I heard you are screaming, why there is no “Document ID” field.
Because the Document ID enable/disable is run by Timer job.
The timer jobs are located on the Central Admin site under Monitoring > Review job definitions. Make sure the view in the top right is selected for All, then scroll down and find Document ID enable/disable job for your web application in question > click the title and hit Run Now. Go back to the Job Definitions list and now scroll down and find Document ID assignment job for your web application in question > click the title and hit Run Now.
Click Running Jobs on the left nav and you should see the progress of the assignment job (it may take awhile as this is the job that assigns IDs to your existing docs). Keep hitting refresh until the job disappears, meaning it finished.
Go back to your library where you have just assigned doc ids and under the Library tab in the ribbon UI, click Modify View, scroll down find and check Document ID (linked to document). Click Ok and you should now see your documents with the Doc ID column displaying your proper ID charset.