Fair value of financial instruments - Narrative (Details) - USD ($) $ in Millions |
Mar. 31, 2026 |
Dec. 31, 2025 |
|---|---|---|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Total principal debt | $ 625 | $ 625 |
| Secured Debt | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Total principal debt | 575 | 575 |
| $575 million secured bond (Level 1) | Secured Debt | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Total principal debt | 575 | $ 575 |
| Level 1 | $575 million secured bond (Level 1) | Secured Debt | ||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Total principal debt | $ 575 |