STATUTORY REQUIREMENTS - Statutory Capital and Surplus (Details) - USD ($) $ in Thousands |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Bermuda | ||
| Statutory Accounting Practices [Line Items] | ||
| Statutory capital and surplus | $ 13,964,117 | $ 12,241,253 |
| Required statutory capital and surplus | 2,784,207 | 2,669,916 |
| Switzerland | ||
| Statutory Accounting Practices [Line Items] | ||
| Statutory capital and surplus | 1,640,000 | 1,606,000 |
| Required statutory capital and surplus | 987,000 | 862,000 |
| U.K. | ||
| Statutory Accounting Practices [Line Items] | ||
| Statutory capital and surplus | 911,990 | 952,309 |
| Required statutory capital and surplus | 911,990 | 952,309 |
| U.S. | ||
| Statutory Accounting Practices [Line Items] | ||
| Statutory capital and surplus | 1,301,880 | 1,260,230 |
| Required statutory capital and surplus | $ 965,475 | $ 965,631 |