Stocks Open Lower as Oil Prices, 3M Weigh  NEW YORK (Reuters) - U.S. stocks opened lower on Monday as  oil prices held near \$55 a barrel and Dow component 3M Co.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MMM.N target=/stocks/quickinfo/fullquote"&gt;MMM.N&lt;/A&gt; posted results slightly below Wall Street estimates.