| **Benefit Plans**                                     | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         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| **Compensation and Retirement Disclosure [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         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| Benefit Plans                                         | Note J. Benefit PlansPension and Postretirement Health Care Benefit PlansCNA sponsors noncontributory defined benefit pension plans, primarily through the CNA Retirement Plan, covering certain eligible employees.  These plans are closed to new entrants.Effective January 1, 2000, the CNA Retirement Plan was closed to new participants.  Existing participants at that time were given a choice to either continue to accrue benefits under the CNA Retirement Plan or to cease accruals at December 31, 1999.  Employees who chose to continue to accrue benefits under the plan will receive a benefit based on their years of credited service and highest 60 months of compensation at termination.  Compensation is defined as regular salary, eligible bonuses and overtime. Employees who elected to cease accruals at December 31, 1999 received the present value of their accrued benefit in an accrued pension account that is credited with interest based on the annual rate of interest on 30-year Treasury securities. These employees also receive certain enhanced employer contributions in the CNA Savings and Capital Accumulation Plan.CNA's funding policy for defined benefit pension plans is to make contributions in accordance with applicable governmental regulatory requirements with consideration of the funded status of the plans.During 2014, the CNA Retirement Plan offered a limited-time lump sum settlement payment opportunity to the majority of the terminated vested participants of the plan.  The lump sum settlements reduce the Company’s risk and volatility related to funding the CNA Retirement Plan.  The number of participants that elected to accept the lump sum opportunity was approximately 20% of the then total participants in the plan.  The settlement payments of $253 million were made from CNA Retirement Plan assets.  The $84 million settlement charge recorded by the Company in the fourth quarter of 2014 represents recognition of a portion of the unrecognized actuarial losses previously reflected in AOCI.  This settlement charge is included in Other operating expenses within the Corporate & Other Non-Core segment. CNA provides certain health care benefits to eligible retired employees, their covered dependents and their beneficiaries primarily through the CNA Health and Group Benefits Program.  These postretirement benefits have largely been eliminated for active employees.In the second quarter of 2014, the Company eliminated certain postretirement medical benefits associated with the CNA Health and Group Benefits Program.  This change was a negative plan amendment which resulted in an $86 million curtailment gain reported in Other operating expenses within the Corporate & Other Non-Core segment.  In connection with the plan amendment, the Company remeasured the plan benefit obligation which resulted in a decrease in the discount rate used to determine the benefit obligation from 3.60% to 3.10%.The following table provides a reconciliation of benefit obligations and plan assets for the years ended December 31, 2014 and 2013.Funded Status Pension Benefits Postretirement Benefits(In millions)2014 2013 2014 2013Benefit obligation at January 1$2,943 $3,271 $40 $47Changes in benefit obligation:       Service cost9 12 — 1Interest cost132 121 1 1Participants' contributions— — 5 5Plan amendments(3) — (7) —Actuarial (gain) loss367 (289) 1 (3)Benefits paid(165) (165) (11) (12)Settlements(257) (8) — —Foreign currency translation and other(7) 1 — 1Benefit obligation at December 313,019 2,9432940Fair value of plan assets at January 12,656 2,425 — —Change in plan assets:       Actual return on plan assets216 311 — —Company contributions12 92 6 7Participants' contributions— — 5 5Benefits paid(165) (165) (11) (12)Settlements(257) (8) — —Foreign currency translation and other(6) 1 — —Fair value of plan assets at December 312,456 2,656 — —Funded status$(563) $(287) $(29) $(40)Amounts recognized on the Consolidated Balance Sheets at December 31:       Other assets$9 $9 $— $—Other liabilities(572) (296) (29) (40)Net amount recognized$(563) $(287) $(29) $(40)Amounts recognized in Accumulated other comprehensive income, not yet recognized in net periodic cost (benefit):       Prior service credit$— $— $(9) $(98)Net actuarial loss974 745 8 8Net amount recognized$974 $745 $(1) $(90)The accumulated benefit obligation for all defined benefit pension plans was $2,962 million and $2,889 million at December 31, 2014 and 2013.The components of net periodic cost (benefit) are presented in the following table.Net Periodic Cost (Benefit)Years ended December 31     (In millions)2014 2013 2012Pension cost (benefit)     Service cost$9 $12 $12Interest cost on projected benefit obligation132 121 135Expected return on plan assets(191) (181) (171)Amortization of net actuarial loss25 47 39Settlement loss84 3 —Net periodic pension cost (benefit)$59 $2 $15      Postretirement cost (benefit)     Service cost$— $1 $—Interest cost on projected benefit obligation1 1 2Amortization of prior service credit(10) (18) (18)Amortization of net actuarial loss1 2 1Curtailment gain(86)——Net periodic postretirement cost (benefit)$(94) $(14) $(15)The amounts recognized in Other comprehensive income are presented in the following table.Years ended December 31     (In millions)2014 2013 2012Pension and postretirement benefits     Amounts arising during the period$(337) $422 $(195)Curtailment and other(81) — —Settlement84 — —Reclassification adjustment relating to prior service credit(10) (18) (18)Reclassification adjustment relating to actuarial loss26 49 40Total increase (decrease) in Other comprehensive income$(318) $453 $(173)The table below presents the estimated amounts to be recognized from AOCI into net periodic cost (benefit) during 2015.(In millions) PensionBenefits Postretirement BenefitsAmortization of prior service credit $— $(2)Amortization of net actuarial loss 38 1Total estimated amounts to be recognized $38 $(1)Actuarial assumptions used for the CNA Retirement Plan and CNA Health and Group Benefits Program to determine benefit obligations are set forth in the following table.Actuarial Assumptions for Benefit ObligationsDecember 312014 2013Pension benefits   Discount rate3.850% 4.650%Expected long term rate of return7.500 7.500Rate of compensation increases3.920 3.990Postretirement benefits   Discount rate2.500% 3.600%Actuarial assumptions used for the CNA Retirement Plan and CNA Health and Group Benefits Program to determine net cost or benefit are set forth in the following table.Actuarial Assumptions for Net Cost or BenefitYears ended December 312014 2013 2012Pension benefits     Discount rate4.650% 3.800% 4.600%Expected long term rate of return7.500 7.750 8.000Rate of compensation increases3.990 4.066 4.125Postretirement benefits     Discount rate3.600%/3.100% 2.800% 3.750%In determining the expected long term rate of return on plan assets assumption for the CNA Retirement Plan, CNA considered the historical performance of the benefit plan investment portfolio as well as long term market return expectations based on the investment mix of the portfolio. The CNA Health and Group Benefits Program has limited its share of the health care trend rate to a cost-of-living adjustment of 4% per year.  For all participants, the employer subsidy on health care costs will not increase by more than 4% per year.  As a result, the assumed health care cost trend rate used in measuring the accumulated postretirement benefit obligation for the CNA Health and Group Benefits Program was 4% per year in 2014, 2013 and 2012.CNA employs a total return approach whereby a mix of equity, limited partnerships and fixed maturity securities are used to maximize the long term return of retirement plan assets for a prudent level of risk and to manage cash flows according to plan requirements.  The target allocation of plan assets is 40% to 60% invested in equity securities and limited partnerships, with the remainder primarily invested in fixed maturity securities.  The intent of this strategy is to minimize the Company's expense related to funding the plan by generating investment returns that exceed the growth of the plan liabilities over the long run.  Risk tolerance is established after careful consideration of the plan liabilities, plan funded status and corporate financial conditions.  In addition, alternative investments, including limited partnerships, are used to enhance risk adjusted long term returns while improving portfolio diversification.  At December 31, 2014, the plan had committed approximately $107 million to future capital calls from various third-party limited partnership investments in exchange for an ownership interest in the related partnerships. Derivatives may be used to gain market exposure in an efficient and timely manner.  Investment risk is measured and monitored on an ongoing basis through annual liability measurements, periodic asset/liability studies and quarterly investment portfolio reviews.Pension plan assets measured at fair value on a recurring basis as well as cash are summarized below. December 31, 2014        (In millions) Level 1 Level 2 Level 3 Total Assets at Fair ValueAssets        Fixed maturity securities:        Corporate and other bonds $— $463 $15 $478States, municipalities and political subdivisions — 80 — 80Asset-backed:        Residential mortgage-backed — 123 — 123Commercial mortgage-backed — 75 — 75Other asset-backed — 12 — 12Total asset-backed — 210 — 210U.S. Treasury and obligations of government-sponsored enterprises 25 — — 25Total fixed maturity securities 25 753 15 793Equity securities 389 118 — 507Derivative financial instruments 1 — — 1Short term investments 33 101 — 134Limited partnerships:        Hedge funds — 562 303 865Private equity — — 113 113Total limited partnerships — 562 416 978Other assets — 30 — 30Cash 13 — — 13Total assets $461 $1,564 $431 $2,456December 31, 2013        (In millions) Level 1 Level 2 Level 3 Total Assets at Fair ValueAssets        Fixed maturity securities:        Corporate and other bonds $— $505 $15 $520States, municipalities and political subdivisions — 73 — 73Asset-backed:        Residential mortgage-backed — 130 — 130Commercial mortgage-backed — 106 — 106   Other asset-backed — 12 — 12Total asset-backed — 248 — 248Total fixed maturity securities — 826 15 841Equity securities 480 117 8 605Derivative financial instruments 2 — — 2Short term investments 45 49 — 94Limited partnerships:       Hedge funds — 647 322 969Private equity — — 114 114Total limited partnerships — 647 436 1,083Other assets — 31 — 31Total assets $527 $1,670 $459 $2,656The limited partnership investments are recorded at fair value, which represents the plan's share of net asset value of each partnership, as determined by the General Partner.  Level 2 includes limited partnership investments which can be redeemed at net asset value in 90 days or less.  Level 3 includes limited partnership investments with withdrawal provisions greater than 90 days, or for which withdrawals are not permitted until the termination of the partnership.  Within hedge fund strategies, approximately 57% are equity related, 37% pursue a multi-strategy approach and 6% are focused on distressed investments at December 31, 2014.For a discussion of the fair value levels and the valuation methodologies used to measure fixed maturity securities, equities, derivatives and short term investments, see Note D to the Consolidated Financial Statements.The tables below present a reconciliation for all pension plan assets measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the years ended December 31, 2014 and 2013.Level 3(In millions)Balance at January 1, 2014 Actual return on assets still held at December 31, 2014 Actual return on assets sold during the year ended December 31, 2014 Purchases, sales and settlements Net transfers into (out of) Level 3 Balance at December 31, 2014Fixed maturity securities:           Corporate and other bonds$15 $— $— $— $— $15Equity securities8 — — (8) — —Limited partnerships:           Hedge funds322 19 — (38) — 303Private equity114 19 — (20) — 113Total limited partnerships436 38 — (58) — 416Total$459 $38 $— $(66) $— $431Level 3(In millions)Balance at January 1, 2013 Actual return on assets still held at December 31, 2013 Actual return on assets sold during the year ended December 31, 2013 Purchases, sales and settlements Net transfers into (out of) Level 3 Balance at December 31, 2013Fixed maturity securities:           Corporate and other bonds$11 $(1) $— $5 $— $15Equity securities5 3 — — — 8Limited partnerships:           Hedge funds359 56 — (77) (16) 322Private equity62 — — 52 — 114Total limited partnerships421 56 — (25) (16) 436Investment contracts with insurance company10 — — (10) — —Total$447 $58 $— $(30) $(16) $459The table below presents the estimated future minimum benefit payments to participants at December 31, 2014.Estimated Future Minimum Benefit Payments to Participants(In millions)Pension Benefits Postretirement Benefits2015$179 $52016181 42017180 42018184 42019185 32020-2024936 9In 2015, CNA expects to contribute $14 million to its pension plans and $5 million to its postretirement health care benefit plans.Savings PlansCNA sponsors savings plans, which are generally contributory plans that allow most employees to contribute a maximum of 50% of their eligible compensation, subject to certain limitations prescribed by the IRS.  The Company contributes matching amounts to participants, amounting to 70% of the first 6% (35% of the first 6% in the first year of employment) of eligible compensation contributed by the employee.  Employees vest in these contributions ratably over five years. As noted above, during 2000, employees were required to make a choice regarding their continued participation in the CNA Retirement Plan.  Employees who elected to forgo earning additional benefits in the CNA Retirement Plan and all employees hired on or after January 1, 2000 receive a Company contribution of 3% or 5% of their eligible compensation, depending on their age.  In addition, these employees are eligible to receive additional discretionary contributions of up to 2% of eligible compensation and an additional Company match of up to 80% of the first 6% of eligible compensation contributed by the employee.  These additional contributions are made at the discretion of management and are contributed to participant accounts in the first quarter of the year following management's determination of the discretionary amounts.  Employees vest in these contributions ratably over five years. Benefit expense for the Company's savings plans was $69 million, $71 million and $70 million for the years ended December 31, 2014, 2013 and 2012. |

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| - Definition
The entire disclosure for pension and other postretirement benefits.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414718&loc=d3e28014-114942Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e2410-114920Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 80 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=35742057&loc=SL14450702-114947Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6414199&loc=d3e39622-114963Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39675-114964
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