Markk321,
Assuming that you are referring to the ORDERS01 IDOC, there are several segments that provide identical fields to the one that you identified. However, I'm not that I am clear on what you're trying to do. Do you want to store it at the Detail or Header level?
Also, I recommend that you post IDOC-related questions to the "SAP ERP Solutions" forum. You'll probably get more responses over there.