My experience may be different from others, but I have found it extremely difficult to fire someone at Citi. I happen to know of a situation where a person was almost daring me to take action for terrible performance. I put this person on a PIP, but HR wanted so much proof and evidence that I was putting in the time to help this individual succeed, I simply had to pass this person. It's not that I wouldn't put in that time, because I did, it was the fact that I had to document every single failure and explain how it equated to the individual's poor work ethic.
Keep in mind that in the current environment, when Citi is getting ready to lay off thousands of people, they can lay off someone for any reason at all. I may be forced to lay off 2/2, 2/3, etc... Heck, I may get laid off :( -
So, if you were rated poorly, and you are genuinely giving it 100%, just make sure your manager knows that you have a plan to address your his/her concerns.
In conclusion: in some teams, it is very difficult to get fired. Across the company, Citi can lay off whoever they want, whenever they want, for whatever reason they want.