When Intercompany Bills and Invoices are not paid/collected, these transactions are eliminated at month end when performing the Eliminate Intercompany Transactions task (under Setup > Accounting > Manage Accounting Periods). The created Elimination Journal will automatically reverse next month. This will be the process every month if these transactions are not paid/collected.
However, if Intercompany Bills and Invoices were paid/collected, these will not be included on the elimination process since the transactions were deemed closed. Any difference on the exchange rate will be posted to the Realized Gain/Loss account.