McGraw-Hill Companies Inc is in advanced talks with CME Group Inc to merge the S&P Index business with CME's Dow Jones Indexes, a source familiar with the situation said Thursday.

Under the terms of the deal being discussed, McGraw-Hill would own the majority of the joint venture and manage it, while CME would own about 25 percent, the source said.

The deal, however, has not been finalized and the terms could change, the source said.

McGraw-Hill and CME declined to comment on the news, which was first reported by the Wall Street Journal.