CREDIT FACILITIES - Schedule of Outstanding Letters of Credit and Borrowings (Details)	Sep. 30, 2026 USD ($)	Sep. 30, 2026 GBP (£)	Sep. 30, 2026 EUR (€)	Dec. 31, 2025 USD ($)	Dec. 31, 2025 GBP (£)	Dec. 31, 2025 EUR (€)	Oct. 26, 2025 GBP (£)	Aug. 18, 2025 USD ($)	Oct. 30, 2024 GBP (£)	Jun. 10, 2024 USD ($)	Dec. 27, 2023 USD ($)	Dec. 30, 2022 USD ($)	Nov. 21, 2022 USD ($)	Nov. 03, 2021 USD ($)	Aug. 27, 2021 USD ($)	Aug. 09, 2021 USD ($)
Line of Credit Facility [Line Items]
Commitment	$ 1,600,000,000
Total Wells Fargo Bank Bilateral LOC Facility
Line of Credit Facility [Line Items]
Commitment	350,000,000			$ 350,000,000
In Use	226,000,000			280,000,000
Wells Fargo Bank Bilateral LOC Facility - secured tranche
Line of Credit Facility [Line Items]
Commitment	175,000,000			175,000,000						$ 500,000,000
In Use	113,000,000			141,000,000
Wells Fargo Bank Bilateral LOC Facility - unsecured tranche
Line of Credit Facility [Line Items]
Commitment	175,000,000			175,000,000
In Use	113,000,000			140,000,000
Citibank LOC Facility
Line of Credit Facility [Line Items]
Commitment	370,000,000			370,000,000
In Use	227,000,000			253,000,000
Bermuda Re Citibank LOC Facility One
Line of Credit Facility [Line Items]
Commitment	230,000,000			230,000,000												$ 230,000,000
In Use	0			0
Bermuda Re Citibank LOC Facility Two
Line of Credit Facility [Line Items]
In Use	154,000,000			4,000,000
Bermuda Re Citibank LOC Facility Three
Line of Credit Facility [Line Items]
In Use	3,000,000			2,000,000
Bermuda Re Citibank LOC Facility Four
Line of Credit Facility [Line Items]
In Use	1,000,000			1,000,000
Bermuda Re Citibank LOC Facility Five
Line of Credit Facility [Line Items]
In Use	0			0
Bermuda Re Citibank LOC Facility Six
Line of Credit Facility [Line Items]
In Use	4,000,000			191,000,000
Bermuda Re Citibank LOC Facility Seven
Line of Credit Facility [Line Items]
In Use	2,000,000			1,000,000
Bermuda Re Citibank LOC Facility Eight
Line of Credit Facility [Line Items]
In Use	1,000,000			3,000,000
Bermuda Re Citibank LOC Facility Nine
Line of Credit Facility [Line Items]
In Use	3,000,000
Bermuda Re Citibank LOC Facility Ten
Line of Credit Facility [Line Items]
In Use	1,000,000
Bermuda Re Citibank LOC Facility Eleven
Line of Credit Facility [Line Items]
In Use	0
Bermuda Re Citibank LOC Facility Twelve
Line of Credit Facility [Line Items]
In Use	0
Bermuda Re Citibank LOC Facility Thirteen
Line of Credit Facility [Line Items]
In Use	4,000,000
Bermuda Re Citibank LOC Facility Fourteen
Line of Credit Facility [Line Items]
In Use	0
Bermuda Re Citibank LOC Facility - Uncommitted Facility One
Line of Credit Facility [Line Items]
Commitment	140,000,000			140,000,000
In Use	47,000,000			1,000,000
Bermuda Re Citibank LOC Facility - Uncommitted Facility Two
Line of Credit Facility [Line Items]
In Use	8,000,000			0
Bermuda Re Citibank LOC Facility - Uncommitted Facility Three
Line of Credit Facility [Line Items]
In Use				42,000,000
Bermuda Re Citibank LOC Facility - Uncommitted Facility Four
Line of Credit Facility [Line Items]
In Use				7,000,000
Bayerische Landesbank Bilateral Secured Credit Facility - Committed
Line of Credit Facility [Line Items]
Commitment	200,000,000			200,000,000											$ 200,000,000
In Use	130,000,000			123,000,000
Total Bayerische Landesbank Bilateral Unsecured Credit Facility - Committed
Line of Credit Facility [Line Items]
Commitment	150,000,000			150,000,000
In Use	150,000,000			150,000,000
Bayerische Landesbank Bilateral Unsecured Credit Facility - Committed
Line of Credit Facility [Line Items]
Commitment	150,000,000			150,000,000								$ 150,000,000
In Use	85,000,000			150,000,000
Bermuda Re Bayerische Landesbank Bilateral Unsecured Letter Of Credit Facility Two
Line of Credit Facility [Line Items]
In Use	65,000,000
Total Lloyd's Bank LOC Facility
Line of Credit Facility [Line Items]
Commitment	250,000,000			250,000,000
In Use	249,000,000			235,000,000
Lloyd's Bank Credit Facility - Committed
Line of Credit Facility [Line Items]
Commitment	250,000,000			250,000,000				$ 250,000,000			$ 15,000,000
In Use	184,000,000			67,000,000
Bermuda Re Lloyd’s Bank Letter of Credit Facility - Committed Two
Line of Credit Facility [Line Items]
In Use	50,000,000			61,000,000
Bermuda Re Lloyd’s Bank Letter of Credit Facility - Committed Three
Line of Credit Facility [Line Items]
In Use	15,000,000			107,000,000
Barclays Bilateral Letter of Credit Facility
Line of Credit Facility [Line Items]
Commitment	200,000,000			200,000,000										$ 200,000,000
In Use	117,000,000			17,000,000
Bermuda Re Barclays Credit Facility One
Line of Credit Facility [Line Items]
Commitment	200,000,000			200,000,000
In Use	13,000,000			13,000,000
Bermuda Re Barclays Credit Facility Two
Line of Credit Facility [Line Items]
In Use	5,000,000			5,000,000
Bermuda Re Barclays Credit Facility Three
Line of Credit Facility [Line Items]
In Use	100,000,000
Total Nordea Bank ABP, NY LOC Facility
Line of Credit Facility [Line Items]
Commitment	300,000,000			300,000,000									$ 300,000,000
In Use	300,000,000			300,000,000
Nordea Bank Letter of Credit Facility - Committed
Line of Credit Facility [Line Items]
Commitment	200,000,000			200,000,000									200,000,000
In Use	200,000,000			200,000,000
Nordea Bank Letter of Credit Facility - Uncommitted
Line of Credit Facility [Line Items]
Commitment	100,000,000			100,000,000									$ 100,000,000
In Use	100,000,000			$ 100,000,000
Funds at Lloyds Syndicated Letter of Credit Facility
Line of Credit Facility [Line Items]
Commitment \| £		£ 150,000,000			£ 150,000,000		£ 150,000,000		£ 150,000,000
In Use \| £		£ 143,000,000			£ 143,000,000
Everest Reinsurance Company (Ireland), Dac Commerzbank Letter of Credit Facility One
Line of Credit Facility [Line Items]
Commitment \| €			€ 75,000,000			€ 75,000,000
In Use \| €			€ 46,000,000			51,000,000
Everest Reinsurance Company (Ireland), Dac Commerzbank Letter of Credit Facility Two
Line of Credit Facility [Line Items]
In Use	1,000,000					25,000,000
Everest Reinsurance Company (Ireland), Dac Commerzbank Letter of Credit Facility Three
Line of Credit Facility [Line Items]
In Use	0					€ 0
Everest Reinsurance Company (Ireland), Dac Commerzbank Letter of Credit Facility Four
Line of Credit Facility [Line Items]
In Use	$ 23,000,000