CL65 CREW RECEIVED A TCASII RA DURING DSCNT INTO DTW.

Narrative

DURING OUR ARR INTO DTW WE WERE VECTORED AND SPD RESTR SEVERAL TIMES BY ZOB. WE WERE THEN GIVEN A DSCNT. AS WE WERE DSNDING; ATC GAVE US A TA FOR A NEARBY ACFT. WE REDUCED THE RANGE ON TCASII TO LOOK CLOSER AND WE NOTICED AN ACFT AT ABOUT OUR 2 O'CLOCK POS AT AN ALT BELOW OUR CURRENT ALT; BUT AT OR ABOVE OUR CLRNC ALT. THIS ACFT WAS PASSING FROM R TO L DIRECTLY IN FRONT OF OUR FLT PATH. THE CAPT TRIED TO QUERY ATC SEVERAL TIMES; BUT THE FREQ WAS VERY BUSY. ATC THEN GAVE US ANOTHER VERY CASUAL TA OF THE OTHER ACFT'S LOCATION AND ALT. REALIZING THIS WAS NOT GOING TO WORK; I BEGAN AN AGGRESSIVE LEVELOFF TO AVOID A POTENTIAL COLLISION AS OUR DSCNT WOULD HAVE TAKEN US THROUGH THE INTRUDING ACFT'S ALT AT APPROX THE SAME POS. AT THE SAME TIME; TCASII ISSUED A TA; FOLLOWED VERY SHORTLY BY AN RA INSTRUCTING US TO CLB. I DISCONNECTED THE AUTOPLT AND BEGAN AN AGGRESSIVE CLB. ATC GAVE US ANOTHER CASUAL TA AND WE RESPONDED WE WERE CLBING. I LEVELED THE ACFT AFTER TCASII RPTED 'CLR OF CONFLICT.' THEN WE BEGAN OUR DSCNT TO OUR ORIGINAL CLRED ALT ONCE AGAIN.