Chicago is an American rock band formed in 1967 in Chicago, Illinois, calling themselves the Chicago Transit Authority in 1968 before shortening the name in 1969. The self-described “rock and roll band with horns” blended elements of classical music, jazz, R&B, and pop music. They began writing songs with politically charged lyrics, and later moved to a softer sound, generating several hit ballads. The group had a steady stream of hits throughout the 1970s and 1980s. In September 2008, Billboard ranked Chicago at number thirteen in a list of the top 100 artists of all time for Hot 100 singles chart success, and ranked them at number fifteen on the same list produced in October 2015. Billboard also ranked Chicago ninth on the list of the hundred greatest artists of all time in terms of Billboard 200 album chart success in October 2015. Chicago is one of the longest-running and most successful rock groups, and one of the world's best-selling groups of all time, having sold more than 100 million records. In 1971, Chicago was the first rock act to sell out Carnegie Hall for a week.