Moody's grouped the 15 institutions downgraded Thursday into three categories based on their relative credit-worthiness.
In the strongest group are JPMorgan, HSBC and the Royal Bank of Canada, which Moody's said had solid capital buffers and "contained" exposure to the European crisis. Moody's also said these banks demonstrated solid risk management during the financial crisis.
In the second group are Barclays, BNP Paribas, Credit Agricole, Credit Suisse, Deutsche Bank, Goldman Sachs, Societe Generale and UBS. Moody's said these firms had varying risk factors, ranging from high dependence on capital markets operations to limited liquidity and exposure to Europe.
The weakest group includes Bank of America, Citigroup, Morgan Stanley, and Royal Bank of Scotland (RBS). Moody's said firms in this group had experienced problems with volatility and risk management, and in some cases had weaker buffers than their peers in the industry.
BofA and Citi are now rated just two notches above junk status, while Morgan Stanley sits three notches above.