Cuba's former President Fidel Castro (R) talks with Ramon Labanino (L) and Gerardo Hernandez, two of the "Cuban Five", in Havana in this picture provided by Cubadebate. [Photo/Agencies]

In exchange, Cuba freed a Cuban man who spied for Washington and spent nearly 20 years in jail. In addition, Cuba freed imprisoned American aid worker Alan Gross on humanitarian grounds plus 53 people that United States considered political prisoners.

Fidel Castro stepped down from power in 2008, handing off to his younger brother Raul, 83. Fidel Castro occasionally writes a column and is seen in the official media receiving dignitaries at his Havana home, but he has not been spotted in public since Jan. 8, 2014.

Fidel Castro's current role in policy-making is unknown. Many Cubans presume Raul Castro consults with his brother on major decisions, and Fidel Castro's long absence after the announcement raised questions about his health and whether he agreed with ceasing hostilities with the Americans.

Intelligence agents Gerardo Hernandez, 49, Antonio Guerrero, 56, and Ramon Laba?ino, 51, came home on Dec. 17 after serving 16 years in US jails.

Two others, Rene Gonzalez, 58, and Fernandez Gonzalez, 51, had previously returned after fulfilling their sentences.