TIAA-CREF is buying Nuveen Investments in a deal valued at $6.25 billion.

TIAA-CREF is leading provider of retirement and financial services. Chicago-based Nuveen is a diversified investment management with about $221 billion under management.

TIAA-CREF is buying Nuveen from an investor group led by Madison Dearborn Partners. Nuveen will operate as a separate subsidiary within TIAA-CREF’s Asset Management business. John Amboian will remain the chief executive officer of Nuveen, and Nuveen’s current leadership and key investment team will stay in place, TIAA-CREF said in a news release.

“We are delighted to partner with TIAA-CREF, which stands among the most highly respected financial institutions and possesses an unparalleled pedigree in retirement services and investment management,” Amboian said in a prepared statement. “The clients of Nuveen, and each of our investment affiliates, will benefit from TIAA-CREF’s support of our multi-boutique approach and from the continuity of our client services, our brands and our professionals, whose interests will remain strongly aligned with our long-term success.”

The boards of directors at TIAA-CREF and Nuveen have unanimously approved the transaction. The companies expect to complete the deal by the end of 2014.