WASHINGTON (AP) - A person familiar with his plans says Rep. John Dingell of Michigan, the longest-serving congressman in U.S. history, will announce his retirement later today. The 87-year-old Dingell was first elected in 1955, filling the House seat vacated by his late father. The person was not authorized to speak publicly ahead of Dingell's announcement. He became the longest-serving member of Congress last year. His plans were first reported by The Detroit News and The Detroit Free Press.