Hewlett-Packard Co., DuPont Co. and Verizon Communications Inc. slumped 4 percent or more. Merck & Co. sank 7.7 percent, dragging down the Dow Jones Industrial Average, after agreeing to buy Schering-Plough Corp. for $41.1 billion. Aflac Inc., the largest provider of supplemental insurance, dropped 15 percent after UBS AG recommended selling the shares.
The S&P 500 fell 1 percent to 676.53, the lowest level since September 1996. The index, which decreased as much as 1.5 percent and climbed 1.7 percent, swung between gains and losses at least 25 times. The Dow average retreated 79.89 points, or 1.2 percent, to 6,547.05.
U.S. stocks last week posted the biggest decline in three months after American International Group Inc. reported a $61.7 billion loss and concern increased that General Electric Co. will be stripped of its top credit rating. General Motors Corp. sank 36 percent, the most since October, after its auditor said the automaker may not survive.