Fair value measurements - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Parenthetical) (Detail) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2023 |
Jun. 30, 2025 |
Dec. 31, 2024 |
|
| Fair Value, off-Balance-Sheet Risks, Disclosure Information [Line Items] | |||
| Reserve Funds | $ 53,200.0 | $ 37,500.0 | |
| Derivative Host Contracts | $ 1.6 | $ 1.2 | $ 0.8 |
| Obligation To Return Collateral Digital Assets | $ 1.9 |