Storing Actual Data in Multiple Currencies
Prerequisites
Before you can update data in CO-PA in two currencies, you need to activate the company code currency on the Attributes screen for your operating concern. You do this in Customizing under Structures
® Operating Concern ® Maintain Operating Concern. 
You can activate the company code currency when you first activate your operating concern, or you can activate it later for all subsequent postings.
Use
When actual data is posted in CO-PA, the system technically creates two line items: one in the operating concern currency and one in the company code currency.
Where possible, the values in each currency are taken directly from the original documents (invoices, G/L accounts, and so on). If the amounts do not exist there in the desired currency, the system translates them from the transaction currency using the exchange rate valid on the posting date. By default, CO-PA uses exchange rate type "M" (mean rate) for translating actual data. You can use other exchange rate types, though, by defining customer exits. (For more information, see the documentation on customer enhancement "COPA0004" (foreign currency translation).)
See also:
Storing Multiple Currencies in CO-PA.