Greece vs Puerto Rico and what's "systemic."

How is a Greek default different from a Puerto Rican default?

Answer: because Puerto Rico doesn't have its own banking system. It can't shut down banks. Banks in Puerto Rico are not loaded up on Puerto Rico debt, so depositors are not in danger if the state government defaults.

Puerto Rico, like Greece, uses a common currency. But there is no question of PRexit, that people wake up one morning and their dollar bank accounts are suddenly PR Peso bank accounts. So they have no reason to run and get cash out.

Banks in New York are also not loaded up on Puerto Rico debt. US bank regulators haven't said that those banks can pretend Puerto Rico debt is risk free.

If a Puerto Rican bank fails, any large US bank can quickly take it over and keep it running.

A Puerto Rican government default will be a mess. Just like the default of a large business in Puerto Rico. But it will not mean a bank run, crisis, and economic paralysis.

So here is a big lesson of the Greek debacle: In a currency union, sovereign debt must be able to default, without shutting down the banks, just as corporations default. Banks must not be loaded up on their country's sovereign debt. Bank regulation must treat sovereign default just like corporate default. It can happen, and banks must diversified and capitalized to survive it.  Banks must be free to operate across borders.  A common currency needs a firm commitment that it will not be abandoned.

In financial regulation, the big debate rages over what is "systemic,"  with the latest absurd idea to extend that designation to equity asset managers. (More later.) All that discussion starts with statements that  sovereign debt or anything backed by sovereign debt or sovereign guarantees is safe and per se not "systemic." Sovereign debt still counts as risk free in almost all banking regulation.

Greece should reinforce the lesson: Sovereign debt is a prime source of "systemic" danger. That is especially true of small governments in a currency union. A government is just a highly leveraged financial institution and insurance company.

Wrong answers:

- Fiscal union. The US is not necessarily going to bail out Puerto Rico. Or Illinois. Or their creditors. People keep saying a currency union needs fiscal union, but it is not so.

- National deposit insurance is really not central either. The banks operating in Puerto Rico are not in danger, so they don't need deposit insurance protection.

Update: A colleague pointed me to this excellent article on banks holding their own sovereign debt by Lucrezia Reichlin and Luis Garicano.