When Berkshire Hathaway announced the acquisition of MidAmerican Energy in 1999, Warren Buffett hailed the Iowa gas and electric utility as squarely in the conglomerate’s “sweet spot”.

Unheralded at the time, the $2bn transaction catapulted Buffett into the energy business, kicking off a quarter of a century of dealmaking that has transformed Berkshire into a major player, operating across 28 states, transporting 15 per cent of America’s natural gas and serving 13mn customers.

The $138bn of assets owned by its subsidiary, Berkshire Hathaway Energy, are varied but the appeal of the businesses — and their place within Berkshire — have gone unquestioned. Its utilities, accounting for the bulk of BHE’s assets, boast the economic moats against competition prized by Buffett and have long been an attractive home for the cash that the conglomerate generates.