Federal Reserve quantitative easing works in two ways: its fiercely debated near-term economic effects and a longer-term impact on government debt that Chairman Ben Bernanke isn't eager to discuss. In some ways, the latter is easier to quantify. By year-end, Fed purchases of more than $2 trillion in Treasury and mortgage-related securities will have shaved about $400 billion from the rising public debt load, an IBD analysis finds.