Virtually all major insurance companies recognize that transgender-related medical care is medically necessary and have a written policy describing their criteria for when plans they administer will cover it. Medical policies have many names including Medical Coverage Policy, Clinical Policy Bulletin, UM Guideline, or Clinical Criteria.
You must look to your individual plan to determine if transgender care is covered or excluded. Only if it is covered will the policy apply. You can learn more about finding your plan's clinical criteria here. You can also download instructions for finding your clinical criteria here.
The Trans Health Project historically compiled information on medical policies for major insurers. Below is an archive of past medical policies compiled by the Trans Health Project; the fact that an insurance company is listed below does not mean that your particular plan will follow these guidelines. Please see the time stamp at the bottom of each page to see when the information was last updated.