Blue Chips Fall on Commodity, Oil Stocks  NEW YORK (Reuters) - U.S. blue chips fell on Wednesday as a  steep decline in commodity prices and lower crude oil dented  shares of Alcoa Inc. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=AA.N target=/stocks/quickinfo/fullquote"&gt;AA.N&lt;/A&gt; and Exxon Mobil Corp.&lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=XOM.N target=/stocks/quickinfo/fullquote"&gt;XOM.N&lt;/A&gt;,  outweighing strong earnings from McDonald's Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=MCD.N target=/stocks/quickinfo/fullquote"&gt;MCD.N&lt;/A&gt;.