Morningstar plans to acquire debt-rating agency DBRS for $669 million in a bid to bolster its credit-ratings business, Morningstar said Wednesday in a news release. The acquisition by the Chicago-based investment research firm will "expand global asset class coverage and provide an enhanced platform for providing investors with leading fixed-income analysis and research," the news release said. Based in Toronto, DBRS is the fourth-largest credit-ratings agency and rates over 2,400 issuer families and almost 50,000 securities worldwide.