Loss reserves - Narrative (Details) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Mar. 31, 2026 |
Mar. 31, 2025 |
|
| Scenario 2 | ||
| Liability for Claims and Claims Adjustment Expense [Line Items] | ||
| Adjustments on prior accident year reserves | $ 47 | |
| Scenario 1 | ||
| Liability for Claims and Claims Adjustment Expense [Line Items] | ||
| Losses and LAE incurred | $ 79 | $ 78 |
| Scenario Two | ||
| Liability for Claims and Claims Adjustment Expense [Line Items] | ||
| Adjustments on prior accident year reserves | $ 39 | |