Thanks, guys. FYI for those that need to remove the upper idler pulley, it's a TORX size T-50

I took a peek at my bro's c280 and I was amazed at what happened to my ML when i compared it to his- the idler pulley in the ML actually divorced itself from the bearing plus there' seems to have been a black plastic cap covering the bolt that keeps the idler pulley fastened to the carrier. That flew away too. I can't imagine how a piece as large as the outer part of the pulley assembly could not have caused one bit of damage to the radiator, fan blade, etc. when it separated from the bearing. WOW.

Anyway, when I figured it all out it was a matter of removing the looooong center bolt with the T-50 (it was torqued down very lightly fyi), pulled out the naked bearing and replaced it with a brand new idler pulley assembly ($15), lined up everything with a new belt, adjusting the spring loaded lower tensioner pulley with 17mm socket and breaker bar underneath so the belt would fit, voila....

all is right with the world again!

Thanks again guys for your replies and help!