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v3.23.3

Condensed Consolidated Statements of Operations (Unaudited) - (Parenthetical) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022
Income Statement [Abstract] |  |  |  |
Insurance claims and policyholders benefits, including policyholders' dividends, remeasurement impact | $ (41) | $ (211) | $ (75) | $ (205)

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- Definition Insurance Claims And Policyholders Benefits, Including Policyholders' Dividends, Remeasurement Impact + References No definition available. + Details
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Namespace Prefix: | cna_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_IncomeStatementAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration