People familiar with the structure of the agreement said that they were non-recourse, meaning that Mr Wieses other assets and holdings could not be seized by the banks to pay back the loan.
Given the sudden and unexpected drop, the normal triggers built into such structures to protect banks from a loss did not kick into place.
BofA has the largest net exposure to the loan of between 300m and 400m to Mr Wieses loan, while Citigroups exposure is more than 200m, according to several people following the situation.
Goldman Sachs and HSBC are exposed to about 120m each, while BNP Paribas has roughly 100m. JPMorgan Chase, Nomura and UBS are also exposed, these people said.
Quele: www.ft.com/content/86c342d2-e0f4-11e7-8f9f-de1c2175f5ce