Русско-англо-русский юридический словарь

The "too big to fail" theory asserts that certain corporations, particularly financial institutions, are so large and so interconnected that their failure would be disastrous to the greater economic system, and that they therefore must be supported by government when they face potential failure. (Wikipedia)

A systemically important financial institution (SIFI) is a bank, insurance company, or other financial institution whose failure might trigger a financial crisis. They are colloquially referred to as "too big to fail". (Wikipedia)