US power network

I live in the UK so understand UK utilities and national electricity grid etc. I am less knowledgeable about the US. I know that there are the big US power companies such as PG&E. Are these the main US power companies. I assume that there is no US equivalent of National Grid? So if the US was to invest heavily in power generation and network who would be the main beneficiaries? Would it be companies such as PG&E, construction companies (who), new providers/independent companies…

Also which are the main US based gas exploration and production companies if generation was with gas?