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v3.22.4

Reinsurance (Voluntary Reinsurance) (Details) $ in Millions | Dec. 31, 2022 USD ($)
--- | ---
Effects of Reinsurance [Line Items] |
Total voluntary reinsurance outstanding balance | $ 4,808
A- to A++ |
Effects of Reinsurance [Line Items] |
Total voluntary reinsurance outstanding balance | 3,785
B- to B++ |
Effects of Reinsurance [Line Items] |
Total voluntary reinsurance outstanding balance | 1,020
Insolvent |
Effects of Reinsurance [Line Items] |
Total voluntary reinsurance outstanding balance | $ 3

X
- Definition Voluntary Reinsurance Recoverable, Gross + References No definition available. + Details
Name: | cna_VoluntaryReinsuranceRecoverableGross
Namespace Prefix: | cna_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_EffectsOfReinsuranceLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | cna_CreditRatingAxis=cna_AMinusToAPlusPlusMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | cna_CreditRatingAxis=cna_BMinusToBPlusPlusMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | cna_CreditRatingAxis=cna_InsolventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |