I don't know about the military, but they are definitely a subsidiary of the AARP. I just had my "Medicare Advantage" plan with Regence dropped fpr 2014.
One of the choices in my area was United, but no way in hell would I ever support the damned AARP by giving them money.
Fortunately, Humana is also in my area, and both my primary care physician and my usual pharmacy are "in plan" with them.
No, UnitedHealthCare is its own company. They pay AARP a fee to provide insurance for them. This is how it works with insurance companies and AARP:
An insurance company makes a bid to provide health insurance to AARP members. Before UnitedHealthCare, we had a different insurance company. If another health insurance company makes a better bid for AARP members healthcare, UnitedHealthCare would be dropped and another company would get that contract.
An insurance company makes a bid to provide life insurance for AARP members. New York Life Insurance Co. has that contract. I have a life insurance policy with New York Life Insurance company through AARP.
Met Life provides long term care insurance for AARP members and I have that policy.
The Hartford Auto Insurance company provides auto insurance for AARP members. I don't have that policy but I should as it would be cheaper than the one I have.
So, AARP does not own any insurance company - they take the better bid from whichever company has the better bid for that particular kind of insurance.