HAVANA (AP) — Raul Castro is stepping down from Cuba's presidency, but he isn't giving up power.

The 86-year-old former guerrilla remains head of Cuba's Communist Party, a position that leaves him with broad authority — including much oversight of the man who is replacing him as president. He is expected to hold the position until 2021.

Raul Castro's official title will remain first secretary of the Communist Party, heading the elite 17-member Political Bureau and the broader Central Committee. Since committee members are elected from lists approved by the leadership, there is no real opposition, though members do debate important issues.

Cuba's single-party system gives the Communist Party a role vastly more important than in any multi-party country, and it's often hard to tell where the party stops and government begins. Senior government and party positions often overlap.

The constitution defines the party as "the superior guiding force of society and the state," directing it to organize society toward the construction of socialism.

In practice, party officials oversee or work with government authorities on every level, including the military. While the new president is legally commander in chief, Raul's influence is imbued throughout the institution that he led as defense minister for nearly half a century.

The party runs vast organizations that coordinate activities for nearly every Cuban child and student. Workers are part of the Communist Party labor union. Every major newspaper and magazine is run by the party.