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; Chairman  and Chief Executive Jeffrey Greenberg resigned on Monday, 11  days after New York Attorney General Eliot Spitzer accused the  world's biggest insurance broker of rigging bids.