After Citigroup unexpectedly failed the Federal Reserve’s annual stress tests in March 2014, the bank opened its checkbook and called in the consultants.

The firm had to address several of the regulator's concerns in a short time frame, and no single consulting firm could do the job, according to people familiar with the matter. The bank hired multiple firms and said it spent about $180 million on stress tests during the second half of 2014. The next year, it passed.