How do I enter that amount in TurboTax without a 1099R? You don't. Since the total your first RMD isn't required until 4/1/18, you'll just report the $20,000 that was distributed in 2017 reported on your 1099-R. Since there was no RMD requirement for 2017, you fulfilled the requirement, if asked.
Your RMDs for 2018 and later years must be completed by year-end. You may have an RMD for 2018 of around $24,000 again, but that will be in addition to the $4,000 Jan 1, 2018 distribution. Please feel free to post any additional details or questions in the comment section.
