Willis Hires Top Marsh Executive  NEW YORK (Reuters) - Insurance broker Willis Group Holdings  Ltd. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=WSH.N target=/stocks/quickinfo/fullquote"&gt;WSH.N&lt;/A&gt; on Monday said it hired a top executive from  embattled rival Marsh   McLennan Cos. Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MMC.N target=/stocks/quickinfo/fullquote"&gt;MMC.N&lt;/A&gt;