Warren Buffett disclosed that he had converted 1,800 Class A shares, worth about $1.35 billion, into the company's lower-priced B shares and donated them to four of his family foundations.

Warren Buffett sought to allay investor concerns about his upcoming retirement in a letter to shareholders on Monday.

In one of his final missives as the company’s leader, Mr. Buffett said he would accelerate his plans to disburse his fortune to his children’s foundations.