What: Shares of Credit Suisse Group AG (CS) are plunging, down by more than 12% at 11:10 a.m. ET as the company reported disappointing earnings for 2015.

So what: Credit Suisse has been among the worst-performing banks in recent history, with shares plunging to prices not seen since 1991, according to Bloomberg. The company reported a full-year pretax loss of 2.4 billion Swiss franc, reflecting goodwill impairments (3.8 billion franc), restructuring costs (355 million franc), and litigation charges (821 million franc) for the full year.

The goodwill impairment is largely related to its 2000 acquisition of Donaldson, Lufkin & Jenrette (DLJ), an American investment bank.

Speaking to some of the challenges faced by investment banks in light of volatile markets, Credit Suisse CEO Tidjane Thiam noted that "clearly the environment has deteriorated materially during the fourth quarter of 2015 and it is not clear when some of the current negative trends in financial markets and in the world economy may start to abate."

Now what: The company's metrics were almost universally weaker than in the year-ago period. Tangible book value per share (which excludes the impact of goodwill impairments) declined 8%, assets under management dropped 11.3%, revenue fell 34%, and provisions for credit losses surged 77% year over year. 

Credit Suisse is overhauling its operations, moving away from investment banking and toward wealth management. It's also hoping to grow by getting smaller, identifying 4,000 positions that it plans to terminate to generate 1.2 billion franc in annual savings -- 34% of its 2018 goal. Investors are clearly worried that a turnaround will take longer than the bank suspects, selling off the stock in active trading today.