Results of operations depend on our ability to manage expenses associated with health benefits (including estimated costs incurred) and selling, general and administrative (SG&A) costs. We measure operating performance based upon two key ratios. The health benefits ratio (HBR) represents medical costs as a percentage of premium revenues, excluding premium tax and health insurer fee revenues that are separately billed, and reflects the direct relationship between the premiums received and the medical services provided. The SG&A expense ratio represents SG&A costs as a percentage of premium and service revenues, excluding premium tax and health insurer fee revenues that are separately billed.
•Adjusted SG&A expense ratio of 8.9% for 2020, compared to 9.2% for 2019.
•Adjusted Diluted EPS of $5.00 for 2020, compared to $4.42 for 2019.
•We expect Medicaid eligibility redeterminations to begin on May 1, 2021, resulting in a decrease in membership.
Normal operations are funded primarily through operating cash flows and borrowings under our Revolving Credit Facility. In 2020, operating activities provided cash of $5.5 billion, or 3.1 times net earnings, compared to $1.5 billion in 2019. Cash flow provided by operations in 2020 was due to net earnings, an increase in medical claims liabilities from growth and expansions, and an increase in other long-term liabilities related to minimum MLR payables and a delay in employer payroll tax payments related to the COVID-19 extensions to payment deadlines.
In February 2020, we issued $2.0 billion 3.375% Senior Notes due 2030 (the $2.0 billion 2030 Notes). We used the net proceeds from the $2.0 billion 2030 Notes to redeem all of our outstanding 2024 Notes. We recognized a pre-tax loss on extinguishment of $44 million, including the call premium, the write-off of unamortized debt issuance costs and a loss on the termination of the $1.0 billion interest rate swap associated with the 2024 Notes. We intended to use remaining proceeds to redeem our 2022 Notes. The 2022 Notes were redeemed in the fourth quarter in connection with an additional offering of senior notes as further described below, and we decided to increase liquidity with the remaining proceeds of the $2.0 billion 2030 Notes.
In October 2020, we issued $2.2 billion 3.0% Senior Notes due October 2030 (the $2.2 billion 2030 Notes). We used the net proceeds from the offering, together with cash on hand, to redeem all of the 2022 Notes and the $1.2 billion 5.25% Senior Notes due 2025. We recognized a pre-tax loss on extinguishment of $17 million, including the call premium, and the write-off of unamortized debt issuance costs.
The indentures governing our various maturities of senior notes contain limited restrictive covenants. As of December 31, 2020, we were in compliance with all covenants.
The unaudited pro forma total revenues for the year ended December 31, 2020 was $112,905 million. It is impracticable for the Company to determine the pro forma earnings information for the year ended December 31, 2020 due to the nature of obtaining that information as the Company immediately began integrating WellCare into its ongoing operations.
The pro forma results do not reflect any anticipated synergies, efficiencies, or other cost savings of the acquisition. Accordingly, the unaudited pro forma financial information is not indicative of the results if the acquisition had been completed on January 1, 2019 and is not a projection of future results. The unaudited pro forma financial information does not reflect the previously discussed divestitures as the impact would be impracticable to quantify.
The Company's net receivables (payables) for each of the programs are as follows ($ in millions):
The Company's stock incentive plans allow for the granting of restricted stock or restricted stock unit awards and options to purchase common stock. Both incentive stock options and nonqualified stock options can be awarded under the plans. However, an immaterial amount of options were granted, exercised, or outstanding in 2020. The plans have 16 million shares available for future awards, however, 10 million shares relate to legacy WellCare shares and based on the terms of the WellCare acquisition, these shares are only available for awards to legacy WellCare employees and new Centene employees. Compensation expense for stock options and restricted stock unit awards is recognized on a straight-line basis over the vesting period, generally three to five years for stock options and one to three years for restricted stock or restricted stock unit awards. Vesting is accelerated by one year for individuals who qualify under the Company's retirement eligible provisions. Certain restricted stock unit awards contain performance-based as well as service-based provisions. Certain awards provide for accelerated vesting if there is a change in control as defined in the plans. The total compensation cost that has been charged against income for the stock incentive plans was $281 million, $177 million and $145 million for the years ended December 31, 2020, 2019 and 2018, respectively. The total income tax benefit recognized in the Statements of Operations for stock-based compensation arrangements was $34 million, $22 million and $34 million for the years ended December 31, 2020, 2019 and 2018, respectively.
Segment information for the year ended December 31, 2018, follows ($ in millions):