Instead of generating a usage statement, you're able to generate a CDR file which your customer can then upload to their billing platform of choice.
To do so, first, head to the Customers screen and select the customer that requires CDRs to be generated. Next, select Edit Details and scroll down the options until you get to the Itemised Statement field and select CDR from the available options.
Within the CDR file, there is a column for what are known as charge codes which serve as a destination's identifier when importing into a billing platform. By default, the Charge Code you output will match the Charge Code of the CDR you imported in, so if your customer made a call to a destination with a Charge Code of "National", the output Charge Code would also be "National".
You can optionally decide to override this Charge Code, by going to Destinations > Voice, Data & SMS > {Destination} > CDR Output (top-right) and entering what you wish the output Charge Code for this Destination to be in CDRs you generate.
CDR Sample and Specification
For a sample of the CDR output and the specification, please see the attachments to this article.