Are there too many cooks? as five federal agencies begin implementing the massive—and massively complex—Volcker Rule, financial institutions have one overriding question: Who will they answer to? Megabanks fear that conduct that one regulator blesses another will forbid, creating a legal minefield when it comes to proprietary trading.

In February the agency heads offered alarmed members of Congress a three-word panacea: interagency working group.