GUARANTEES AND CONTINGENCIES	9 Months Ended
GUARANTEES AND CONTINGENCIES	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
GUARANTEES AND CONTINGENCIES	GUARANTEES AND CONTINGENCIES Government Contracts Our Medicare products, which accounted for approximately 78% of our total premiums and services revenue for the nine months ended September 30, 2017, primarily consisted of products covered under the Medicare Advantage and Medicare Part D Prescription Drug Plan contracts with the federal government. These contracts are renewed generally for a calendar year term unless CMS notifies us of its decision not to renew by May 1 of the calendar year in which the contract would end, or we notify CMS of our decision not to renew by the first Monday in June of the calendar year in which the contract would end. All material contracts between Humana and CMS relating to our Medicare products have been renewed for 2018, and all of our product offerings filed with CMS for 2018 have been approved. CMS uses a risk-adjustment model which adjusts premiums paid to Medicare Advantage, or MA, plans according to health status of covered members. The risk-adjustment model, which CMS implemented pursuant to the Balanced Budget Act of 1997 (BBA) and the Benefits Improvement and Protection Act of 2000 (BIPA), generally pays more where a plan's membership has higher expected costs. Under this model, rates paid to MA plans are based on actuarially determined bids, which include a process whereby our prospective payments are based on our estimated cost of providing standard Medicare-covered benefits to an enrollee with a "national average risk profile." That baseline payment amount is adjusted to reflect the health status of our enrolled membership. Under the risk-adjustment methodology, all MA plans must collect and submit the necessary diagnosis code information from hospital inpatient, hospital outpatient, and physician providers to CMS within prescribed deadlines. The CMS risk-adjustment model uses the diagnosis data to calculate the risk-adjusted premium payment to MA plans, which CMS adjusts for coding pattern differences between the health plans and the government fee-for-service program. We generally rely on providers, including certain providers in our network who are our employees, to code their claim submissions with appropriate diagnoses, which we send to CMS as the basis for our payment received from CMS under the actuarial risk-adjustment model. We also rely on these providers to document appropriately all medical data, including the diagnosis data submitted with claims. In addition, we conduct medical record reviews as part of our data and payment accuracy compliance efforts, to more accurately reflect diagnosis conditions under the risk adjustment model. These compliance efforts include the internal contract level audits described in more detail below. CMS is phasing-in the process of calculating risk scores using diagnoses data from the Risk Adjustment Processing System, or RAPS, to diagnoses data from the Encounter Data System, or EDS. The RAPS process requires MA plans to apply a filter logic based on CMS guidelines and only submit claims that satisfy those guidelines. For submissions through EDS, CMS requires MA plans to submit all the encounter data and CMS will apply the risk adjustment filtering logic to determine the risk scores. For 2016, 10% of the risk score was calculated from claims data submitted through EDS, increasing to 25% of the risk score calculated from claims data through EDS for 2017. In April 2017, CMS revised the pace of the phase-in. For 2018, 15% of the risk score will be calculated from claims data submitted through EDS. The phase-in from RAPS to EDS could result in different risk scores from each dataset as a result of plan processing issues, CMS processing issues, or filtering logic differences between RAPS and EDS, and could have a material adverse effect on our results of operations, financial position, or cash flows. CMS is continuing to perform audits of various companies’ selected MA contracts related to this risk adjustment diagnosis data. We refer to these audits as Risk-Adjustment Data Validation Audits, or RADV audits. RADV audits review medical records in an attempt to validate provider medical record documentation and coding practices which influence the calculation of premium payments to MA plans. In 2012, CMS released a “Notice of Final Payment Error Calculation Methodology for Part C Medicare Advantage Risk Adjustment Data Validation (RADV) Contract-Level Audits.” The payment error calculation methodology provides that, in calculating the economic impact of audit results for an MA contract, if any, the results of the RADV audit sample will be extrapolated to the entire MA contract after a comparison of the audit results to a similar audit of Medicare FFS (we refer to the process of accounting for errors in FFS claims as the "FFS Adjuster"). This comparison of RADV audit results to the FFS error rate is necessary to determine the economic impact, if any, of RADV audit results because the government used the Medicare FFS program data set, including any attendant errors that are present in that data set, to estimate the costs of various health status conditions and to set the resulting adjustments to MA plans’ payment rates. CMS already makes other adjustments to payment rates based on a comparison of coding pattern differences between MA plans and Medicare FFS data (such as for frequency of coding for certain diagnoses in MA plan data versus the Medicare FFS program dataset). The final RADV extrapolation methodology, including the first application of extrapolated audit results to determine audit settlements, is expected to be applied to RADV contract level audits conducted for contract year 2011 and subsequent years. CMS is currently conducting RADV contract level audits for contract years 2011, 2012, and 2013 in which two, five and five of our Medicare Advantage plans are being audited, respectively. Per CMS guidance, selected MA contracts will be notified of an audit at some point after the close of the final reconciliation for the payment year being audited. Estimated audit settlements are recorded as a reduction of premiums revenue in our consolidated statements of income, based upon available information. We perform internal contract level audits based on the RADV audit methodology prescribed by CMS. Included in these internal contract level audits is an audit of our Private Fee-For- Service business which we used to represent a proxy of the FFS Adjuster which has not yet been released. We based our accrual of estimated audit settlements for each contract year on the results of these internal contract level audits and update our estimates as each audit is completed. Estimates derived from these results were not material to our results of operations, financial position, or cash flows. We report the results of these internal contract level audits to CMS, including identified overpayments, if any. However, as indicated, we are awaiting additional guidance from CMS regarding the FFS Adjuster. Accordingly, we cannot determine whether such RADV audits will have a material adverse effect on our results of operations, financial position, or cash flows. In addition, CMS' comments in formalized guidance regarding “overpayments” to MA plans appear to be inconsistent with CMS' prior RADV audit guidance. These statements, contained in the preamble to CMS’ final rule release regarding Medicare Advantage and Part D prescription drug benefit program regulations for Contract Year 2015, appear to equate each Medicare Advantage risk adjustment data error with an “overpayment” without reconciliation to the principles underlying the FFS Adjuster referenced above. We will continue to work with CMS to ensure that MA plans are paid accurately and that payment model principles are in accordance with the requirements of the Social Security Act, which, if not implemented correctly could have a material adverse effect on our results of operations, financial position, or cash flows. At September 30, 2017, our military services business, which accounted for approximately 0.7% of our total premiums and services revenue for the nine months ended September 30, 2017, primarily consisted of the TRICARE South Region contract. The current 5-year South Region contract, which was set to expire on March 31, 2017, is subject to annual renewals on April 1 of each year during its term at the government’s option, including an option to extend for a sixth year through March 31, 2018. On March 2, 2017, we received notice that the Defense Health Agency, or DHA, had exercised its option to extend the TRICARE South Region contract for that sixth year. On July 21, 2016, we were notified by the DHA that we were awarded the contract for the new TRICARE East Region, which is a consolidation of the former North and South Regions, with delivery of health care services expected to commence on October 1, 2017. On March 30, 2017, we received notice that the DHA is moving the date upon which delivery of health care services is expected to commence under the new TRICARE East Region contract from October 1, 2017 to January 1, 2018. We expect the sixth option period under the current TRICARE South Region contract would be terminated in the event that delivery of health care services under the new TRICARE East Region contract commences prior to March 31, 2018. Our state-based Medicaid business accounted for approximately 5% of our total premiums and services revenue for the nine months ended September 30, 2017. In addition to our state-based Temporary Assistance for Needy Families, or TANF, Medicaid contracts in Florida and Kentucky, we have contracts in Florida for Long Term Support Services (LTSS), in Illinois and Virginia for stand-alone dual eligible demonstration programs serving individuals dually eligible for both the federal Medicare program and the applicable state-based Medicaid program, as well as an Integrated Care Program, or ICP, Medicaid contract in Illinois. Our Integrated Care Program Medicaid contract in Illinois, and the Virginia stand-alone dual eligible demonstration program both will terminate at December 31, 2017. The loss of any of the contracts above or significant changes in these programs as a result of legislative or regulatory action, including reductions in premium payments to us, regulatory restrictions on profitability, including by comparison of our Medicare Advantage profitability to our non-Medicare Advantage business profitability and a requirement that they remain within certain ranges of each other, or increases in member benefits without corresponding increases in premium payments to us, may have a material adverse effect on our results of operations, financial position, and cash flows. Legal Proceedings and Certain Regulatory Matters On January 6, 2012, the Civil Division of the United States Attorney’s Office for the Southern District of Florida advised us that it is seeking documents and information from us and several of our affiliates relating to several matters including the coding of medical claims by one or more South Florida medical providers, and loans to physician practices. On May 1, 2014, the U.S. Attorney's Office filed a Notice of Non-Intervention in connection with a civil qui tam suit related to one of these matters captioned United States of America ex rel. Olivia Graves v. Plaza Medical Centers, et al., and the Court ordered the complaint unsealed. Subsequently, the individual plaintiff amended the complaint and served the Company, opting to continue to pursue the action. As of November 7, 2017, all parties to the lawsuit and the United States have executed a settlement agreement to settle the plaintiff’s claims for damages and penalties, with Humana paying an amount that is not material to our results of operations. The parties are awaiting the court’s dismissal of the case. As previously disclosed, the Civil Division of the United States Department of Justice had provided us with an information request, separate from but related to the Plaza Medical matter, concerning our Medicare Part C risk adjustment practices. The request relates to our oversight and submission of risk adjustment data generated by providers in our Medicare Advantage network, including the providers identified in the Plaza Medical matter, as well as to our business and compliance practices related to risk adjustment data generated by our providers and by us, including medical record reviews conducted as part of our data and payment accuracy compliance efforts, the use of health and well-being assessments, and our fraud detection efforts. We believe that this request for information is in connection with a wider review of Medicare Risk Adjustment generally that includes a number of Medicare Advantage plans, providers and vendors. We continue to cooperate with and voluntarily respond to the information requests from the Department of Justice and the U.S. Attorney’s Office. These matters are expected to result in additional qui tam litigation. On January 19, 2016, an individual filed a qui tam suit captioned United States of America ex rel. Steven Scott v. Humana, Inc., in United States District Court, Central District of California, Western Division. The complaint alleges certain civil violations by us in connection with the actuarial equivalence of the plan benefits under Humana’s Basic PDP plan, a prescription drug plan offered by us under Medicare Part D, as compared to required benefit levels under applicable bid rules. The action seeks damages and penalties on behalf of the United States under the False Claims Act. The court ordered the qui tam action unsealed on September 13, 2017, so that the relator can proceed, following notice from the U.S. Government that it is not intervening at this time. We take seriously our obligations to comply with applicable CMS requirements and actuarial best principles, and we intend to vigorously defend against these allegations. On November 2, 2017, we filed suit against the United States of America in the United States Court of Federal Claims, on behalf of our health plans seeking recovery from the federal government of approximately $611 million in payments under the risk corridor premium stabilization program established under Health Care Reform, for years 2014, 2015 and 2016. We have not recognized revenue, nor have we recorded a receivable, for any amount due from the federal government for unpaid risk corridor payments as of September 30, 2017. We have fully recognized all liabilities due to the federal government that we have incurred under the risk corridor program, and have paid all amounts due to the federal government as required. There is no assurance that we will prevail in the lawsuit. Other Lawsuits and Regulatory Matters Our current and past business practices are subject to review or other investigations by various state insurance and health care regulatory authorities and other state and federal regulatory authorities. These authorities regularly scrutinize the business practices of health insurance, health care delivery and benefits companies. These reviews focus on numerous facets of our business, including claims payment practices, statutory capital requirements, provider contracting, risk adjustment, competitive practices, commission payments, privacy issues, utilization management practices, pharmacy benefits, access to care, and sales practices, among others. Some of these reviews have historically resulted in fines imposed on us and some have required changes to some of our practices. We continue to be subject to these reviews, which could result in additional fines or other sanctions being imposed on us or additional changes in some of our practices. We also are involved in various other lawsuits that arise, for the most part, in the ordinary course of our business operations, certain of which may be styled as class-action lawsuits. Among other matters, this litigation may include employment matters, claims of medical malpractice, bad faith, nonacceptance or termination of providers, anticompetitive practices, improper rate setting, provider contract rate and payment disputes, general contractual matters, intellectual property matters, and challenges to subrogation practices. For example, a number of hospitals and other providers have asserted that, under their network provider contracts, we are not entitled to reduce Medicare Advantage payments to these providers in connection with changes in Medicare payment systems and in accordance with the Balanced Budget and Emergency Deficit Control Act of 1985, as amended (commonly referred to as “sequestration”). Those challenges have led and could lead to arbitration demands or other litigation. Also, under state guaranty assessment laws, including those related to state cooperative failures in the industry, we may be assessed (up to prescribed limits) for certain obligations to the policyholders and claimants of insolvent insurance companies that write the same line or lines of business as we do. Penn Treaty is a financially distressed unaffiliated long-term care insurance company. On March 1, 2017, a court ordered the liquidation of Penn Treaty which triggered assessments from state guaranty associations that resulted in our recording a $54 million estimate in operating costs in the three months ended March 31, 2017. As a government contractor, we may also be subject to qui tam litigation brought by individuals who seek to sue on behalf of the government, alleging that the government contractor submitted false claims to the government including, among other allegations, those resulting from coding and review practices under the Medicare risk adjustment model. Qui tam litigation is filed under seal to allow the government an opportunity to investigate and to decide if it wishes to intervene and assume control of the litigation. If the government does not intervene, the lawsuit is unsealed, and the individual may continue to prosecute the action on his or her own, on behalf of the government. We also are subject to other allegations of non-performance of contractual obligations to providers, members, and others, including failure to properly pay claims, improper policy terminations, challenges to our implementation of the Medicare Part D prescription drug program and other litigation. A limited number of the claims asserted against us are subject to insurance coverage. Personal injury claims, claims for extra contractual damages, care delivery malpractice, and claims arising from medical benefit denials are covered by insurance from our wholly owned captive insurance subsidiary and excess carriers, except to the extent that claimants seek punitive damages, which may not be covered by insurance in certain states in which insurance coverage for punitive damages is not permitted. In addition, insurance coverage for all or certain forms of liability has become increasingly costly and may become unavailable or prohibitively expensive in the future. We record accruals for the contingencies discussed in the sections above to the extent that we conclude it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. No estimate of the possible loss or range of loss in excess of amounts accrued, if any, can be made at this time regarding the matters specifically described above because of the inherently unpredictable nature of legal proceedings, which also may be exacerbated by various factors, including: (i) the damages sought in the proceedings are unsubstantiated or indeterminate; (ii) discovery is not complete; (iii) the proceeding is in its early stages; (iv) the matters present legal uncertainties; (v) there are significant facts in dispute; (vi) there are a large number of parties (including where it is uncertain how liability, if any, will be shared among multiple defendants); or (vii) there is a wide range of potential outcomes. The outcome of any current or future litigation or governmental or internal investigations, including the matters described above, cannot be accurately predicted, nor can we predict any resulting judgments, penalties, fines or other sanctions that may be imposed at the discretion of federal or state regulatory authorities or as a result of actions by third parties. Nevertheless, it is reasonably possible that any such outcome of litigation, judgments, penalties, fines or other sanctions could be substantial, and the outcome of these matters may have a material adverse effect on our results of operations, financial position, and cash flows, and may also affect our reputation.