A divided Commodity Futures Trading Commission delivered a year-end victory for Wall Street, easing up on requirements that banks set aside cash as a cushion against the risk of certain swaps trades going bad.

The move came as the CFTC adopted final rules on collateral, known as margin, required for certain types of swaps. The changes save firms from having to set aside billions of dollars that could otherwise be used for more profitable purposes. But they buck warnings from Democrats, including Massachusetts Senator Elizabeth Warren and Ohio Senator Sherrod Brown, not to scale back the requirements.