[{"_id":"5ebb1b2372ea8c57e6ca3681","detalle":[{"_id":"5ebb1b2372ea8c57e6ca3682","precio":2000,"kilos":2},{"_id":"5eb5c1042728d85b87014c49","precio":1500,"kilos":12}],"proveedorid":"5eb5c1042728d85b87014c49",}]

db.collection.aggregate([{"$unwind":"$detalle"},{"$set":{"total":{"$multiply":["$detalle.kilos","$detalle.precio"]}}},{"$group":{"_id":"$proveedorid","total":{"$sum":"$total"}}}])