You can see your CyberSource «Merchant ID» («Organization ID») for your CyberSource «Account Admin» in the «Account Admin» section of the «Merchant Registration Confirmation» letter:
It is valid only if you have configured your CyberSource «Account Admin» account.
You have specified it on the Step 3 of the of the «[CyberSource] How to configure an «Account Admin» account?» instruction: