| **General**                                                                         | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   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| **Organization, Consolidation and Presentation of Financial Statements [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  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| General                                                                             | GeneralBasis of PresentationThe Condensed Consolidated Financial Statements (Unaudited) include the accounts of CNA Financial Corporation (CNAF) and its controlled subsidiaries. Collectively, CNAF and its controlled subsidiaries are referred to as CNA or the Company. CNA’s property and casualty and remaining life and group insurance operations are primarily conducted by Continental Casualty Company (CCC), The Continental Insurance Company, Western Surety Company and Continental Assurance Company.  Loews Corporation (Loews) owned approximately 90% of the outstanding common stock of CNAF as of September 30, 2011.The accompanying Condensed Consolidated Financial Statements have been prepared in conformity with accounting principles generally accepted in the United States of America (GAAP). Certain financial information that is normally included in annual financial statements, including certain financial statement notes, prepared in accordance with GAAP, is not required for interim reporting purposes and has been condensed or omitted. These statements should be read in conjunction with the Consolidated Financial Statements and notes thereto included in CNAF’s Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC) for the year ended December 31, 2010, including the summary of significant accounting policies in Note A. 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 periods. Actual results may differ from those estimates.The interim financial data as of September 30, 2011 and for the three and nine months ended September 30, 2011 and 2010 is unaudited. However, in the opinion of management, the interim data includes all adjustments, consisting of normal recurring accruals, necessary for a fair statement of the Company’s results for the interim periods. The results of operations for the interim periods are not necessarily indicative of the results to be expected for the full year. Intercompany amounts have been eliminated.The Company has historically reported certain run-off insurance and reinsurance operations acquired in its merger with The Continental Corporation in 1995 as discontinued operations. Due to the immateriality of the remaining liabilities, effective in the third quarter of 2011, the Company is no longer reporting these run-off operations as discontinued operations.First Insurance Company of HawaiiThe Company owns 50% of the common stock of First Insurance Company of Hawaii (FICOH).  On August 11, 2011, CNA announced the sale of its noncontrolling interest in FICOH to Tokio Marine & Nichido Fire Insurance Co., Ltd., the other 50% shareholder.  The sale, which is subject to regulatory approval, is expected to close in the fourth quarter of 2011 and result in a modest gain.  The Company previously anticipated recovering the undistributed earnings of FICOH at a dividend tax rate.  As a result of the pending sale, the Company has increased income tax expense by $22 million to reflect the statutory tax rate.CNA Surety CorporationOn June 10, 2011, CNA completed its previously announced acquisition of the noncontrolling interest of CNA Surety Corporation (CNA Surety).  Previously the Company owned approximately 61% of the outstanding publicly-traded common stock of CNA Surety.  CNA Surety is now a wholly-owned subsidiary of CCC, and, effective after the close of the stock market on June 10, 2011, trading in CNA Surety common stock ceased. The aggregate purchase price was approximately $475 million, based on the offer price of $26.55 per share and inclusive of the retirement of CNA Surety employee stock options.  The amount paid to acquire the common stock of CNA Surety not owned by the Company in excess of the closing date noncontrolling interest included in the Company's equity of $434 million was reflected as an adjustment to Additional Paid-in Capital and Accumulated Other Comprehensive Income on the Condensed Consolidated Statement of Equity.  During 2011, net income attributable to the noncontrolling interest in CNA Surety through the acquisition date of June 10, 2011 was $12 million and is reflected on the Condensed Consolidated Statement of Operations.  For the three and nine months ended September 30, 2010, net income attributable to the noncontrolling interest in CNA Surety was $11 million and $30 million.Reinsurance ReceivablesThe Company has established an allowance for uncollectible reinsurance receivables which relates to both amounts already billed on ceded paid losses as well as ceded reserves that will be billed when losses are paid in the future. The allowance for uncollectible reinsurance receivables is estimated on the basis of periodic evaluations of balances due from reinsurers, reinsurer creditworthiness, management’s experience and current economic conditions. Financial strength ratings are updated and reviewed on an annual basis or sooner if the Company becomes aware of significant changes related to a reinsurer. Because billed receivables are less than 5% of total reinsurance receivables, the age of the reinsurance receivables related to paid losses is not a significant input into the allowance analysis. During the three months ended September 30, 2011, the Company reduced its allowance for uncollectible reinsurance receivables by $15 million arising from a change in estimate.  The additional reduction in the allowance primarily related to write-offs of reinsurance receivable balances. Accounting for Costs Associated with Acquiring or Renewing Insurance ContractsIn October 2010, the FASB issued updated accounting guidance which limits the capitalization of costs incurred to acquire or renew insurance contracts to those that are incremental direct costs of successful contract acquisitions.  The updated accounting guidance is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2011 with prospective or retrospective application allowed.  The Company intends to adopt this updated accounting guidance retrospectively and is currently assessing the impact it will have on its financial condition and results of operations.  The Company preliminarily estimates that amounts capitalized under the current accounting guidance as of September 30, 2011 would be approximately $75 million to $130 million less under the updated guidance.  Any reduction of capitalized costs will also necessitate a change in related deferred tax balances. |

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| - Definition
The entire disclosure for the general note to the financial statements for the reporting entity which may include, descriptions of the basis of presentation, business description, significant accounting policies, consolidations, reclassifications, new pronouncements not yet adopted and changes in accounting principles.
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