Legal Proceedings and Guarantees	9 Months Ended
Sep. 30, 2017
Legal Proceedings, Commitments and Contingencies, and Guarantees [Abstract]
Legal Proceedings and Guarantees	Legal Proceedings and Guarantees CNA 401(k) Plus Plan Litigation In September 2016, a class action lawsuit was filed against CCC, Continental Assurance Company (CAC) (a former subsidiary of CCC), CNAF, the Investment Committee of the CNA 401(k) Plus Plan (Plan), The Northern Trust Company and John Does 1-10 (collectively Defendants) related to the Plan. The complaint alleges that Defendants breached fiduciary duties to the Plan and caused prohibited transactions in violation of the Employee Retirement Income Security Act of 1974 when the Plan's Fixed Income Fund’s annuity contract with CAC was canceled. The plaintiff alleges he and a proposed class of Plan participants who had invested in the Fixed Income Fund suffered lower returns in their Plan investments as a consequence of these alleged violations and seeks relief on behalf of the putative class. CCC and the other defendants are contesting the case, and no class has been certified. The Plan trustees have provided notice to their fiduciary coverage insurance carriers. Progress on the litigation has been limited as the parties are currently in mediation. Based on information currently available and our assessment of the mediation, management has recorded its best estimate of probable loss; however, it is reasonably possible that the ultimate liability may differ from that amount given the inherent uncertainty involved in this matter. After consideration of available insurance coverage, management does not believe that the ultimate resolution of this matter will have a material impact on the Company’s results of operations or financial position though the timing of recognition of any additional loss, if any, and insurance recovery, if any, may differ. Small Business Premium Rate Adjustment In prior quarters, the Company identified rating errors related to its multi-peril package product and workers' compensation policies within its Small Business unit, and the Company determined that it would voluntarily issue premium refunds along with interest on affected policies. After the rating errors were identified, written and earned premium have been reported net of any impact from the premium rate adjustments. There was no premium development impact for the three months ended September 30, 2017 and $37 million of adverse premium development was recognized as a result of the rating errors for the nine months ended September 30, 2017. Pretax operating income was reduced by $1 million and $7 million for the three and nine months ended September 30, 2017 for interest due to policyholders on the premium rate adjustments. The policyholder refunds for the multi-package product were issued in the current quarter. The estimated refund liability for the workers' compensation policies as of September 30, 2017 was $61 million including interest. Any fines or penalties related to the foregoing are reasonably possible, but are not expected to be material to the Company's results of operations or financial position. Other Litigation The Company is a party to other routine litigation incidental to its business, which, based on the facts and circumstances currently known, is not material to the Company's results of operations or financial position. Guarantees As of September 30, 2017 and December 31, 2016, the Company had recorded liabilities of approximately $5 million related to guarantee and indemnification agreements. Management believes that it is not likely that any future indemnity claims will be significantly greater than the amounts recorded. In the course of selling business entities and assets to third parties, the Company agreed to guarantee the performance of certain obligations of previously owned subsidiaries and to indemnify purchasers for losses arising out of breaches of representations and warranties with respect to the business entities or assets sold, including, in certain cases, losses arising from undisclosed liabilities or certain named litigation. Such guarantee and indemnification agreements in effect for sales of business entities, assets and third-party loans may include provisions that survive indefinitely. As of September 30, 2017, the aggregate amount related to quantifiable guarantees was $375 million and the aggregate amount related to quantifiable indemnification agreements was $254 million. In certain cases, should the Company be required to make payments under any such guarantee, it would have the right to seek reimbursement from an affiliate of a previously owned subsidiary. In addition, the Company has agreed to provide indemnification to third-party purchasers for certain losses associated with sold business entities or assets that are not limited by a contractual monetary amount. As of September 30, 2017, the Company had outstanding unlimited indemnifications in connection with the sales of certain of its business entities or assets that included tax liabilities arising prior to a purchaser's ownership of an entity or asset, defects in title at the time of sale, employee claims arising prior to closing and in some cases losses arising from certain litigation and undisclosed liabilities. Certain provisions of the indemnification agreements survive indefinitely, while others survive until the applicable statutes of limitation expire, or until the agreed-upon contract terms expire. The Company also provided guarantees, if the primary obligor fails to perform, to holders of structured settlement annuities provided by a previously owned subsidiary. As of September 30, 2017, the potential amount of future payments the Company could be required to pay under these guarantees was approximately $1.8 billion, which will be paid over the lifetime of the annuitants. The Company does not believe any payment is likely under these guarantees, as the Company is the beneficiary of a trust that must be maintained at a level that approximates the discounted reserves for these annuities.

Legal Proceedings and Guarantees

CNA 401(k) Plus Plan Litigation

In September 2016, a class action lawsuit was filed against CCC, Continental Assurance Company (CAC) (a former subsidiary of CCC), CNAF, the Investment Committee of the CNA 401(k) Plus Plan (Plan), The Northern Trust Company and John Does 1-10 (collectively Defendants) related to the Plan. The complaint alleges that Defendants breached fiduciary duties to the Plan and caused prohibited transactions in violation of the Employee Retirement Income Security Act of 1974 when the Plan's Fixed Income Fund’s annuity contract with CAC was canceled. The plaintiff alleges he and a proposed class of Plan participants who had invested in the Fixed Income Fund suffered lower returns in their Plan investments as a consequence of these alleged violations and seeks relief on behalf of the putative class. CCC and the other defendants are contesting the case, and no class has been certified. The Plan trustees have provided notice to their fiduciary coverage insurance carriers. Progress on the litigation has been limited as the parties are currently in mediation.

Based on information currently available and our assessment of the mediation, management has recorded its best estimate of probable loss; however, it is reasonably possible that the ultimate liability may differ from that amount given the inherent uncertainty involved in this matter. After consideration of available insurance coverage, management does not believe that the ultimate resolution of this matter will have a material impact on the Company’s results of operations or financial position though the timing of recognition of any additional loss, if any, and insurance recovery, if any, may differ.

Small Business Premium Rate Adjustment

In prior quarters, the Company identified rating errors related to its multi-peril package product and workers' compensation policies within its Small Business unit, and the Company determined that it would voluntarily issue premium refunds along with interest on affected policies. After the rating errors were identified, written and earned premium have been reported net of any impact from the premium rate adjustments. There was no premium development impact for the three months ended September 30, 2017 and $37 million of adverse premium development was recognized as a result of the rating errors for the nine months ended September 30, 2017. Pretax operating income was reduced by $1 million and $7 million for the three and nine months ended September 30, 2017 for interest due to policyholders on the premium rate adjustments.

The policyholder refunds for the multi-package product were issued in the current quarter. The estimated refund liability for the workers' compensation policies as of September 30, 2017 was $61 million including interest. Any fines or penalties related to the foregoing are reasonably possible, but are not expected to be material to the Company's results of operations or financial position.

Other Litigation

The Company is a party to other routine litigation incidental to its business, which, based on the facts and circumstances currently known, is not material to the Company's results of operations or financial position.

Guarantees

As of September 30, 2017 and December 31, 2016, the Company had recorded liabilities of approximately $5 million related to guarantee and indemnification agreements. Management believes that it is not likely that any future indemnity claims will be significantly greater than the amounts recorded.

In the course of selling business entities and assets to third parties, the Company agreed to guarantee the performance of certain obligations of previously owned subsidiaries and to indemnify purchasers for losses arising out of breaches of representations and warranties with respect to the business entities or assets sold, including, in certain cases, losses arising from undisclosed liabilities or certain named litigation. Such guarantee and indemnification agreements in effect for sales of business entities, assets and third-party loans may include provisions that survive indefinitely. As of September 30, 2017, the aggregate amount related to quantifiable guarantees was $375 million and the aggregate amount related to quantifiable indemnification agreements was $254 million. In certain cases, should the Company be required to make payments under any such guarantee, it would have the right to seek reimbursement from an affiliate of a previously owned subsidiary.

In addition, the Company has agreed to provide indemnification to third-party purchasers for certain losses associated with sold business entities or assets that are not limited by a contractual monetary amount. As of September 30, 2017, the Company had outstanding unlimited indemnifications in connection with the sales of certain of its business entities or assets that included tax liabilities arising prior to a purchaser's ownership of an entity or asset, defects in title at the time of sale, employee claims arising prior to closing and in some cases losses arising from certain litigation and undisclosed liabilities. Certain provisions of the indemnification agreements survive indefinitely, while others survive until the applicable statutes of limitation expire, or until the agreed-upon contract terms expire.

The Company also provided guarantees, if the primary obligor fails to perform, to holders of structured settlement annuities provided by a previously owned subsidiary. As of September 30, 2017, the potential amount of future payments the Company could be required to pay under these guarantees was approximately $1.8 billion, which will be paid over the lifetime of the annuitants. The Company does not believe any payment is likely under these guarantees, as the Company is the beneficiary of a trust that must be maintained at a level that approximates the discounted reserves for these annuities.