XML 137 R122.htm IDEA: XBRL DOCUMENT
v3.25.0.1

Reinsurance (Components of Written Premiums) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Premiums Written, Net [Abstract] |  |  |
Direct | $ 15,509 | $ 14,902 | $ 14,264
Assumed | 298 | 262 | 281
Ceded | 5,202 | 5,272 | 5,417
Net | 10,605 | 9,892 | 9,128
Property and casualty |  |  |
Premiums Written, Net [Abstract] |  |  |
Direct | 15,120 | 14,498 | 13,843
Assumed | 257 | 219 | 235
Ceded | 5,202 | 5,272 | 5,417
Net | 10,175 | 9,445 | 8,661
Long-term care |  |  |
Premiums Written, Net [Abstract] |  |  |
Direct | 389 | 404 | 421
Assumed | 41 | 43 | 46
Ceded | 0 | 0 | 0
Net | $ 430 | $ 447 | $ 467
Percentage of assumed premiums written to net premiums written |  |  |
Premiums Written, Net [Abstract] |  |  |
Assumed/ Net % | 2.80% | 2.60% | 3.10%
Percentage of assumed premiums written to net premiums written | Property and casualty |  |  |
Premiums Written, Net [Abstract] |  |  |
Assumed/ Net % | 2.50% | 2.30% | 2.70%
Percentage of assumed premiums written to net premiums written | Long-term care |  |  |
Premiums Written, Net [Abstract] |  |  |
Assumed/ Net % | 9.50% | 9.60% | 9.90%

X
- Definition Percentage of Assumed Premium Written to Premium Written Net + References No definition available. + Details
Name: | cna_PercentageOfAssumedPremiumWrittenToPremiumWrittenNet
Namespace Prefix: | cna_
Data Type: | dtr-types1:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of written premiums assumed from other entities. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 + Details
Name: | us-gaap_AssumedPremiumsWritten
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of written premiums ceded to other entities. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(3) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 + Details
Name: | us-gaap_CededPremiumsWritten
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, before premiums ceded to other entities and premiums assumed by the entity, of premiums written. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 + Details
Name: | us-gaap_DirectPremiumsWritten
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount, after premiums ceded to other entities and premiums assumed by the entity, of premiums written. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(1) -SubTopic 605 -Topic 944 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(1) -SubTopic 605 -Topic 944 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 + Details
Name: | us-gaap_PremiumsWrittenNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Details
Name: | srt_ProductOrServiceAxis=us-gaap_PropertyLiabilityAndCasualtyInsuranceSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_ProductOrServiceAxis=cna_LongtermcareInsuranceProductLineMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | cna_PercentageofassumedpremiumswrittentonetpremiumswrittenAxis=cna_PercentageOfAssumedPremiumsWrittenToNetPremiumsWrittenMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |