20% out of cases which had an outcome.
This almost surely means you need to have been diagnosed with a test to be included in this statistic. Given the shortage of testing generally, only the more serious cases even had a test ordered. So it's likely a 20% death rate out of the cases with more pronounced symptoms.
Mortality rate has been quoted at anywhere from 0.5% (Germany) to 0.6% (Korea) to 7% (Italy). The difference is likely, from what I've heard, based on population demographics (age, weight, health) and strength of the healthcare infrastructure.