Summation of sub document field based on a group unexpected

Question

I have a document structured as

{

"_id" : ObjectId("5763d4a54da83b98f269878a"),

"Company_id" : "INTG",

"First_Name" : "fgfg",

"Last_Name" : "Sharma",

"Emp_Id" : "301",

"Department" : "QA",

"Emp_Status" : "Active",

"Salary" : {

"HRA" : "1200",

"Basic" : "1000",

"Home_Allowance" : "100",

"Other_Allowance" : "400"

}

}

{

"_id" : ObjectId("5763d4b94da83b98f269878b"),

"Company_id" : "INTG",

"First_Name" : "reena",

"Last_Name" : "Sharma",

"Emp_Id" : "301",

"Department" : "QA",

"Emp_Status" : "Active",

"Salary" : {

"HRA" : "200",

"Basic" : "1000",

"Home_Allowance" : "100",

"Other_Allowance" : "100"

}

}

And i want to get sum of basic salary based on department Like

**Expected output**

**Department Total_Basic**

QA 2000

I have used the following code to get the output

db.Employee_Detail.aggregate([

{$unwind:"$Salary"}, {$group: {"_id": "$Department", total_Basic: {$sum: "$Salary.Basic" }

}}

])

But i get the below Result....

Department Total_Basic

QA 0

I think $unwind is not Working..Please suggest