Insurance  coverage for trans people has always been tricky.  In some cases so many hurdles and coverage exclusions existed that it was common for those in the community to expect almost everything they wanted or needed in way of health care would be covered only via private pay arrangements.  This meant, as a practical matter, many waited years to raise the funds needed for hormone replacement therapy, other medicines, surgery, counseling, and so on. Far from idea.  One even sees “Go Fund Me” pages being set up by people to get the medical attention or coverage for which they have been denied, or for which the co pays and deductibles  are real hurdles.
Most insurance companies around the country, including health insurance companies, need to play by the rules set up by the state insurance commissioner or insurance oversight group in any state in  which they hope to sell and market insurance. Efforts have been made on a state-by-state basis with the insurance commissioners to help assure that the barriers to insured coverage are minimal.  It’s been a slog, but an example of what just happened in Wisconsin can be found here:  https://www.susans.org/2018/08/23/a-big-win-for-wisconsin-but-the-work-does-not-end-here/
At the federal level a part of the Affordable Care Act (Section 1557) has also been viewed as somewhat helpful in increasing coverage, as it outlaws gender discrimination and not just discrimination based on the more common categories.  See: https://www.hrc.org/blog/section-1557-of-the-affordable-care-act-and-what-it-means .
With a change in administrations, some see the current discussions about Section 1557, as a bit troubling–if the feds will not mandate that trans related care coverages exist in marketplace policies, what protections will there be for the community if they have an insurance company that prefers to say “no” rather than “yes” when treatment is sought?
Thus the value of individual state insurance commissioners taking on this issue. It is worth keeping up to date with your own state insurance commision office (or whatever it may be called in your state) as decisions there can affect you.
Two more possible articles of interest surrounding this topic and issue  incude https://www.cnn.com/2018/05/31/health/transgender-surgery-insurance/index.html and this piece from the TransEquallity group and their article on your healthcare rights:  https://transequality.org/know-your-rights/healthcare