Detroit Edison was part of a large holding company called North American Edison Company. North American's stock had once been one of the twelve component stocks of the May 1896 original Dow Jones Industrial Average. North American Company was broken up by the Securities and Exchange Commission, following the United States Supreme Court decision of April 1, 1946.
After that Detroit Edison operated independently, and publicly traded on the New York Stock Exchange, under the ticker symbol DTE through the mid 1990s. In early 1996, it became an operating subsidiary of the new holding company, DTE Energy Company, which replaced Detroit Edison Company on the stock exchange, and took over the trading ticker symbol.