Berkshire Hathaway said in documents filed with the U.S. Securities and Exchange Commission that it signed the financing deal with JPMorgan Chase and Wells Fargo on November 18.

Buffett has said Berkshire, which is based in Omaha, plans to borrow half of the $16 billion cash needed for the deal, and pay back the loan over three years.

Berkshire has agreed to pay $100 a share in cash and stock for all the Burlington Northern shares it doesn't own. Berkshire holds a 23 per cent stake in the railroad, which is based in Ft. Worth, Texas.

The deal is expected to be completed early next year if shareholders and regulators approve.