| **Related Party Transactions**            | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
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| **Related Party Transactions [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| Related Party Transactions                | Related Party TransactionsThe Company reimburses Loews for, or pays directly, fees and expenses of investment facilities and services provided to the Company.  Additionally, the Company provides investment-related processing services to Loews and charges Loews for these services.  The net amounts incurred by the Company for these fees, expenses and services were $60 million, $55 million and $51 million for the years ended December 31, 2024, 2023 and 2022.  Net amounts due to Loews related to these services, included in Other liabilities and payable in the first quarter of the subsequent year, were $30 million and $28 million as of December 31, 2024 and 2023.  In addition, the Company reimbursed Loews for general corporate services and related travel expenses of $1 million for the years ended December 31, 2024 and 2023.  The CNA Tax Group is included in the consolidated federal income tax return of Loews and its eligible subsidiaries.  The related payable due to Loews, included in Other liabilities, was $17 million for the year ended December 31, 2024.  The related receivable from Loews, included in Other assets, was $23 million for the year ended December 31, 2023.  For a detailed description of the income tax agreement with Loews see Note D to the Consolidated Financial Statements. In 2024, the Company invested in a commercial mortgage-backed securitization whose underlying mortgage loan is an obligation of an affiliate of Loews that matures in September of 2034.  The Company purchased $50 million of par at issuance across three separate investment grade tranches of the $305 million securitization.  The Company's position in this commercial mortgage-backed securitization is included in the Fixed maturity securities at fair value line on the Consolidated Balance Sheets and was $50 million as of December 31, 2024.  The Company recognized $1 million of income in Net investment income related to this investment during the year ended December 31, 2024.In 2021, the Company wrote an appeal bond for Loews at standard rates, which was increased in 2022, resulting in additional premium from Loews.  The aforementioned appeal bond expired in December 2022.  In addition, the Company writes, at standard rates, a limited amount of insurance for Loews and its subsidiaries.  The earned premiums for each of the years ended December 31, 2024, 2023 and 2022 were $2 million, $2 million, and $3 million. |

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| - Definition
The entire disclosure for related party transactions. 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
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