Roughly 45 firms working on Puerto Rico's debt restructuring, including top-tier firms such as Proskauer Rose, Norton Rose Fulbright, DLA Piper and Greenberg Traurig, have billed more than $400 million collectively in the two years since the restructuring began.

Firms in the Am Law 100 account for more than $160 million in fees and expenses.

Analysts estimate the total amount of debt tied to Puerto Rico's restructuring totals more than $100 billion, far exceeding the second-largest municipal reorganization—Detroit—estimated at $18 billion.