| **Claim and Claim Adjustment Expense Reserves** | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 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| **Insurance Loss Reserves [Abstract]**          |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  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| Claim and Claim Adjustment Expense Reserves     | Note F. Claim and Claim Adjustment Expense ReservesThe Company's property and casualty insurance claim and claim adjustment expense reserves represent the estimated amounts necessary to resolve all outstanding claims, including IBNR claims as of the reporting date.  The Company's reserve projections are based primarily on detailed analysis of the facts in each case, the Company's experience with similar cases and various historical development patterns.  Consideration is given to such historical patterns as field reserving trends and claims settlement practices, loss payments, pending levels of unpaid claims and product mix, as well as court decisions, economic conditions including inflation, and public attitudes.  All of these factors can affect the estimation of claim and claim adjustment expense reserves.Establishing claim and claim adjustment expense reserves, including claim and claim adjustment expense reserves for catastrophic events that have occurred, is an estimation process.  Many factors can ultimately affect the final settlement of a claim and, therefore, the necessary reserve.  Changes in the law, results of litigation, medical costs, the cost of repair materials and labor rates can all affect ultimate claim costs.  In addition, time can be a critical part of reserving determinations since the longer the span between the incidence of a loss and the payment or settlement of the claim, the more variable the ultimate settlement amount can be.  Accordingly, short-tail claims, such as property damage claims, tend to be more reasonably estimable than long-tail claims, such as workers' compensation, general liability and professional liability claims.  Adjustments to prior year reserve estimates, if necessary, are reflected in the results of operations in the period that the need for such adjustments is determined.  There can be no assurance that the Company's ultimate cost for insurance losses will not exceed current estimates.Catastrophes are an inherent risk of the property and casualty insurance business and have contributed to material period-to-period fluctuations in the Company's results of operations and/or equity.  The Company reported catastrophe losses, net of reinsurance, of $56 million and $130 million for the three and six months ended June 30, 2014.  Catastrophe losses in 2014 related primarily to U.S. weather-related events. The Company reported catastrophe losses, net of reinsurance, of $65 million and $104 million for the three and six months ended June 30, 2013. Net Prior Year Development The following tables and discussion include the net prior year development recorded for CNA Specialty, CNA Commercial, Hardy and Corporate & Other Non-Core segments.Net Prior Year DevelopmentThree months ended June 30, 2014         (In millions)CNASpecialty CNA Commercial Hardy Corporate & OtherNon-Core TotalPretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development$(55) $79 $— $— $24Pretax (favorable) unfavorable premium development(1) (5) 4 — (2)Total pretax (favorable) unfavorable net prior year development$(56) $74 $4 $— $22Three months ended June 30, 2013         (In millions)CNASpecialty CNA Commercial Hardy Corporate & Other Non-Core TotalPretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development$(41) $27 $12 $(3) $(5)Pretax (favorable) unfavorable premium development(5) (5) 2 — (8)Total pretax (favorable) unfavorable net prior year development$(46) $22 $14 $(3) $(13)Six months ended June 30, 2014         (In millions)CNA Specialty CNA Commercial Hardy Corporate & OtherNon-Core TotalPretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development$(57) $96 $10 $— $49Pretax (favorable) unfavorable premium development(9) (24) — — (33)Total pretax (favorable) unfavorable net prior year development$(66) $72 $10 $— $16Six months ended June 30, 2013         (In millions)CNA Specialty CNA Commercial Hardy Corporate & OtherNon-Core TotalPretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development$(56) $16 $11 $(2) $(31)Pretax (favorable) unfavorable premium development(13) (15) 6 1 (21)Total pretax (favorable) unfavorable net prior year development$(69) $1 $17 $(1) $(52)CNA SpecialtyThe following table provides further detail of the net prior year claim and allocated claim adjustment expense reserve development (development) recorded for the CNA Specialty segment for the three and six months ended June 30, 2014 and 2013.Periods ended June 30Three Months Six Months(In millions)2014 2013 2014 2013Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development:       Medical Professional Liability$1 $(17) $2 $(20)Other Professional Liability and Management Liability(58) (23) (64) (24)Surety— 1 1 2Warranty— — — —Other2 (2) 4 (14)Total pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development$(55) $(41) $(57) $(56)Three Months2014Favorable development for other professional liability and management liability was primarily related to favorable outcomes on individual large claims in accident years 2009 and prior, which contributed to a lower estimate of ultimate severity.  Additionally, there was better than expected severity in accident years 2008 through 2011.  2013Favorable development for medical professional liability was primarily due to a decrease in incurred loss severity in accident years 2009 and prior.Overall, favorable development for other professional liability and management liability was related to better than expected loss emergence in accident years 2007 through 2009.  Unfavorable development was recorded in accident years 2010 through 2012 related to an increase in severity.Six Months2014Favorable development for other professional liability and management liability was primarily related to favorable outcomes on individual large claims in accident years 2009 and prior, which contributed to a lower estimate of ultimate severity.  Additionally, there was better than expected severity in accident years 2008 through 2011.  2013Overall, favorable development for medical professional liability reflects favorable experience in accident years 2009 and prior.  Unfavorable development was recorded for accident years 2010 and 2011 due to higher than expected large loss activity.Overall, favorable development for other professional liability and management liability was related to better than expected loss emergence in accident years 2007 through 2009.  Unfavorable development was recorded in accident years 2010 through 2012 related to an increase in severity.Favorable development for other coverages was primarily due to better than expected loss emergence in property coverages in accident years 2010 and subsequent.CNA CommercialThe following table provides further detail of the development recorded for the CNA Commercial segment for the three and six months ended June 30, 2014 and 2013.  The majority of the 2014 unfavorable development relates to business classes which the Company has exited, but also includes Small Business where the Company is taking underwriting actions in an effort to improve profitability.Periods ended June 30Three Months Six Months(In millions)2014 2013 2014 2013Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development:       Commercial Auto$20 $2 $40 $(3)General Liability30 15 25 (6)Workers' Compensation40 45 50 70Property and Other(11) (35) (19) (45)Total pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development$79 $27 $96 $16Three Months2014Unfavorable development for commercial auto was primarily related to higher than expected frequency of large losses in accident years 2010 through 2013. Unfavorable development for general liability was primarily related to higher than expected severity in accident years 2009 through 2011.  In addition, there was higher than expected severity in accident year 2013 related to Small Business.Unfavorable development for workers’ compensation was primarily due to higher than expected severity related to Defense Base Act contractors in accident years 2012 and 2013.  Favorable development for property and other first-party coverages was recorded in accident years 2012 and prior, primarily related to fewer claims than expected and favorable individual claim settlements. 2013Unfavorable development for general liability coverages was primarily related to increased incurred loss severity in accident years 2010 through 2012.Unfavorable development for workers' compensation was primarily in response to legislation enacted during 2013 related to the New York Fund for Reopened Cases.  The law change necessitated an increase in reserves as re-opened workers' compensation claims can no longer be turned over to the state for handling and payment after December 31, 2013.Favorable development for property and other coverages was primarily related to favorable outcomes on litigated catastrophe claims in accident years 2005 and 2010 and favorable loss emergence on non-catastrophe losses in accident year 2012.Six Months2014Unfavorable development for commercial auto was primarily related to higher than expected frequency of large losses in accident years 2010 through 2013.  Additionally, unfavorable development was recorded for higher than expected frequency in accident years 2012 and 2013 and higher than expected severity in accident years 2010 and 2011.Unfavorable development for general liability was primarily related to higher than expected severity in accident years 2009 through 2011.  In addition, there was higher than expected severity in accident year 2013 related to Small Business.Unfavorable development for workers’ compensation was primarily due to higher than expected severity related to Defense Base Act contractors in accident years 2012 and 2013 and the recognition of losses related to favorable premium development in accident year 2013. Favorable development for property and other first-party coverages was recorded in accident years 2012 and prior, primarily related to fewer claims than expected and favorable individual claim settlements.2013Overall, favorable development for general liability coverages was primarily related to better than expected loss emergence in accident years 2002 and prior.  Unfavorable development was recorded in accident years 2010 through 2012 primarily related to increased incurred loss severity.Unfavorable development for workers' compensation was recorded in response to legislation in New York as discussed above.  Additional unfavorable development was primarily due to higher than expected large losses and increased severity in the state of California in accident year 2010.Favorable development for property and other coverages was primarily related to favorable outcomes on litigated catastrophe claims in accident years 2005 and 2010 and favorable loss emergence on non-catastrophe losses in accident year 2012.HardyThe following table provides further detail of the development recorded for the Hardy segment for the three and six months ended June 30, 2014 and 2013.Periods ended June 30Three Months Six Months(In millions)2014 2013 2014 2013Pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development:       Marine and Aviation$1 $4 $6 $3Non-Marine Property3 7 1 7Property Treaty(2) 2 (4) 2Specialty(2) (1) (3) (1) Commutations— — 10 —Total pretax (favorable) unfavorable net prior year claim and allocated claim adjustment expense reserve development$— $12 $10 $11Three Months2013Unfavorable development for non-marine property was primarily due to 2011 catastrophe events, including the Thailand floods and the New Zealand Lyttelton earthquake.Six Months2014Reinsurance commutations in the first quarter of 2014 reduced ceded losses from prior years. Overall the commutations increased net operating income because of the release of the related allowance for uncollectible reinsurance. 2013Unfavorable development for non-marine property was primarily due to 2011 catastrophe events, including the Thailand floods and the New Zealand Lyttelton earthquake. |

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