Creating a new list with new second element

Given data={{1, 34}, {2, 54}, {3, 66}, {4, 77}, {5, 92}}, I would like to create a new list such that

{{1, 34}, {2, 54-34}, {3, 66-54}, {4, 77-66}, {5, 92-77}}  

which is {{1, 34}, {2, 20}, {3, 12}, {4, 11}, {5, 15}.