The platforms of both US political parties now favour a return to the Glass-Steagall separation of commercial and investment banking. Investors in the shares of major banks won’t be cheering.

Among the large universal banks, JP Morgan would likely be hit hardest, ironically because it has done the best job creating an efficient whole. That isn't a big surprise. The bank estimates it earns $15 billion a year in extra revenue from cross-selling between units, and saves $3 billion in costs.