American International Group said Monday that it had used $4 billion from a recent debt sale to pay back the U.S. government, marking the single largest cash repayment so far from the bailed out insurance giant.

The money came from a $4.4 billion debt sale completed last week by AIG’s massive aircraft leasing unit, International Lease Finance Corp. ILFC returned $3.95 billion to its parent company, which promptly used the proceeds to pay down outstanding loans from the Federal Reserve.

“This is continuing tangible evidence of AIG’s progress in repaying the American taxpayers,” chief executive Robert Benmosche said in a statement. “AIG is getting stronger every day. We still have more work to do, but we will finish the job and make sure we repay the American taxpayers.”

The payment reduces AIG’s outstanding balance on the Fed loans to about $21 billion, including interest and fees. If AIG fails to repay the loans in full, the Fed’s losses will ultimately fall on taxpayers. The Fed also invested tens of billions of dollars more to help AIG rid itself of troubled derivatives contracts that were bleeding it dry.