The Federal Reserve on Thursday released scores for 18 U.S. bank holding companies that show how low their capital ratios would fall under proposed plans for dividends and stock buybacks if "severely adverse" economic conditions unfolded over the next two years.

The Fed rejected plans by BB&T Corp and Ally Financial to return capital to shareholders, and granted Goldman Sachs and JPMorgan & Chase conditional approval, saying they had to improve the processes they use to determine their capital payouts.

American Express and Ally Financial adjusted plans submitted in January to conserve capital after getting preliminary assessments from the Fed last week. The Fed ultimately approved American Express's capital plan.

(Reporting by Sam Forgione in New York; Editing by Andrea Ricci)