The recent turnaround in Citigroup's (C 2.82%) fortunes is great news for investors, as new management helps guide the bank to a more profitable future. Some of the bank's more lucrative sections, however, have been growing for some time, after being put in place at least two years ago. One of these is Citi's investment banking arm, the seeds of which were sown in 2010, under former CEO Vikram Pandit. The other is the bank's private bank, which services some of the wealthiest people in the world.

Family offices for the richest family firms
Around the same time as its investment banking revival, Citi created the family office sector to help the most prosperous families in the world manage their wealth. Not surprisingly, the bank set up these units in the Middle East, where some of their corporate clients developed a need for a more personal touch. Earlier this year, Citi promoted one of its own to oversee the Middle Eastern family office division.

Citi has been beefing up its Asian unit, as well. Citi won the Financial Times' Best Global Private Bank award, which noted the bank's significant Asian expansion, as well as growth in Latin America. Citigroup CEO Michael Corbat and Citi Private Bank Chief Jane Fraser recently spruced up the unit, naming a new global chief strategist after the former CIO was let go this past January. Another claim to fame: Citi Private Bank services at least one-third of the world's billionaires.

Other big banks push private banking
Private banking is part and parcel of many big banks' business model, and Bank of America (BAC 1.70%), JPMorgan Chase (JPM 1.44%), Wells Fargo (WFC -0.26%), and Goldman Sachs (GS 1.59%) all feature their own wealth units.

Though not currently on par with Citi, some are trying. Last summer, Goldman added a former Citi private banking executive to its Asian wealth management unit, and JPMorgan has been beefing up its U.K. operations, recently adding seven new faces to its ranks. Bank of America seems to be concentrating more on its U.S. operations, which CEO Brian Moynihan noted late last year was picking up steam. Last August, B of A sold its underperforming overseas units in an effort to concentrate on core businesses and boost capital.

Though both JPMorgan and Wells were "highly commended" by the Global Private Banking panel for their U.S. operations, Citi rules when it comes to managing -- and profiting from -- the wealth of the world.