In my case, i prefer not use Web.config. Then i created code above in Global.asax file:
protected void Application_Error(object sender, EventArgs e)
    {
        Exception ex = Server.GetLastError();
        //Not Found (When user digit unexisting url)
        if(ex is HttpException && ((HttpException)ex).GetHttpCode() == 404)
        {
            HttpContextWrapper contextWrapper = new HttpContextWrapper(this.Context);
            RouteData routeData = new RouteData();
            routeData.Values.Add("controller", "Error");
            routeData.Values.Add("action", "NotFound");
            IController controller = new ErrorController();
            RequestContext requestContext = new RequestContext(contextWrapper, routeData);
            controller.Execute(requestContext);
            Response.End();
        }
        else //Unhandled Errors from aplication
        {
            ErrorLogService.LogError(ex);
            HttpContextWrapper contextWrapper = new HttpContextWrapper(this.Context);
            RouteData routeData = new RouteData();
            routeData.Values.Add("controller", "Error");
            routeData.Values.Add("action", "Index");
            IController controller = new ErrorController();
            RequestContext requestContext = new RequestContext(contextWrapper, routeData);
            controller.Execute(requestContext);
            Response.End();
        }
    }
And thtat is my ErrorController.cs
public class ErrorController : Controller
{
    // GET: Error
    public ViewResult Index()
    {
        Response.StatusCode = 500;
        Exception ex = Server.GetLastError();
        return View("~/Views/Shared/SAAS/Error.cshtml", ex);
    }
    public ViewResult NotFound()
    {
        Response.StatusCode = 404;
        return View("~/Views/Shared/SAAS/NotFound.cshtml");
    }
}
And that is my ErrorLogService.cs based on mason class
//common service to be used for logging errors
public static class ErrorLogService
{
    public static void LogError(Exception ex)
    {
        //Do what you want here, save log in database, send email to police station
    }
}