Citigroup Inc. or Citi (stylized as citi) is an American multinational investment bank and financial services corporation headquartered in New York City. 

Citigroup is ranked 3rd on the list of largest banks in the United States and, alongside JPMorgan Chase, Bank of America, and Wells Fargo, it is one of the Big Four banks of the United States.

Citigroup was formed on October 8, 1998, following the $140 billion merger of Citicorp and Travelers Group to create the world's largest financial services organization. 

Citigroup is ranked 30th on the Fortune 500 as of 2019. Citigroup has over 200 million customer accounts and does business in more than 160 countries. 

Citigroup is the holding company for the following divisions:

Citigroup Global Markets, Inc., Citigroup Global Markets Limited (UK), and Citigroup Global Markets Japan – broker dealers, including one of 24 primary dealers in United States Treasury securities. 

Citi's Institutional Clients Group (ICG) offers investment and corporate banking services and products for companies, governments, institutions, and ultra high-net-worth investors.  

According to en.wikipedia