Steven Mnuchin explains why nearly $1.5 trillion worth of $100 bills reportedly disappeared

Mnuchin pointed to the negative interest rates causing people to turn to American dollars as a solid investment.

"The dollar is the reserve currency of the world, and everybody wants to hold dollars," Mnuchin said on "Lou Dobbs Tonight." "And the reason why they want to hold dollars is because the U.S. is a safe place to have your money, to invest and to hold your assets."