The lender blamed the heavy losses on "temporary valuation effects" and "a higher risk provision booked on account of the pandemic".
The group has not provided a firm forecast for 2020. "In view of the uncertainty about the further development of the pandemic, it is difficult to provide a concrete outlook," it said.
Commerzbank, which has been partly state-owned since the financial crisis of 2008, had been in talks to merge with crosstown rival Deutsche Bank.
But the bid to join forces failed early last year, leading the bank to slash 4,300 jobs to bring its headcount down to just over 40,000.
Commerzbank reported net profit of 644 million euros for 2019.