LOSS OF SEPARATION BTWN LNDG AND DEPARTING ACFT.

Narrative

WHILE CONDUCTING A CAT I ILS RWY 3R AT DTW; DTW TWR CLRED AN AIRBUS (Y) INTO POS ON RWY 3R AFTER A LNDG PLANE (Z). THE LNDG PLANE THAT PRECEDED US MISSED HIS TXWY TURNOFF. TWR ISSUED FURTHER INSTRUCTIONS FOR THE LNDG PLANE (Z) TO EXPEDITE. THE ACFT IN POS (Y) WAS ISSUED TKOF CLRNC WHEN WE WERE 200 FT ABOVE OUR DECISION HT. (THE 200 FT DECISION HT WAS 1/2 MI FROM THRESHOLD.) OUR DECISION HT WAS 200 FT AGL AS WE WERE ON A CAT 1 MINIMUM. SO; WE WERE AT 400 FT ABOVE TOUCHDOWN ZONE WHEN THE AIRBUS (Y) GOT THE TKOF CLRNC. MISSED APCH CLRNC WAS NEVER ISSUED TO US. THIS ENTIRE APCH WAS CONDUCTED IN IMC. IN FACT; WE DID A MISSED APCH AT DECISION HT DUE TO INADEQUATE VISUAL REFS. AS IT TURNED OUT; AS WE DID OUR MISSED APCH; THE AIRBUS (Y) WAS LIFTING OFF. WE ADVISED DTW TWR THAT WE HAD MISSED APCH AND HE IMMEDIATELY ISSUED A L HEADING CHANGE TO THE AIRBUS (Y) AND A R HEADING CHANGE TO US (X). AT ONE POINT ON THE BUSY MISSED APCH; I NOTICED THAT THE TCASII TFC SYMBOL OF THE PLANE (Y) WAS EXACTLY UNDER OUR PLANE ONLY 300 FT AND CLBING OUT WITH US. WE TURNED R AND PROCEEDED TO THE ALTERNATE (CLE) FOR FUEL. AFTER LNDG; OUR DISPATCH AND ATC SPECIALIST WERE NOTIFIED OF THIS SIT AND OUR ATC SPECIALIST CALLED DTW TWR AND THEY CONFIRMED THE SAME STORY AND THE 300 FT SEPARATION. IN RETROSPECT; A MISSED APCH SHOULD HAVE BEEN ISSUED BY ATC. IN THE ABSENCE OF THAT; I SHOULD HAVE EXECUTED ONE EARLIER DUE TO THE TFC CONFLICT (ACFT ON THE RWY).