COLLATERALIZED REINSURANCE, TRUST AGREEMENTS AND OTHER RESTRICTED ASSETS - Schedule of Premiums and Losses Ceded (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Mt Logan Re
Effects of Reinsurance [Line Items]
Ceded written premiums	$ 118	$ 115	$ 329	$ 365
Ceded earned premiums	118	113	329	330
Ceded losses and LAE	21	13	63	135
Assumed written premiums	1	4	3	9
Assumed earned premiums	1	4	3	9
Assumed losses and LAE	0	0	0	0
Annapurna
Effects of Reinsurance [Line Items]
Ceded written premiums	204	0	478	0
Ceded earned premiums	103	0	185	0
Ceded losses and LAE	$ 72	$ 0	$ 130	$ 0

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.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479838/944-20-50-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-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

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479032/944-605-50-1

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-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

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-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

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479032/944-605-50-1

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479032/944-605-50-1

Reference 8: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479032/944-605-50-1

Reference 9: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479032/944-605-50-1

Reference 10: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479032/944-605-50-1

Reference 11: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 944
-SubTopic 605
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479032/944-605-50-1

+ Details