"They know each other well, they like each other well, they both have their areas of specialty", he said.
The 87-year-old Buffett named Gregory Abel as Vice Chairman of the company's noninsurance businesses; he is also Chairman and CEO of Berkshire Hathaway Energy Co.
Buffett told CNBC that elevating Abel and Jain would have also made sense five years ago.
It was Munger's idea for Abel, Jain, and himself to all have vice chair titles, Buffett said. "Berkshire will operate best if its CEOs average well over 10 years at the helm".
"Our directors believe that our future CEOs should come from internal candidates whom the Berkshire board has grown to know well", he said.
The company said Wednesday that Buffett and Charles T. Munger, Berkshire Hathaway's vice chairman, will retain their positions on the board.
"When it happens or how or anything else, I don't know", he added in an interview on CNBC's "Squawk Box" from Omaha, Nebraska.
In late-morning trading, Berkshire Class A shares rose $2,010 to $306,530 and its B shares rose $1.61 to $204.63.
Abel joined Berkshire Hathaway Energy Co.in 1992 and now serves as its Chairman and CEO. His Iowa-based unit now runs several power companies in the United States, Canada and Britain, as well as natural gas pipelines and solar and wind farms. Buffett had refused to name them, but investors who follow Berkshire had long included Jain and Abel on their short lists.