The New York Times’s Alexandra Stevenson identified this work by Willem de Kooning, Untitled III  as the painting mentioned in Steven Mnuchin’s financial disclosure. The work was owned by L & M Arts and bought from that dealer by the 2014 consignor at Christie’s.

Whether Mnuchin bought the painting for himself or, more likely given the financial disclosure for the Offiice of Government Ethics, he provided financing to Mnuchin Gallery, is not known from the press accounts. Here’s Bloomberg’s mention of the work:

The financial disclosures, which Mnuchin signed Dec. 16, show that his income for 2016 was as much as $24 million, based on a calculation by Bloomberg. Mnuchin also owns a multi-million-dollar stake in a Willem de Kooning oil painting.

Mnuchin to Divest Stakes in 43 Investments to Avoid Conflict  (Bloomberg)