CustomError Mode off not showing detailed error message in ASP.NET MVC

On localhost I have set custom error mode off in web.config. There is no Application_Error method in global.asax. I have also commented HandleErrorAttribute in filter.config, but still I am not getting detailed error message / yellow screen of err / stacktrace in my ASP.NET MVC app.

System.web section in web.config:

<system.web>
    <caching>
        <outputCache enableOutputCache="false" />            
    </caching>
    <globalization culture="auto" uiCulture="auto" />
    <customErrors  mode="Off" />
    <compilation targetFramework="4.5" debug="true" />
    <httpRuntime targetFramework="4.5" maxRequestLength="524288000" executionTimeout="3600" requestLengthDiskThreshold="524288000" maxQueryStringLength="204800" maxUrlLength="409600" enable="true" />
</system.web>

I have this line of config in system.webserver:

<system.webServer>
    <httpErrors errorMode="Detailed"/>

But when I execute simple code shown here in the HomeController's Index action method, it is redirecting to the /Home/Error page instead of showing yellow error page or detailed error page:

public ActionResult Index(string returnUrl)
{
    int b = 0;
    int a = 5 / b;

    ViewBag.Message = "Welcome BP DHC Application.";
    ViewBag.ReturnUrl = returnUrl;

    return View();
}