The Treasury began with a sale of 553.8 million shares of the company into which it had invested $182.3 billion to keep it from collapsing in the heat of the financial meltdown of 2008 and 2009.
The shares were priced at $32.50 apiece, with expected proceeds of $18 billion. However, with an over-allotment in effect, the Treasury's take was expected to reach $20.7 billion, the department said in a statement.
The sale was also expected to disperse 636.9 million shares that would reduce the department's holdings of AIG from 53.4 percent to 15.9 percent.
In total, the Treasury said its return on the $182.3 billion investment had now come to $197.4 billion, "representing a positive return of $15.1 billion to date," the department said.