trade derivatives. This provision almost derailed the bill following vehement objections from New York Democrats. Ms. Lincoln worked out a deal in the early hours of Friday morning that would allow banks to trade interest-rate swaps, certain credit derivatives and others—in other words the kind of standard safeguards a bank would take to hedge its own risk.

Banks, however, would have to set up separately capitalized affiliates to trade derivatives in areas lawmakers perceived as riskier, including metals, energy swaps, and agriculture commodities, among other things.

A panel of 43 lawmakers spent two weeks reconciling differences between a bill that passed the House in December and the Senate in May. They concluded their negotiations along party lines at a little after 5 a.m. ET in a Capitol Hill conference roommarked by tension, levity and exhaustion. Senior administration officials, including Treasury Department Deputy Secretary Neal Wolin, arrived late in the afternoon to try and quell the feud between the New York delegation and Ms. Lincoln.

Major components of the bill, including the derivatives provisions, were negotiated in the hallway of the Dirksen Senate Office Building as the clock neared midnight. At one point, after hearing of an offer from Senate Democrats, Rep. Melissa Bean (D., Ill.) exclaimed: "Are you flipping kidding me? Are you flipping kidding me?"

Democrats hailed the agreement as a tool to prevent the kind of taxpayer-funded bailouts that stabilized the economy in 2008 but left divisive scars. Many Republicans said the bill could have unintended consequences, crimping financial markets and access to credit.

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