Need Assistance

Good afternoon. I'm in the middle of my researching and writing up a narrative of my grandfather's service in the ETO. I have digital copies of his separation documents but have stumbled upon a roadblock.

Post training he was assigned to the 121 ECB (under 29 ID). Survived Normandy and Northern France, but according to the morning reports, was dropped from his company rolls in Sep '44 as a non battle casualty in the hospital. According to his separation record, he was in military police for 6 months before being transferred to Det A1A1 European Civil Affairs Division for the duration of his service (through Jan '46).

Does anyone know how I could ID and research his MP unit? The only thing I have was his own words stating that he watched/helped troops coming into the hospital during he Bulge. Would the 29 ID have had their own division hospital or were those common to multiple units? How would I find where he would have gone after he was released from his stay? The only definitive thing I know is that he did not go back to the 121 ECB.