2/3 or 66% is very common in group policies. It should be in your group booklet but you can request a copy of the master contract so you are aware of all the provisions. You would make the request to your Insurer and Employer–by email or fax-proof of request.
Insurers love to speak in legalize or terms like commensurate earnings–it just means a wage less than you have now by a percentage. Your insurer says if you can make 66.7% of your wages that is suitable to your skills and such–then you will not meet the test for disability at the two year mark.