YAHOO: The stock market posted a large loss on Tuesday as several companies posted quarterly earnings misses and cautious outlooks that overshadowed signs of improvement in the credit markets. In addition, investors digested news the U.S. government plans to take additional steps to shore up money market mutual funds.

The S&P 500 spent the entirety of the session in negative territory, although it did see large swings. The Index traded near the unchanged mark with an hour of trade left, but a surge of selling interest sent it to session lows to settle with a loss of 3.1%.

It was extremely busy session on the earnings front. Results were mixed -- of the 77 companies that reported earnings after yesterday's close and before this session's open, 52% topped estimates, 35% missed and 13% were in-line. Outlooks were cautious -- of the 49 companies that issued guidance, 45% were negative, 30% were in-line, 21% were mixed and only 3% were positive.

Some notable names that topped third quarter earnings estimates include 3M (MMM 60.02, +2.51), American Express (AXP 26.33, +1.98), DuPont (DD 33.32, -2.85), Pfizer (PFE 17.35, +0.01) and Lockheed Martin (LMT 84.43, -8.79). DuPont and Lockheed, however, issued downside earnings guidance for their fourth quarter and full year.

The more widely held companies that missed estimates include BlackRock (BLK 129.24, -13.98), Caterpillar (CAT 38.84, -2.06), Freeport-McMoRan (FCX 32.81, -3.91) and Texas Instruments (TXN 16.85, -1.13). Texas Instruments also gave a downside fourth quarter earnings outlook, citing a slowdown in orders.

With regard to the government's latest effort, the Fed will buy commercial paper -- which is short-term corporate debt that many businesses rely on -- from money market mutual funds. The Fed said it created the facility because money market mutual funds and other investors have had difficulty selling assets to satisfy redemption requests and meet portfolio rebalancing needs. The Fed had already announced plans to buy commercial paper directly from companies.

While the Fed needing to shore up money market funds shows that the financial markets remain considerably strained, there continue to be signs of improvement. The rates banks charge each other for short-term dollar loans, measured by Libor, decreased across all terms.

In the end all ten sectors posted a decline in broad-based weakness.  Volume was on the light side with 1.16 billion shares exchanging hands on the NYSE, which is short of the one-year average of 1.49 billion.

The tech sector (-5.6%) posted a large decline due to the 6.3% drop in Texas Instruments. An earnings warning from Sun Microsystems (JAVA 4.78, -1.00) also weighed on the sector.

The energy sector fell 4.3% as crude prices dropped 4.5% to $70.89 per barrel.  The drop in crude prices was fueled by global economic concerns and a 1.5% surge in the dollar.

The materials sector declined 5.7% after copper producer Freeport McMoRan plunged 11%.

The financial sector outperformed on a relative basis with a loss of 1.8%. Strength in American Express helped offset weakness in BlackRock and Citigroup (C 14.17, -0.92). DJ30 -231.77 NASDAQ -73.35 SP500 -30.35 NASDAQ Adv/Vol/Dec 745/2.15 bln/2029 NYSE Adv/Vol/Dec 925/1.16 bln/2182