[{"_id":1,"data":{"status":{"COMPLETED":[{"count":1.0,"assignee":"ABC"},{"count":1.0,"assignee":"DEF"}],"OPEN":[{"count":5.0,"assignee":"XYZ"},{"count":5.0,"assignee":"PQR"}]},"assignee":{"User1":[{"count":1.0,"status":"OPEN"}],"User2":[{"count":5.0,"status":"COMPLETED"}]}}},{"_id":2,"data":{"status":{"COMPLETED":[{"count":10.0,"assignee":"AAA"},{"count":10.0,"assignee":"BBB"}],"OPEN":[{"count":50.0,"assignee":"CCC"},{"count":50.0,"assignee":"DDD"}]},"assignee":{"User1":[{"count":10.0,"status":"OPEN"}],"User2":[{"count":15.0,"status":"COMPLETED"}]}}}]

db.collection.aggregate([{$project:{obj:{$map:{input:{$objectToArray:"$data.status"},in:{k:"$$this.k",count:{$sum:"$$this.v.count"}}}}}},{$unwind:"$obj"},{$group:{_id:"$obj.k",count:{"$sum":"$obj.count"}}}])