Dimon keeps track of his bank’s business by scribbling on a sheet of paper in his coat’s breast pocket. The notes are divided into two columns: one for “things I owe people” and the other for “things people owe me,” according to people who’ve worked with Dimon. “He carries it until he’s used every square centimeter and the paper is old and crinkled,” says Michael Welborn, the former head of retail banking at Bank One, which Dimon ran before he merged it into JPMorgan Chase. “He is unbelievable at grasping details and the big picture at the same time.”