Judging by size alone is a bad tactic in the animal kingdom. One of nature's deadliest creatures is the tiny poison dart frog. The wisdom of using bigness as a benchmark is dubious also in the financial world. But as regulators on both sides of the Atlantic seem apt to do so, it is worth asking when big becomes bad and to whom big poses a danger.

Assume that regulators wish to assess a banks' absolute size, or its size relative to economic output, rather than a measure of profitability, deposits or wholesale funding. There is still, points out JPMorgan, substantial scope for variation. Accounting discrepancies relating to netting of derivatives can exaggerate European banks' size relative to their domestic economies versus US peers. Measures of risk-weighted assets are notoriously variable, both cross-border and even between different home regulators. Meanwhile, it seems perverse that US regulators in particular are happy to see banks grow bigger, so long as they don't buy bulk. Growth in bank assets since 1992 has trailed revenue growth for their big international clients, JPMorgan notes.

Strange then that there has still been little discussion of cross-border co-operation in resolutions. Even the Federal Deposit Insurance Corporation, feverishly efficient at resolving US banks, has limited experience dealing with international exposure. In fact, notes the head of the International Monetary Fund, “globally myopic” measures are on the rise. In theory, an agreement that each country handled its share of a large failed bank's assets could lessen a home nation's burden. In reality, international business comes with heightened interconnectedness and risks of contagion – plus foreign governments loath to help dismantle an institution over which they had no oversight. As national reform efforts stall, international harmonisation remains a pipe dream.