S&P 500 index retreated from gains on Monday on renewed investor concerns about Greece's ability to meet all the requirements for receiving a bailout financing. The index slipped 0.04% or 0.57 points and closed at 1,344.33. Health insurer Humana fell 5.4% after reporting less than expected revenue and lower than predicted earnings outlook for 2012. Micron Technology lost 3% on the news company's CEO Steve Appleton died in a plane crash. Verizon Communications added 0.8% after company said it plans to launch a video-streaming service.