The three-member Public Utility Commission of Texas on Thursday unanimously declined to accept the agreement as being in the public interest — a requirement for the deal. Financial concerns were raised.
Oncor is an electric transmission and distribution provider serving 10 million customers across Texas. It's the state's largest regulated utility.
The parent of Oncor, Energy Future Holdings, filed for Chapter 11 bankruptcy protection in 2014. Oncor was not part of the bankruptcy reorganization.
NextEra Energy is based in Juno Beach, Florida, and is the parent of Florida Power & Light Co.
A 2016 effort to acquire Oncor, backed by the Ray Hunt family of Dallas, also faltered.