A-Train HX

The achievement tracks interest paid on loans. The amount you can borrow is based on your total assets, so this is easier to do later in the game. Open the Market menu, use to select the bank, and change the amount of the loan to the maximum of $1 billion. Take out the loan, repay it immediately, rinse and repeat until the achievement unlocks.

If you are following the road map, you should do this after clearing the scenario on your first map.