Szoka died of natural causes Wednesday night at Providence Park Hospital in Novi, Mich., the Archdiocese of Detroit said in a statement Thursday.
"We mourn the loss of a dedicated shepherd," said Detroit Archbishop Allen Vigneron, who served as a priest under Szoka in the 1980s. "For 60 years, Cardinal Szoka gave himself totally to his priestly service of Christ and his church. He has gone home to the Heavenly Father with our prayers."
Szoka received his first assignment as a priest in 1954, as associate pastor of a parish in Michigan's rural Upper Peninsula. By the early 1990s, he was the Vatican's point man for finance. And by the end of that decade, he was running one of the world's smallest countries: Vatican City.
In between, Szoka honed his administrative skills as the first bishop of the Diocese of Gaylord and, later, archbishop of Detroit.
Edmund Casimir Szoka was born Sept. 14, 1927, in Grand Rapids to Polish immigrants.
Szoka's leadership of the Detroit archdiocese was highlighted by Pope John Paul II's 1987 visit to Michigan. Szoka also endured criticism for closing more than 30 small parishes in Detroit. John Paul II made him a cardinal in 1988.
Szoka grew close to the Polish-born John Paul II, spending Christmas and Easter dinners with him, prayed for the pontiff at his deathbed, and led a rosary in St. Peter's Square the night he died.
In 1990, Szoka became president of the Prefecture for the Economic Affairs of the Holy See, which audits Vatican accounts, approves or disapproves budgets, and handles major financial transactions such as buying and selling property.
By demanding strict financial accountability from within and requiring regular contributions from dioceses worldwide, the Vatican operated in the black under Szoka's leadership.
Szoka said his nine years as Detroit archbishop and his earlier time in the Marquette diocese helped him become financially responsible.
"It helped me learn a lot of fundamental and basic things," he once told The Detroit News.
As governor of Vatican City, Szoka held executive and legislative power in the city-state. He managed annual budgets and oversaw the famous collection of Vatican buildings and artworks.
"At the time I was nominated, I worried about taking on an administrative post at my age," Szoka told Inside the Vatican magazine in 1998. "I was 70 ... but after a few days in it, I felt fine — challenges inspire new energies."
Pope Benedict XVI accepted Szoka's resignation a day after his 79th birthday in 2006.
After his retirement from active ministry, Szoka lived in the Detroit suburb of Northville.
A funeral Mass for Szoka is scheduled for 11 a.m. Tuesday at the Cathedral of the Most Blessed Sacrament in Detroit, with burial at Holy Sepulchre Cemetery in suburban Southfield, according to the Archdiocese of Detroit. Visitation is set for Sunday through Tuesday at the cathedral.