S&P Global Ratings has revised its outlook on Berkshire Hathaway’s operating insurance subsidiaries to negative from stable and affirmed the AA+ financial strength and long-term counterparty credit ratings.

The revised outlook is part of S&P’s normal credit surveillance. Assessments are made based on the ratings agency’s capital model.

“The negative outlook is based on some uncertainty pertaining to the level of capital build-up necessary over the next one to two years to offset a material increase in risk exposure,” S&P says.

“Furthermore, the ratings could also be pressured if we view [Berkshire’s operating insurance subsidiaries’] overall creditworthiness to be weakening relative to its peers.

“Under our base-case scenario, we expect that the insurance operating companies will attain a very strong capital and earnings position supported by an extremely strong competitive position and strong earnings-generation capability in the next two to three years.”