1. A system for migrating documents from a source enterprise content management system to a target enterprise content management system, the system comprising: a release component configured to establish a source connection with a source enterprise content management system using a source connector that interfaces with the source enterprise content management system, and release, from the source enterprise content management system over the established source connection, documents and metadata that correspond to the released documents; an electronic data storage unit configured to temporarily store the released documents and the released documents metadata; a loading component configured to access, from the electronic data storage unit, the released documents and the released documents metadata, map source metadata attributes from the released documents to target metadata attributes, establish a target connection with a target enterprise content management system using a target connector that interfaces with the target enterprise content management system, and load, over the established target connection to the target enterprise content management system, the released documents and the mapped metadata, the source metadata attributes corresponding to attributes of the source enterprise content management system and the target metadata attributes corresponding to attributes of the target enterprise content management system; and a batch engine configured to control the release component to release, from the source enterprise content management system, batches of documents and metadata, control the loading component to load, to the target enterprise content management system, batches of documents and metadata that have been released from the source enterprise content management system, and store migration records that describe migration operations from release from the source enterprise content management system through loading to the target enterprise content management system.