Citi joined JPMorgan as the world's most systemically important banks, replacing HSBC in a group of 30 lenders who must hold extra capital from 2019 to preserve financial stability.
The group of 20 economies (G20) agreed after the 2007-09 financial crisis that top lenders, whose size and complexity means that a collapse could wreak havoc in markets, should hold extra capital, according to the level of risk they present.
In the annual update of rankings published on Monday by the Financial Stability Board (FSB), Citi has replaced HSBC in the top "bucket" of a 2.5 percent capital surcharge on top of the global minimum requirements.
HSBC joins Bank of America, BNP Paribas and Deutsche Bank in the next category down, with a surcharge of 2 percent.
The FSB, a G20 regulatory task force, also updated its list of 9 globally systemically important insurers, which was unchanged from last year.