Pathfinder belt issues

[Todd244]

I own a 2003 Pathfinder LE and I love it but about a month and a half ago I replaced both my serpentine belt and the A/C belt and things were golden. I tightened them about a week later after the belts had stretched a little bit but the squeek was gone. Last night I was driving home and I heard a loud POP and a ding ding ding as something metal tumbled down the highway all of the lights on my dash board light up and I lose power steering. When I finally limp it home and check the belt its still intact but is dangling off of the pulleys. I checked the pulleys and can't find anything that looks out of place but something definitely fell out of the car. Any idea of what could of went wrong or caused this? Any help would be greatly appreciated.

[Hawairish]

Did the idler pulley turn ok afterwards? On a different Nissan, the bearings grenaded from the idler pulley sending the individual bearings flying around my engine compartment. The idler bearings is the adjustable ones with smooth faces.