Sullivan & Cromwell helped steer BNP Paribas SA to a historic guilty plea and settlement on Monday, bolstering the firm’s reputation as go-to counsel for banks locked in hostile negotiations with regulators. The deal could shed light on whether criminal penalties can undermine a modern bank’s viability or harm the economy at large, as some defense lawyers have argued in the years since the financial crisis.

In a criminal guilty plea unveiled on Monday in New York Supreme Court, BNP admitted to conspiring to help clients evade U.S. sanctions against Sudan, Iran and Cuba. BNP also agreed to forfeit $8.9 billion, the largest criminal penalty in U.S. history.