On Tuesday morning, regulators released their draft of the regulations needed for enactment of the Volcker Rule, aiming to prevent banks from engaging in speculative trading. Over the course of the morning and early afternoon, the five agencies involved approved the regulations, making the Volcker Rule the fully enforceable law of the land.

Wall Street seemed to have liked the final details of the rule. Two of the firms that have the most to lose from an aggressively enforced Volcker Rule gained on the day, with Goldman Sachs shares up 1.23 percent and Morgan Stanley shares up 1.25 percent (this on a day that the Standard & Poor's 500 index was down 0.32 percent).

But note that other banks weren't really affected. Shares of Wells Fargo, Bank of America and Citigroup all fell alongside the broader market.

It's hard to disentangle why any company's shares move on any given day, but this is a big enough move that it suggests investors concluded that the trading profits of Goldman and Morgan won't be quite as badly damaged as they had supposed.