This takes a more restrictive view of medical billing and excludes said profits still:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4283267/"Conclusions:
A simplified financing system in the U.S. could result in cost savings exceeding $350 billion annually, nearly 15% of health care spending."
It also says "Morra and colleagues estimated annual BIR costs in physicians’ practices at $82,975 per physician in the U.S. versus $22,205 in Ontario, Canada [5], i.e., 73% lower."
PS: I would say 100% of the insurance industry excluding doctor payments is medical billing and "Insurance carriers and related activities contributed $450.3 billion, or 2.6 percent, of U.S. gross domestic product in 2014, according to the U.S. Bureau of Economic Analysis." http://www.iii.org/fact-statistic/industry-overview