Long scale (used in most of continental Europe and Latin America):
1 Billion = 1,000,000,000,000
Short scale (used in most English-speaking countries and Arabic-speaking countries):
1 Billion = 1,000,000,000
Using the short scale, $1 billion (in $100 bills) would take up about 400 cubic feet (11.33 cubic meters). That's a pile of cash about 8 feet wide, 8 feet long, and 6.25 feet tall. You'd need 18 such piles of cash to be $18 billion, so I think you are right, that wasn't $18 billion in that one picture, but I suppose they *might* have found a total of $18 billion (or $22 billion?) throughout the entire house?
Using the long scale, obviously the size of the pile would have to be 1000 times as big. so 400,000 cubic meters (11,327 cubic meters). Clearly, they didn't find that much cash in the house.