The infant was in a car seat inside the home at the time of the attack Thursday, The Detroit News reported.
The child's mother, who is 24, carried the baby in a car seat into the building where she was temporarily staying with a friend, police said.
The mother placed the car seat on the floor, walked away briefly and when she returned the dog was attacking the child, police said.
The baby died at a hospital.
Police removed the dog, which officers were told had never shown any signs of aggression.
A neighbor, Rosa Bell, contested that statement. She said the dog would growl at her and "look at us like it was going to attack us."