If you wan to change balloon text and look and feel in amchart as shown in below image , just use below code.
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graph.balloonText = "Month Description = [[value1]] \n Segment = [[value2]] \n % Terms = [[value3]]%";
// BALLOON
var balloon = chart.balloon;
// set properties
balloon.adjustBorderColor = true;
balloon.color = "#000000";
balloon.cornerRadius = 5;
balloon.borderAlpha = 0;
balloon.fillColor = "#EEEFFF";
balloon.textAlign = "left";
graph.balloonText = "Month Description = [[value1]] \n Segment = [[value2]] \n % Terms = [[value3]]%";
// BALLOON
var balloon = chart.balloon;
// set properties
balloon.adjustBorderColor = true;
balloon.color = "#000000";
balloon.cornerRadius = 5;
balloon.borderAlpha = 0;
balloon.fillColor = "#EEEFFF";
balloon.textAlign = "left";