Credit Suisse Group AG's credit rating was cut three levels and Morgan Stanley's was reduced by two as Moody's Investors Service downgraded 15 banks in moves that may shake up competition among Wall Street's biggest firms.

Credit Suisse was cut to A2, the same as JPMorgan Chase & Co. and BNP Paribas SA, as Moody's completed a review of global banks with capital-markets operations it announced in February. Morgan Stanley and Zurich-based UBS AG, the other firms singled out for three-level reductions, were lowered two steps instead, the ratings firm said yesterday in a statement.

"All of the banks affected by today's actions have significant exposure to the volatility and risk of outsized losses inherent to capital-markets activities," Moody's Global Banking Managing Director Greg Bauer said in the statement.