People, don't be misled by 13F SEC Filings reported by hedge funds and institutional investment managers every quarter. They don't have to report short positions or naked credit default swap exposure (credit insurance) against underlying long positions. Meaning 10 million shares of Company X might just be part of a large net short position. This is an interesting comment on the potential nature of Paulson's MGM holding this Q.
13F-Reports are filed quarterly by institutional investment managers (managing more than $100 million) less than 45 days after the quarter ends at SEC.gov. 13D-Reports are filed when institutional investment managers own 5% or more of a company within 10 days of the purchase. They must report material changes (acquisitions or dispositions) greater than 1% of the holding.