Here is a good read I think on that subject.

[Snip] January 4, 2017 "HOW MANY ARE NEWLY INSURED AS A RESULT OF THE ACA?"

According to the HHS report, 17.7 million people are newly insured since October 2013 (primarily through the Exchanges and Medicaid), and 2.3 million are young adults who benefitted from the provision allowing them to remain insured as a dependent on their parents’ health insurance until age 26, which took effect in 2010 ... An estimated 4.9 million individuals now enrolled in Medicaid were previously eligible for the program. Of the estimated 5.8 million newly insured in the individual market, at least 1 million are not receiving ACA subsidies. While some have gained employer-sponsored insurance (ESI), as many as 5.9 million may have lost ESI because of the ACA...

Read more: 
https://www.americanactionforum.org/insight/20-million/