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| **Organization, Consolidation and Presentation of Financial Statements [Abstract]**          | Â                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] | 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 (CIC), Continental Assurance Company (CAC) and CNA Surety Corporation (CNA Surety).  Loews Corporation (Loews) owned approximately 90% of the outstanding common stock of CNAF as of June 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 June 30, 2011 and for the three and six months ended June 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.CNA SuretyOn June 10, 2011, CNA completed its previously announced acquisition of the noncontrolling interest of 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.  For the three and six months ended June 30, 2011, net income attributable to the noncontrolling interest in CNA Surety through the acquisition date of June 10, 2011 was $4 million and $12 million and is reflected on the Condensed Consolidated Statement of Operations.  For the three and six months ended June 30, 2010, net income attributable to the noncontrolling interest in CNA Surety was $11 million and $19 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. For the six months ended June 30, 2011, there was no significant change in the Company’s allowance for uncollectible reinsurance receivables. |

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The entire disclosure for organization, consolidation and basis of presentation of financial statements disclosure.
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