CIGNA Corporation (NYSE:CI) is a health insurance company - sort of. For one, three-quarters of Cigna's health insurance business isn't really insurance - Cigna manages health plans for companies who self-insure, agreeing to pay employee's health care costs. Employees get Cigna cards and access to Cigna's negotiated rates with doctors, and Cigna handles billing, but the employer bears the risk of paying for care when employees get sick. This arrangement means less risk for Cigna, but also smaller premiums. The majority of CIGNA's revenues come from these so called self-funded administrative-only plans.
Cigna also differs from its competitors in that the majority of the company's pretax operating income comes from investment income- 50% higher than its next most-invested competitor, Aetna, and almost four times that of other large national health account providers.  This reliance on investment income makes the company much more vulnerable to market conditions than most other health insurance companies.(Read more at Wikinvest )