed Consolidated Financial Statements and the reported amounts of revenues and expenses during the reporting period. Actual results may differ from those estimates.The interim financial data as of March 31, 2025 and for the three months ended March 31, 2025 and 2024 is unaudited. However, in the opinion of management, the interim data includes all adjustments, including normal recurring adjustments, necessary for a fair statement of the Company's results for the interim periods in accordance with GAAP. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the full year.

Accounting Standards Pending Adoption

In December 2023, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures. The updated accounting guidance requires expanded income tax disclosures, including the disaggregation of existing disclosures related to the tax rate reconciliation and income taxes paid. The guidance is effective for annual periods beginning after December 15, 2024. Therefore, for the Company, the guidance is effective for the Annual Report on Form 10-K for the year ended December 31, 2025.

In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses. The updated accounting guidance requires disaggregated disclosure of specified expense categories. The guidance also requires disclosure of total selling expenses and how the Company defines selling expenses. The guidance is effective for fiscal years beginning after December 15, 2026, and interim periods within annual periods beginning after December 15, 2027. Prospective application is required, with retrospective application permitted. The Company is currently evaluating the effect the updated guidance will have on the Company's financial statement disclosures.