Citigroup has kicked off the earnings season for big US banks in the fourth quarter, which will likely prove to have been a difficult period for Wall Street's bond traders.

Citi's figures will be closely watched as more than a bellwether for rivals that report later this week; The Wall Street Journalreported on January 11 that Citi had agreed to give the activist investor ValueAct Capital Partners a closer look at its business model. ValueAct, which holds a roughly 1.3% stake in Citi, is not currently seeking a seat on the bank's board.