I think two different accounting methods are being conflated here which leads to the huge $3B vs $18B difference. Congress periodically authorizes spending for military aid to Israel and other countries. Later, the executive branch actually disburses that aid. In recent years, the US has on average given Israel $3B. This year, congress authorized an additional $18B to be disbursed through 2026 - which is what recent news stories about US giving Israel $18B are referring to, as far as I know. You would end up double-counting every dollar, if you did the math that way on an ongoing basis.

But if you know of a clean source of data on the actual amount of aid provided each year, that would be useful. I’d guess the number this year would be a lot more than $3B given the physical reality of tons of expensive offensive and defense missiles fired.