Warren Buffett can’t take all the credit for Berkshire Hathaway’s earnings nearly doubling last year, a fact the 87-year-old billionaire readily concedes.

While net income at the Omaha, Neb.-based conglomerate rose 87 percent to $44.5 billion, “a large portion of our gain did not come from anything we accomplished at Berkshire,” he wrote in his yearly letter to investors, a missive devoid of the political and economic commentary he often includes.