Total revenues increased 8.8% in the three months ended September 30, 2020 compared to the prior year primarily driven by membership growth in the Health Care Benefits segment’s Government products and the favorable impact of the reinstatement of the HIF for 2020. These increases were partially offset by the divestitures of Aetna’s standalone Medicare Part D prescription drug plans (which the Company retained the financial results of through 2019) and Workers Compensation business, membership declines in the segment’s Commercial products and planned COVID-19 related investments benefiting customers and members in the three months ended September 30, 2020.
Operating income and adjusted operating income decreased 8.4% and 24.1%, respectively, in the three months ended September 30, 2020, compared to the prior year. The decrease in both operating income and adjusted operating income was primarily driven by the planned COVID-19 related investments described above and the divestitures of Aetna’s standalone Medicare Part D prescription drug plans (“PDPs”) and Workers’ Compensation business. The decrease in operating income was partially offset by the $271 million pre-tax gain on the sale of the Workers’ Compensation business.
The Health Care Benefits segment’s MBR increased 70 basis points in the three months ended September 30, 2020 compared to the prior year primarily driven by the planned COVID-19 related investments described above, shifts in business mix and the divestiture of Aetna’s standalone PDPs, partially offset by the reinstatement of the HIF for 2020.
Medical membership as of September 30, 2020 of 23.3 million decreased 316 thousand members compared with June 30, 2020, primarily reflecting a decline in Commercial products, partially offset by increases in Medicaid and Medicare products.
The Health Care Benefits segment experienced favorable development of prior-periods’ health care cost estimates during the three months ended September 30, 2020 driven by favorable development in its Government businesses, primarily attributable to second quarter 2020 performance, and development in its Commercial business largely in-line with its reserve estimated at June 30, 2020.
Prior years’ health care costs payable estimates developed favorably by $448 million during the nine months ended September 30, 2020. This development is reported on a basis consistent with the prior years’ development reported in the health care costs payable table in the Company’s annual audited financial statements and does not directly correspond to an increase in 2020 operating results.