I want to hide a div which is inside a iframe , is there any way to hide a div by its attributes

example: i have a iframe i need to hide the div id="content" content in php.net

<iframe src="http://php.net/" id = 'iframe'>
      <div id="content">...</div>
</iframe>

Dont know where i am doing mistake, please help me to resolve this issue

function hideIt(){
   document.getElementById('iframe').contentWindow.document.getElementById('content').style.display = 'none';
}