Inter-American Development Bank General Capital Increase Act of 2020 This bill requires the President to support and coordinate diplomatic engagement to secure a 10th general capital increase for the Inter-American Development Bank (IDB) and to support the creation of an environmental fund and financing facility at the IDB. The bill also authorizes the U.S. Governor of the IDB to vote in favor an $80 billion increase in the capital stock of the IDB and to subscribe on behalf of the United States to additional shares of this capital stock.