| **Related Party Transactions**            | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
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| **Related Party Transactions [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Related Party Transactions                | Note Q. Related Party Transactions The Company reimburses Loews, or pays directly, for management fees, travel and related expenses, software fees, and expenses of investment facilities and services provided to the Company.  The amounts reimbursed or paid by the Company were $38 million, $38 million and $33 million for the years ended December 31, 2011, 2010 and 2009.  The CNA Tax Group is included in the consolidated federal income tax return of Loews and its eligible subsidiaries.  See Note E for a detailed description of the income tax agreement with Loews.  In addition, the Company writes, at standard rates, a limited amount of insurance for Loews and its subsidiaries.  The earned premiums for the years ended December 31, 2011, 2010 and 2009 were $2 million, $2 million and $2 million.CNA previously sponsored a stock ownership plan whereby the Company financed the purchase of Company common stock by certain former officers, including executive officers.  Interest charged on the principal amount of these outstanding stock purchase loans is generally equivalent to the long term applicable federal rate, compounded semi-annually, in effect on the disbursement date of the loan.  Loans made pursuant to the plan are generally full recourse and are secured by the stock purchased.  The loans were originally issued with a ten-year maturity date, and the majority of the remaining loans have been extended with terms maturing through October 2014. The carrying value of the loans as of December 31, 2011 approximates the fair value of the related common stock collateral. |

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| - Definition
The entire disclosure for related party transactions, including the nature of the relationship(s), a description of the transactions, the amount of the transactions, the effects of any change in the method of establishing the terms of the transaction from the previous period, stated interest rate, expiration date, terms and manner of settlement per the agreement with the related party, and amounts due to or from related parties. If the entity and one or more other entities are under common ownership or management control and this control affects the operating results or financial position, disclosure includes the nature of the control relationship even if there are no transactions between the entities. Disclosure may also include the aggregate amount of current and deferred tax expense for each statement of earnings presented where the entity is a member of a group that files a consolidated tax return, the amount of any tax related balances due to or from affiliates as of the date of each statement of financial position presented, the principal provisions of the method by which the consolidated amount of current and deferred tax expense is allocated to the members of the group and the nature and effect of any changes in that method. Examples of related party transactions include transactions between (a) a parent company and its subsidiary; (b) subsidiaries of a common parent; (c) and entity and its principal owners; and (d) affiliates.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(k)) -URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 3A -Section 04 -Paragraph bReference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 57 -Paragraph 1-4 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39678-107864Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 4 -Section 08 -Paragraph kReference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39691-107864Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39622-107864Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 850 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39603-107864
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