Do you think the US Mint is a bad source?
If so this link provides the answer:
http://www.usmint.gov/about_the_mint/fun_facts/index.cfm?flash=no&action=fun_facts13
No that’s no the answer. Too vague. Yes, it is close to a primary source, but it does not specifically speak either to ownership or audit records.
I was taught to read financial statements from the back to the front. The last thing in a financial is the auditor’s statement — who, where, when, how.
That US Mint web site is just a blurb.
About $150 billion.