How liquidity forecast id gets generated?

In the data source "Liquidity Forecast",i could find a liquidity forecast id for all the payment related documents which are created through different business objects such as "Outgoing Check", "Incoming Check","Bank Payment Advice" etc.How can we correlate these liquidity forecast ids with respect to the document ids generated in these different business objects or how can we extract this liquidity forecast id based on document ID. Can anyone please help me in figuring this