Ok, you'll get whatever the policy pays. Then after that, if you're permanently disabled, SS will kick in. If you didn't have any long-term disability insurance, you would get the full amount of SS to which you are entitled (based on your last 20 quarters). Since you have LTD, your SS is reduced according to a calculation you can get here:
http://www.ssa.gov/planners/calculators.htm
No SS unless you're permanently disabled according to the SS Adminstration.