From a bank's perspective, a loan is an investment/asset, so should probably be a part of what is called M2 or M3 money.

EDIT: Wikipedia seems to agree: https://en.wikipedia.org/wiki/Money_supply#Fractional-reserv...

> Whenever a bank gives out a loan in a fractional-reserve banking system, a new sum of money is created. This new type of money is what makes up the non-M0 components in the M1-M3 statistics.