He also noted that previous financial regulations were "half a century or more old," and that the financial crisis emerged from an industry that was poorly regulated and not well understood.
Lew's comments came during an interview that also touched on immigration reform, revelations that the Internal Revenue Service had singled out conservative groups for extra scrutiny and the broader economic recovery.
Some legislators worry that more needs to be done.
Sens. Sherrod BrownSherrod BrownOvernight Finance: Dems seek probe of acting SEC chief | Defense hawks say they won't back short-term funding | Senate seen as start point for Trump infrastructure plan | Dems want more money for IRS Senate Dems call for investigation of acting SEC chairman Dems wait for GOP olive branch after ObamaCare debacle MORE (D-Ohio) and David VitterDavid VitterFormer GOP rep joins K Street lobbying firm Capitol Counsel Lobbying World Mercury brings on former Sen. Vitter, two others MORE (R-La.) introduced legislation in April to tighten controls on big banks. The bill would increase the amount of money most banks need to hold in reserve, limit financial institutions' ability to transfer money between affiliates and reduce burdens for small institutions.