The GAO used enrollment data from 2015-17 that health insurers reported to CMS and compared the data to 2011-14 enrollment figures. Some data sets also included other state and federal numbers.
The health insurers with the largest share in each state and the District of Columbia’s large group market in 2016:
Alabama — Blue Cross and Blue Shield of Alabama (92.9 percent)
Alaska — Premera Blue Cross (83.9 percent)
Arizona — Blue Cross and Blue Shield of Arizona (38.4 percent)
Arkansas — Arkansas Blue Cross and Blue Shield (78.5 percent)
California — Kaiser Foundation (47.9 percent)
Colorado — Kaiser Foundation (48.5 percent)
Connecticut — WellPoint (29.8 percent)
Delaware — Highmark (69.8 percent)
District of Columbia — Aetna (37.4 percent)
Florida — Blue Cross and Blue Shield of Florida (49.4 percent)
Georgia — WellPoint (44.1 percent)
Hawaii — Hawaii Medical Service Association (68.9 percent)
Idaho — Blue Cross of Idaho Health Service (65.5 percent)
Illinois — Health Care Service Corp. (66.4 percent)
Indiana — WellPoint (61.5 percent)
Iowa — Wellmark (77.7 percent)
Kansas — Blue Cross and Blue Shield of Kansas (51.6 percent)
Kentucky — WellPoint (67.4 percent)
Louisiana — Blue Cross and Blue Shield of Louisiana (65 percent)
Maine — WellPoint (70.3 percent)
Maryland — CareFirst (65.5 percent)
Massachusetts — Blue Cross Blue Shield of Massachusetts (58.1 percent)
Michigan — Blue Cross Blue Shield of Michigan (54.9 percent)
Minnesota — HealthPartners (45.8 percent)
Mississippi — Mississippi Insurance Group (82.4 percent)
Missouri — Blue Cross and Blue Shield of Kansas City (29.2 percent)
Montana — Health Care Service Corp. (83.4 percent)
Nebraska — Blue Cross and Blue Shield of Nebraska (77.1 percent)
Nevada — UnitedHealth Group (65.4 percent)
New Hampshire — WellPoint (57.0 percent)
New Jersey — Horizon Blue Cross Blue Shield of New Jersey (54.1 percent)
New Mexico — Health Care Service Corp. (61.8 percent)
New York — Lifetime Healthcare (17.3 percent)
North Carolina — Blue Cross and Blue Shield of North Carolina (68.7 percent)
North Dakota — Noridian Mutual Insurance Company (49.7 percent)
Ohio — WellPoint (44.3 percent)
Oklahoma — Health Care Service Corp. (52.5 percent)
Oregon — Kaiser Foundation (41.9 percent)
Pennsylvania — Highmark (35.1 percent)
Rhode Island — Blue Cross & Blue Shield of Rhode Island (78.0 percent)
South Carolina — BlueCross BlueShield of South Carolina (88.6 percent)
South Dakota — Wellmark (55.1 percent)
Tennessee — BlueCross BlueShield of Tennessee (72.5 percent)
Texas — Health Care Service Corp. (45.9 percent)
Utah — IHC Group (42.1 percent)
Vermont — Blue Cross Blue Shield of Vermont (88.7 percent)
Virginia — WellPoint (48.3 percent)
Washington — Group Health Cooperative (32.6 percent)
West Virginia — Highmark (78.3 percent)
Wisconsin — WellPoint (15.2 percent)
Wyoming — Blue Cross Blue Shield of Wyoming (74.4 percent)
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