The NAB is selling down more of its interest in the South Dakota-based Great Western Bank in a share offering.
The offering will see NAB reducing its holding to 2.2%, or to zero if there is sufficient demand, from 28.5%.
The move is part of a global strategy of divestment to concentrate on core business in Australia.
As part of the latest deal, Great Western Bank itself will buy about $60 million of common stock from the NAB.
The bank will raised a total of about $US385 million from the current sale. NAB has been progressively selling down the US agribusiness bank it bought in 2008 for about $1 billion.
NAB had to raise the capital to meet UK regulatory requirements to meet potential compensation costs to customers who were wrongly sold financial products.
In the demerger and float, NAB aims to sell 80% to current shareholders and the rest to institutions.