Citigroup Inc., the nation’s biggest financial institution, on Friday said it will pay $2 billion to settle a class action lawsuit over its role in the sale of Enron Corp. stock and bonds before the energy company’s collapse that cost investors billions of dollars.

Under the settlement, Citigroup said it will distribute the payment to investors who bought publicly traded equity and debt securities issued by Enron and its related units between Sept. 9, 1997, and Dec. 2, 2001.