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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.

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- 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

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- 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

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- 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

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- 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

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