I'm studying AWS api to retrieve requisite information about my EC2 instances. 

So, I'm on AWS Cost Explorer Service.

It has function 'GetCostAndUsage' that, for example, sends information below. (this is an example from official AWS document)

```
{
"TimePeriod": {
"Start":"2017-09-01",
"End": "2017-10-01"
},
"Granularity": "MONTHLY",
"Filter": {      
"Dimensions": {
  "Key": "SERVICE",
  "Values": [
    "Amazon Simple Storage Service"
  ]
}
},
"GroupBy":[
{
  "Type":"DIMENSION",
  "Key":"SERVICE"
},
{
  "Type":"TAG",
  "Key":"Environment"
}
],
 "Metrics":["BlendedCost", "UnblendedCost", "UsageQuantity"]
}

```

and retrieve information below. (this is an example from official AWS document) 

```
{
"GroupDefinitions": [
{
  "Key": "SERVICE",
  "Type": "DIMENSION"
},
{
  "Key": "Environment",
  "Type": "TAG"
}
],
"ResultsByTime": [
{
  "Estimated": false,
  "Groups": [
    {
      "Keys": [
        "Amazon Simple Storage Service",
        "Environment$Prod"
      ],
      "Metrics": {
        "BlendedCost": {
          "Amount": "39.1603300457",
          "Unit": "USD"
        },
        "UnblendedCost": {
          "Amount": "39.1603300457",
          "Unit": "USD"
        },
        "UsageQuantity": {
          "Amount": "173842.5440074444",
          "Unit": "N/A"
        }
      }
    },
    {
      "Keys": [
        "Amazon Simple Storage Service",
        "Environment$Test"
      ],
      "Metrics": {
        "BlendedCost": {
          "Amount": "0.1337464807",
          "Unit": "USD"
        },
        "UnblendedCost": {
         "Amount": "0.1337464807",
          "Unit": "USD"
        },
        "UsageQuantity": {
          "Amount": "15992.0786663399",
          "Unit": "N/A"
        }
      }
    }
  ],
  "TimePeriod": {
    "End": "2017-10-01",
    "Start": "2017-09-01"
  },
  "Total": {}
}
]
}

```

The retrieved data in key 'Metrics' I guess, it is total cost. not each. 
So, How can I get each usage and cost for each EC2 instance??