Marsh   McLennan CEO Greenberg Resigns  NEW YORK (Reuters) - Marsh   McLennan Cos. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MMC.N target=/stocks/quickinfo/fullquote"&gt;MMC.N&lt;/A&gt; said on  Monday Chairman and Chief Executive Jeffrey Greenberg resigned,  11 days after New York's attorney general accused the world's  biggest insurance broker of rigging insurance prices.