ALBANY, N.Y. — Fidelity Investments said Friday it will buy back $300 million worth of auction-rate securities from its customers, becoming the first major retail brokerage to make restitution in a wide-ranging investigation.

Fidelity is the first so-called "downstream" distributor — rather than an underwriter — to settle an auction-rate securities probe, even though Fidelity didn't conduct auctions, New York Attorney General Andrew Cuomo said.