Citigroup's CEO is stepping down, ending his tumultuous five-year reign as leader of the third largest bank in the United States.

The surprise announcement by Vikram Pandit sent the company's shares down 2% this morning, no doubt, as shareholders wondered what the move meant for Citigroup.

Citigroup's President and COO John Havens also resigned.

For more on the shake-up, head over to CNNMoney.com.