It serves over 10.3 million customers throughout Peninsular Malaysia (except Sarawak) and the East Malaysian state of Sabah through Sabah Electricity Sdn Bhd. 

TNB’s core activities are in the generation, transmission and distribution of electricity. Other activities include repairing, testing and maintaining power plants, providing engineering, procurement and construction services for power plants related products, assembling and manufacturing high voltage switchgears, coal mining and trading.

TNB is one of the 10 companies under Khazanah Nasional, Malaysian sovereign wealth fund and also the largest publicly-listed power company in Southeast Asia with MYR 182.60 billion worth of assets.

The TNB Group has a complete power supply system, including the National Grid which is energised at 132, 275 and 500 kilovolt (kV), with its tallest electricity pylon in Malaysia and Southeast Asia being the Kerinchi Pylon located near Menara Telekom, Kerinchi, Kuala Lumpur. 

TNB, through its subsidiaries, is also involved in the manufacturing of transformers, high voltage switchgears and electrical cables, consultancy services, architectural, civil and electrical engineering works and services, repair and maintenance services and fuel undertakes research and development, property development, and project management services.

According to Wikipedia