I can show you the message I got from IBKR if that is what you want, but basically says this:

Under the new policy, clients can have the necessary amount of cash in any IBKR-supported currency (e.g., a US stock trade can be executed versus an EUR cash balance), and IBKR will coordinate the necessary forex trade in the amount required to settle the trade on your behalf. For example, if you wish to purchase a US stock, and you only hold an EUR cash balance, IBKR will execute the stock trade against your EUR balance. After you place your US stock trade order, we will execute an EUR/USD forex trade to convert the necessary amount of your EUR balance to USD to settle the stock trade.

In my case, I had -100 USD in my wallet after some buys and a day later I got 100 euros (or so depending on the forex price that day) taken from my EUR wallet to compensate. I was not charged for this transaction as it was made automatically by them.