The Standard & Poor's 500 index fell 4.59 points, or 0.2 percent, to close at 1,973.63. Seven of the 10 industry groups fell, led by retailers and other consumer-discretionary companies.
The Dow Jones industrial average fell 48.45 points, or 0.3 percent, to 17,051.73, while the Nasdaq composite lost 7.44 points, or 0.2 percent, to 4,424.70.
European markets ended lower. Germany's DAX dropped 1.1 percent while France's CAC-40 lost 0.7 percent. Britain's FTSE 100 slipped 0.3 percent.
A few well-known companies turned in results that fell short of estimates on Monday. The toy maker Hasbro reported second-quarter earnings and revenue that came in below analysts' targets. Rising sales of My Little Pony, Transformers and other toys weren't enough to stem a decline in sales of games such as Twister. Hasbro's stock sank $1.43, or 2.7 percent, to $51.78.
Six Flags Entertainment posted higher profits and sales in the second quarter, but the theme-park operator's revenue came up short of what analysts had expected, partially a result of sluggish attendance. Six Flags slumped $1.69, or 4.1 percent, to $39.31.
Despite the dour news, the second-quarter earnings season is off to a strong start: Of the 88 companies that have reported results so far, 58 have beaten analysts' estimates.
Nearly a third of the companies in the S&P 500 index will hand in their quarterly results this week, including such heavyweights as Apple on Tuesday, Boeing on Wednesday and Amazon on Thursday.
In other trading on Monday, benchmark U.S. crude oil rose $1.46 to $104.59 a barrel on the New York Mercantile Exchange. In the market for U.S. government bonds, the yield on the 10-year Treasury note slipped to 2.47 percent from 2.48 percent late Friday.
Among other companies in the news, Yum Brands fell $3.29, or 4.3 percent, to $74.13 amid a new food-safety scare in China. The operator of KFC and Pizza Hut restaurants said its stores in China stopped buying products from a Shanghai supplier, while local officials investigate allegations that the supplier repackaged old beef and chicken and stamped new expiration dates on them.