Fannie Mae Will Keep More Cash on Hand  WASHINGTON (Reuters) - Embattled mortgage finance company  Fannie Mae &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=FNM.N target=/stocks/quickinfo/fullquote"&gt;FNM.N&lt;/A&gt; agreed to keep billions of dollars more cash  on hand while it corrects accounting problems, its government  regulator said on Monday.