The orientation offered will differ according to the hospital, their available resources, and the background of the incoming nurse. I've worked for large, level 1 teaching facilities with strict programs in place for both new graduates and nurses new to specialties that ranged from 4-12 months in duration, combining classroom and clinical hours on the floor. I've also worked for small, lower acuity facilities which basically offered two orientation days and three shifts on the floor with a preceptor.
Since you're coming from a stepdown unit, I'm assuming you have/will have many of the skills and check offs you will also need for ICU. That being said, you will still likely have an orientation 4-12 weeks with another nurse on the floor until you're comfortable to be on your own. Unlike new grad orientation, you will probably meet with your educator and preceptor to determine what you already know and what you will need help with using checklists and skill stations. You'll go through your orientation signing off these skills as you observe and then do them yourself with (hopefully) meetings every week or few weeks to discuss your progress.