Return JSON data from Web API using C# in ASP.Net MVC

I have created a web api to retrieve values from the database. The data retrieved are in the form of xml but I want it as json data.

CustomerDetailsController.cs : 

using WebApiDemo.Models;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;

namespace WebApiDemo.Controllers
{
    public class CustomerDetailsController : ApiController
    {
        public static IList<CustomerDetail> listCusDt = new List<CustomerDetail>()
        {
        };

        [AcceptVerbs("GET")]
        public CustomerDetail RPCStyleMethodFetchFirstCustomerDetails()
        {
            return listCusDt.FirstOrDefault();
        }

        [HttpGet]
        [ActionName("GetAllCustomerDetails")]
        public List<CustomerDetail> Get(string id)
        {
            SqlDataReader reader = null;
            SqlConnection myConnection = new SqlConnection();
            myConnection.ConnectionString = ConfigurationManager.ConnectionStrings["ERPConnectionString"].ConnectionString;
            SqlCommand sqlCmd = new SqlCommand();
            sqlCmd.CommandType = CommandType.StoredProcedure;
            //sqlCmd.Parameters.Clear();       
            sqlCmd.CommandText = "getBasketsForCustomer";                     
            sqlCmd.Connection = myConnection;
            sqlCmd.Parameters.AddWithValue("@CustomerId", id);
            myConnection.Open();
            reader = sqlCmd.ExecuteReader();
            List<CustomerDetail> customerDetails = new List<CustomerDetail>();          
            while (reader.Read())
            {
                CustomerDetail cusdt = new CustomerDetail();
                cusdt.OrderId = Convert.ToInt32(reader.GetValue(0));
                cusdt.CustomerId = reader.GetValue(1).ToString();
                cusdt.OrderDate = reader.GetValue(2).ToString();
                cusdt.ProductName = reader.GetValue(3).ToString();
                cusdt.Quantity = Convert.ToInt32(reader.GetValue(4));
                cusdt.UnitPrice = Convert.ToInt32(reader.GetValue(5));
                cusdt.Amount = Convert.ToInt32(reader.GetValue(6));
                customerDetails.Add(cusdt);
            }            
            return customerDetails;
            myConnection.Close();
        }
    }
}

CustomerDetail.cs :

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace WebApiDemo.Models
{
    public class Customer
    {
        public string CustomerId { get; set; }
        public string CompanyName { get; set; }
        public string City { get; set; }
    }
}