FIVE years is the length of a modern British Parliament and one of Stalin’s economic plans. Apparently, it is also the time needed to bring in a new American financial regulation. When the Dodd-Frank act was passed in 2010, the so-called Volcker rule was seen as one of its key provisions. But the rule only formally took effect on July 21st this year.

The pertinent clause of Dodd-Frank amounts to all of 165 words (with the key points covered in 40). Banks are banned from two activities: proprietary trading and ties (through investment and relationships) to hedge and private-equity funds. Putting that into practice involved a collaboration of five regulatory agencies: the Federal Reserve, the Securities and Exchange Commission, the Commodity Futures Trading Commission, the Federal Deposit Insurance Corporation and the Office of the Comptroller of the Currency (OCC). This group produced an 891-page preamble leading to a 71-page rule, all of it written in dense bureaucratese.

The aim of the rule is to stop banks (and their worldwide affiliates) with the implicit support of the American government from indulging in speculation and becoming enmeshed in conflicts of interest. In reality, distinguishing such activities from more beneficial financial operations has proved daunting. “It’s impossible for banks to know if they are completely in compliance with the rule, because there are so many interpretive questions remaining,” says Gabriel Rosenberg of Davis Polk & Wardwell, a law firm.

Exceptions have been carved out for market-making, risk-mitigation, underwriting and (surprise!) trading American government bonds. But complying with the rule has forced banks to close or sell whole divisions. Goldman Sachs has closed down two proprietary-trading operations without much ado, and wound down various funds in which it co-invested with clients, without suffering any visible calamities. JPMorgan Chase has done the same.

Banks have created compliance systems designed to ensure that every single transaction meets the Volcker standard. This has not been easy. Every time a bank buys or sells a security it is in effect taking part in a proprietary trade. This is also true, for example, when it expands its holdings of foreign currency in anticipation of demand. Bank examiners will not only have to judge assets and liabilities, but also intentions. Some foreign banks, judging that they simply lack the political clout to navigate such a complex regulatory environment, have cut back their American operations, to the delight of their American competitors.

Has this upheaval been worth it? Although many provisions of the Dodd-Frank act require cost-benefit analysis, the Volcker rule does not. The OCC has provided some cost-benefit estimates, which could be the basis of further investigation.

The benefits, the OCC concludes, are largely unquantifiable but include better supervision, better risk management, greater safety, fewer conflicts of interest and the hope that a crisis will be avoided. Compliance costs, inevitably, come with a more explicit price tag. The OCC reckons the seven “market-making” banks (ie, the biggest) will have collectively spent over $400m in 2014 and a bit less going forward. The OCC’s annual supervision costs will rise by $10m. Another 39 banks it examines will have additional direct costs of only several million dollars a year.

The largest costs, however, like the biggest benefits, can be hard to quantify. There may be less competition for large banks because smaller rivals will want to avoid the steeper compliance costs. With banks now forced to limit their efforts to make markets in securities only to activities that can be tightly linked to customers, their inventory of securities has declined.

Reduced dealer inventories in the corporate-bond markets has already become the subject of investor concern. They reduce the possibility of big bank losses in a crunch, but they also decrease market liquidity. Investors have usually required a higher return to compensate for holding less liquid securities, raising the cost of capital for some companies and making it harder for others to raise money. Perhaps the most likely outcome is that trading shifts to unregulated firms in the “shadow banking” sector. Instead of being extinguished, financial risks may just become harder to spot.