Berkshire Hathaway revealed four new investments Thursday in steelmaker Nucor, insurer UnitedHealth and two of the nation's biggest homebuilders — Lennar and DR Horton — but it's not clear if the investments are big enough to ensure that legendary investor Warren Buffett handled them.

Warren Buffett's Berkshire Hathaway increased its holdings in UnitedHealth Group stock, and also added positions in D.R. Horton, Lamar Advertising, and Nucor.

Warren Buffett's Berkshire Hathaway revealed a new stake in troubled insurer UnitedHealth, according to a regulatory filing. The Omaha-based conglomerate bought more than 5 million shares in the health care firm for a stake worth about $1.