Our industry relies on two key statistics to measure performance. The benefit ratio, which is computed by taking total benefits expense as a percentage of premiums revenue, represents a statistic used to measure underwriting profitability. The operating cost ratio, which is computed by taking total operating costs, excluding depreciation and amortization, as a percentage of total revenue less investment income, represents a statistic used to measure administrative spending efficiency.
The results of each segment are measured by income before income taxes. Transactions between reportable segments primarily consist of sales of services rendered by our Healthcare Services segment, primarily pharmacy, provider, and home based services as well as clinical programs, to our Retail and Group customers. Intersegment sales and expenses are recorded at fair value and eliminated in consolidation. Members served by our segments often use the same provider networks, enabling us in some instances to obtain more favorable contract terms with providers. Our segments also share indirect costs and assets. As a result, the profitability of each segment is interdependent. We allocate most operating expenses to our segments. Assets and certain corporate income and expenses are not allocated to the segments, including the portion of investment income not supporting segment operations, interest expense on corporate debt, and certain other corporate expenses. These items are managed at a corporate level. These corporate amounts are reported separately from our reportable segments and are included with intersegment eliminations.
On February 14, 2017, we and Aetna agreed to mutually terminate the Merger Agreement. We also announced that the Board had approved a new authorization for share repurchases of up to $2.25 billion of our common stock exclusive of shares repurchased in connection with employee stock plans, expiring on December 31, 2017. Under this new authorization, we expect to complete a $1.5 billion accelerated share repurchase program in the first quarter of 2017. Under terms of the Merger Agreement, we are entitled to a breakup fee of $1 billion.
Our Healthcare Effectiveness Data and Information Set, or HEDIS, measures, demonstrating the achievement of clinical outcomes, are at record-high results for the company. Accordingly, we believe that our Star ratings for the 2018 bonus year do not accurately reflect our actual performance under certain Star measures. Consequently, we filed for reconsideration of certain of those ratings under the appropriate administrative process. We are also evaluating our contract structures for rationalization to mitigate the negative impact on Star bonus revenues for 2018.
For full year 2017, we expect net membership growth in our Group Medicare Advantage offerings of 70,000 to 80,000.
As discussed in the detailed Healthcare Services segment results of operations discussion that follows, our Healthcare Services segment pretax income increased $86 million, or 8.8%, for the year ended December 31, 2016. This increase was primarily due to incremental earnings associated with revenue growth from our pharmacy solutions business as it increased mail-order penetration and served our growing individual Medicare membership, partially offset by ongoing pressures in our provider services business reflecting significantly lower Medicare rates year-over-year associated with CMS' risk coding recalibration for 2016 in geographies where our provider assets are primarily located.
The Health Care Reform Law enacted significant reforms to various aspects of the U.S. health insurance industry. Certain significant provisions of the Health Care Reform Law include, among others, mandated coverage requirements, mandated benefits and guarantee issuance associated with commercial medical insurance, rebates to policyholders based on minimum benefit ratios, adjustments to Medicare Advantage premiums, the establishment of federally-facilitated or state-based exchanges coupled with programs designed to spread risk among insurers, and the introduction of plan designs based on set actuarial values. In addition, the Health Care Reform Law established insurance industry assessments, including an annual health insurance industry fee and a three-year $25 billion industry wide commercial reinsurance fee. The annual health insurance industry fee levied on the insurance industry was $8 billion in 2014 and $11.3 billion in each of 2015 and 2016, with increasing annual amounts starting in 2018, and is not deductible for income tax purposes, which significantly increased our effective income tax rate. Our effective tax rate for 2016 was approximately 60.5%. The Consolidated Appropriations Act, 2016, enacted on December 18, 2015, included a one-time one year suspension in 2017 of the health insurer fee. This suspension will significantly reduce our operating costs and effective tax rate in 2017. Our effective tax rate for 2017 is expected to be approximately 36% to 37%. The decline in the effective tax rate primarily is due to the suspension of the annual health insurance industry fee in 2017. The health insurance industry fee levied on the insurance industry was previously expected to be $14 billion in 2017. In 2016, we paid the federal government $916 million for the annual health insurance industry fee, a 5.7% increase from $867 million in 2015, primarily reflecting growth in our market share.
Group Medicare Advantage membership decreased 128,700 members, or 26.6%, from December 31, 2015 to December 31, 2016 reflecting the loss of a large account that moved to a private exchange offering on January 1, 2016.
Individual specialty membership decreased 65,000 members, or 5.6%, from December 31, 2015 to December 31, 2016 primarily due to the loss of individual commercial medical members that also had specialty coverage.
The Retail segment benefit ratio of 86.2% for 2016 decreased 50 basis points from 2015 primarily due to lower year-over-year Medicare Advantage utilization, favorable comparisons of prior-year medical claims reserve development, and the impact of the premium deficiency reserve recorded in the fourth quarter of 2015 for certain of our individual commercial medical products for the 2016 coverage year. These items were partially offset by the reduction of premiums related to the write-off of receivables associated with the commercial risk corridor premium stabilization program which increased the Retail segment benefit ratio by approximately 100 basis points in 2016. As previously disclosed, in the fourth quarter of 2015 we recorded a premium deficiency reserve associated with our 2016 individual commercial offerings compliant with the Health Care Reform Law, increasing our 2015 benefit ratio by 40 basis points. During 2016, we increased the premium deficiency reserve for the 2016 coverage year and recorded a change in estimate of $208 million with a corresponding increase in benefits expense primarily as a result of unfavorable current and projected claims experience.
The Retail segment operating cost ratio of 11.5% for 2016 increased 30 basis points from 2015 primarily due to the impact on premiums of the write-off of receivables associated with the commercial risk corridor premium stabilization program, the unfavorable comparison to unusually low operating expenses in 2015 resulting from the temporary suspension of certain discretionary administrative costs, and the loss of a large group Medicare Advantage account which carried a lower operating cost ratio than that for our individual Medicare Advantage business. The non-deductible health insurance industry fee increased the operating cost ratio by approximately 170 basis points in 2016 as compared to 160 basis points in 2015.
Investment income totaled $474 million for 2015, an increase of $97 million from 2014, primarily due to higher realized capital gains in 2015 as a result of the repositioning of our portfolio given recent market volatility and anticipated changes to interest rates, with higher average invested balances being substantially offset by lower interest rates.
Our effective tax rate during 2015 was 47.5% compared to the effective tax rate of 47.2% in 2014. The increase in the effective tax rate primarily was due to an increase in the non-deductible health insurance industry fee from 2014, substantially offset by the favorable tax effect of the gain on the sale of Concentra. See Note 11 to the consolidated financial statements included in Item 8. - Financial Statements and Supplementary Data for a complete reconciliation of the federal statutory rate to the effective tax rate.
We repurchased 1.85 million shares for $329 million in 2015 and 5.7 million shares for $730 million in 2014(excludes another $100 million held back pending final settlement of an accelerated stock repurchase plan in March 2015) under share repurchase plans authorized by the Board of Directors. We did not repurchase shares in 2016 due to restrictions under the Merger Agreement. We also acquired common shares in connection with employee stock plans for an aggregate cost of $104 million in 2016, $56 million in 2015, and $42 million in 2014.
We continually adjust our historical trend and completion factor experience with our knowledge of recent events that may impact current trends and completion factors when establishing our reserves. Because our reserving practice is to consistently recognize the actuarial best point estimate using an assumption of moderately adverse conditions as required by actuarial standards, there is a reasonable possibility that variances between actual trend and completion factors and those assumed in our December 31, 2016 estimates would fall towards the middle of the ranges previously presented in our sensitivity table.
We cover prescription drug benefits in accordance with Medicare Part D under multiple contracts with CMS. The payments we receive monthly from CMS and members, which are determined from our annual bid, represent amounts for providing prescription drug insurance coverage. We recognize premiums revenue for providing this insurance coverage ratably over the term of our annual contract. Our CMS payment is subject to risk sharing through the Medicare Part D risk corridor provisions. In addition, receipts for reinsurance and low-income cost subsidies as well as receipts for certain discounts on brand name prescription drugs in the coverage gap represent payments for prescription drug costs for which we are not at risk.
Operating results for our individual commercial medical business compliant with the Health Care Reform Law have been challenged primarily due to unanticipated modifications in the program subsequent to the passing of the Health Care Reform Law, resulting in higher covered population morbidity and the ensuing enrollment and claims issues causing volatility in claims experience. We took a number of actions in 2015 that we believed would improve the profitability of our individual commercial medical business in 2016. These actions were subject to regulatory restrictions in certain geographies and included premium increases for the 2016 coverage year related generally to the first half of 2015 claims experience, the discontinuation of certain products as well as exit of certain markets for 2016, network improvements, enhancements to claims and clinical processes and administrative cost control. Despite these actions, the deterioration in the second half of 2015 claims experience together with 2016 open enrollment results that included the retention of many high-utilizing members for 2016 resulted in a probable future loss. As a result of our assessment in the fourth quarter of 2015 of the profitability of our individual commercial medical policies compliant with the Health Care Reform Law, we recorded in that quarter a provision for probable future losses (premium deficiency reserve) for the 2016 coverage year of $176 million in benefits payable in our consolidated balance sheet with a corresponding increase in benefits expense in our consolidated statement of income. As noted in the table below, in the second quarter of 2016, we increased the premium deficiency reserve for the 2016 coverage year and recorded a change in estimate of $208 million with a corresponding increase in benefits expense in our condensed consolidated statement of income primarily as a result of currently and projected unfavorable claims experience.
Healthcare Services segment goodwill of $480 million associated with the sale of Concentra was included with assets-held-for sale as of January 1, 2015 and is excluded from the table above. This $480 million of goodwill was disposed of on June 1, 2015 with the completion of the sale of Concentra.
The following discussion provides information about incurred and paid claims development for our Retail and Group segments as of December 31, 2016, net of reinsurance, as well as cumulative claim frequency and the total of IBNR included within the net incurred claims amounts. The information about incurred and paid claims development for the years ended December 31, 2014 and 2015 is presented as supplementary information.
We have plans under which options to purchase our common stock and restricted stock units have been granted to executive officers, directors and key employees. For awards granted prior to July 2, 2015, our equity award agreements generally contain provisions whereby the awards automatically accelerate and vest upon change in control, including those granted to retirement-eligible participants described below. Awards granted on or after July 2, 2015 would generally require both a change in control and termination of employment within 2 years of the date of the change in control to accelerate the vesting, including those granted to retirement-eligible participants.
In connection with the Merger, three putative class action complaints were filed by purported Humana stockholders challenging the Merger, two in the Circuit Court of Jefferson County, Kentucky and one in the Court of Chancery of the State of Delaware. The complaints are captioned Solak v. Broussard et al., Civ. Act. No. 15CI03374 (Kentucky
segment consists of employer group commercial fully-insured medical and specialty health insurance benefits, including dental, vision, and other supplemental health and voluntary insurance benefits, as well as administrative services only, or ASO products. In addition, our Group segment includes our health and wellness products (primarily marketed to employer groups) and military services business, primarily our TRICARE South Region contract. The Healthcare Services segment includes services offered to our health plan members as well as to third parties, including pharmacy solutions, provider services, home based services, and clinical programs, as well as services and capabilities to advance population health. We will continue to report under the category of Other Businesses those businesses which do not align with the reportable segments described above, primarily our closed-block long-term care insurance policies.
Reinsurance recoverables represent the portion of future policy benefits payable and benefits payable that are covered by reinsurance. Amounts recoverable from reinsurers are estimated in a manner consistent with the methods used to determine future policy benefits payable as detailed in Note 2. Excluding reinsurance associated with the Health Care Reform Law discussed in Note 2, reinsurance recoverables, included in other current and long-term assets, were $822 million at December 31, 2016 and $668 million at December 31, 2015. The percentage of these reinsurance recoverables resulting from 100% coinsurance agreements was approximately 34% at December 31, 2016 and approximately 43% at December 31, 2015. Premiums ceded were $842 million in 2016, $821 million in 2015 and $357
We evaluate the financial condition of these reinsurers on a regular basis. These reinsurers are well-known and well-established, as evidenced by the strong financial ratings at December 31, 2016 presented below:
Total revenue for 2016 includes a reduction of $583 million ($367 million after-tax, or $2.43 per diluted common share) in premiums associated with the write-off of risk corridor receivables.