A corps, the way the US Army operated in WWII, was an intermediate headquarters, in between an Army and the Division level.A corps didnt have any combat troops permanently attached to it, the idea being that combat divisions could be moved from corps to corps, as the mission changed.II Corps was the only corps headquarters to direct combat operations in North Africa and Sicily, and later was part of 5th Army for operations in Italy.A corps might have anywhere from two to up to five or six divisions assigned to it at any one time.A corps was usually commanded by a lieutenant general (three stars).
A corps DID have headquarters personnel permanently attached - like signallers, and also perhaps "Replacement" units, to serve as conduits for funneling replacements to where they were needed.Most divisions and many regiments published histories after the war, but Im unaware of any corps level histories... but many three stars have biographies...
It looks as though your father may have been permanently attached to the 177th Signal Replacement Company, from which "Detachment Two" was drawn, for some more or less permanent signals operation - perhaps running a message center.As the war was ending, this detachment, and the replacement company from which it was drawn, as well as possibly the entire corps headquarters, were probably being deactivated in swift and bewildering succession.... this is likely why he would have been "attached" to the unit he was discharged from - for just long enough to get him home and process the paperwork.
The awards look to be published in "General Order Number 11 of the 177th Signals Replacement Company of 1944" and "General Order Number 452 of the 7th Army of 1945".The latter one was probably for a large number of men, the former would have been just for your dad and members of his company.
I think your best bet would be to try to find, in the National Archives, operational logs and headquarters papers from the signals section of II Corps, to learn the function of his detachment.Any decent history of those campaigns will have information on II corps, but would be focused mostly on the general commanding and the combat units under his control.A memorable scene from the movie "Patton" was when Patton was sent to take over a then demoralized II corps in North Africa, and kicked the sleeping soldier in the pants.Best of luck.