|**Stockholders' Equity and Statutory Accounting Practices**            | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                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|**Stockholders' Equity and Statutory Accounting Practices [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
|Stockholders' Equity And Statutory Accounting Practices                | NoteL. Stockholders’ Equity and Statutory Accounting Practices2008 Senior PreferredIn 2008, the Company issued, and Loews purchased,$1.25 billionof CNAF non-voting cumulative senior preferred stock, which was approved by a special review committee of independent members of CNAF's Board of Directors.  As of December 31, 2010, the preferred stock was redeemed in full.CNAF used the majority of the proceeds from the 2008 Senior Preferred to increase the statutory surplus of its principal insurance subsidiary, CCC, through the purchase of a$1.0 billionsurplus note of CCC. Surplus notes are financial instruments with a stated maturity date and scheduled interest payments, issued by insurance enterprises with the approval of the insurer’s domiciliary state. Surplus notes are treated as capital under statutory accounting. All payments of interest and principal on this note are subject to the prior approval of the Illinois Department of Insurance (the Department).The surplus note of CCC has a term of 30 years and accrues interest at a rate of 10% per year. Interest on the note is payable quarterly.In 2011 and 2010, the Company received regulatory approval from the Department for CCC to repay$250 millionand$500 millionof the $1.0 billion surplus note to CNAF, leaving an outstanding balance of$250 millionas of December 31, 2011.Common Stock DividendsDividends of$0.40per share on CNA's common stock were declared and paid in 2011. No common stock dividends were declared or paid in2010or2009.Statutory Accounting Practices (Unaudited)CNAF’s domestic insurance subsidiaries maintain their accounts in conformity with accounting practices prescribed or permitted by insurance regulatory authorities, which vary in certain respects from GAAP. In converting from statutory accounting principles to GAAP, the more significant adjustments include deferral of policy acquisition costs and the inclusion of net unrealized holding gains or losses in stockholders’ equity relating to certain fixed maturity securities.CNAF’s insurance subsidiaries are domiciled in various jurisdictions. These subsidiaries prepare statutory financial statements in accordance with accounting practices prescribed or permitted by the respective jurisdictions’ insurance regulators. Domestic prescribed statutory accounting practices are set forth in a variety of publications of the National Association of Insurance Commissioners (NAIC) as well as state laws, regulations and general administrative rules.CNAF’s ability to pay dividends and other credit obligations is significantly dependent on receipt of dividends from its subsidiaries. The payment of dividends to CNAF by its insurance subsidiaries without prior approval of the insurance department of each subsidiary’s domiciliary jurisdiction is limited by formula. Dividends in excess of these amounts are subject to prior approval by the respective state insurance departments.Dividends from CCC are subject to the insurance holding company laws of the State of Illinois, the domiciliary state of CCC. Under these laws, ordinary dividends, or dividends that do not require prior approval by the Department, may be paid only from earned surplus, which is calculated by removing unrealized gains from unassigned surplus. As ofDecember 31, 2011, CCC is in a positive earned surplus position, enabling CCC to pay approximately$990 millionof dividend payments during2012that would not be subject to the Department’s prior approval. The actual level of dividends paid in any year is determined after an assessment of available dividend capacity, holding company liquidity and cash needs as well as the impact the dividends will have on the statutory surplus of the applicable insurance company.CNAF’s domestic insurance subsidiaries are subject to risk-based capital requirements. Risk-based capital is a method developed by the NAIC to determine the minimum amount of statutory capital appropriate for an insurance company to support its overall business operations in consideration of its size and risk profile. The formula for determining the amount of risk-based capital specifies various factors, weighted based on the perceived degree of risk, which are applied to certain financial balances and financial activity. The adequacy of a company's actual capital is evaluated by a comparison to the risk-based capital results, as determined by the formula. Companies below minimum risk-based capital requirements are classified within certain levels, each of which requires specified corrective action. As ofDecember 31, 2011and2010, all of CNAF’s domestic insurance subsidiaries exceeded the minimum risk-based capital requirements.Subsidiaries with insurance operations outside the United States are also subject to insurance regulation in the countries in which they operate. The Company has legal entity and branch operations in other countries, primarily the United Kingdom, Canada and Bermuda. CNAF’s foreign legal entities and branch met or exceeded regulatory capital requirements.Combined statutory capital and surplus and net income (loss), determined in accordance with accounting practices prescribed or permitted by insurance regulatory authorities for the Combined Continental Casualty Companies and the life company, were as follows.Statutory InformationStatutory Capital and SurplusStatutory Net Income (Loss)December 31Years ended December 31(In millions)2011 (b)20102011 (b)20102009Combined Continental Casualty Companies (a)$9,888$9,821$954$258$17Life company5194982986(65)________________(a)Represents the combined statutory surplus of CCC and its subsidiaries, including the Life company.(b)Preliminary.
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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|                                                                       | Statutory Capital and Surplus                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   
|                                                                       | December 31                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     
|(In millions)                                                          | 2011 (b)                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        
|Combined Continental Casualty Companies (a)                            | $                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|Life company                                                           | 519                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|(a)                                                                    | Represents the combined statutory surplus of CCC and its subsidiaries, including the Life company.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               
|(b)                                                                    | Preliminary.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   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