Basis Of Presentation and Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
Accounting Policies [Abstract]
Basis of Presentation and Significant Accounting Policies	Basis of Presentation and Significant Accounting Policies Basis of Presentation: The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. generally accepted accounting principles, or GAAP, for interim financial reporting. Accordingly, they do not include all of the information and footnotes required by GAAP for annual financial statements. We have omitted certain footnote disclosures that would substantially duplicate the disclosures in our 2019 Annual Report on Form 10-K, unless the information contained in those disclosures materially changed or is required by GAAP. Certain prior year amounts have been reclassified to conform to the current year presentation. For additional information on prior year reclassifications, see Note 15, “Segment Information.” In the opinion of management, all adjustments, including normal recurring adjustments, necessary for a fair statement of the consolidated financial statements as of and for the three and six months ended June 30, 2020 and 2019 have been recorded. The results of operations for the three and six months ended June 30, 2020 are not necessarily indicative of the results that may be expected for the full year ending December 31, 2020, or any other period. These unaudited consolidated financial statements should be read in conjunction with our audited consolidated financial statements as of and for the year ended December 31, 2019 included in our 2019 Annual Report on Form 10-K. Certain of our subsidiaries operate outside of the United States and have functional currencies other than the U.S. dollar, or USD. We translate the assets and liabilities of those subsidiaries to USD using the exchange rate in effect at the end of the period. We translate the revenues and expenses of those subsidiaries to USD using the average exchange rates in effect during the period. The net effect of these translation adjustments is included in “Foreign currency translation adjustments” in our consolidated statements of comprehensive income. Cash and Cash Equivalents: We control a number of bank accounts that are used exclusively to hold customer funds for the administration of customer benefits, and we have cash and cash equivalents on deposit to meet certain regulatory requirements. These amounts totaled $231 and $215 at June 30, 2020 and December 31, 2019, respectively, and are included in the cash and cash equivalents line on our consolidated balance sheets. Investments: Prior to 2020, our fixed maturities were evaluated for other-than-temporary impairment where credit-related impairments were presented within the other-than-temporary impairment losses recognized in our consolidated statements of income with an adjustment to the security’s amortized cost basis. Effective January 1, 2020, if a fixed maturity security is in an unrealized loss position and we have the intent to sell the fixed maturity security, or it is more likely than not that we will have to sell the fixed maturity security before recovery of its amortized cost basis, we write down the fixed maturity security’s cost basis to fair value and record an impairment loss in our consolidated statements of income. For impaired fixed maturity securities that we do not intend to sell or if it is more likely than not that we will not have to sell such securities, but we expect that we will not fully recover the amortized cost basis, we recognize the credit component of the impairment as an allowance for credit loss in our consolidated balance sheets and record an impairment loss in our consolidated statements of income. The non-credit component of the impairment is recognized in accumulated other comprehensive loss. Furthermore, unrealized losses entirely caused by non-credit-related factors related to fixed maturity securities for which we expect to fully recover the amortized cost basis continue to be recognized in accumulated other comprehensive loss. The credit component of an impairment is determined primarily by comparing the net present value of projected future cash flows with the amortized cost basis of the fixed maturity security. The net present value is calculated by discounting our best estimate of projected future cash flows at the effective interest rate implicit in the fixed maturity security at the date of purchase. For mortgage-backed and asset-backed securities, cash flow estimates are based on assumptions regarding the underlying collateral, including prepayment speeds, vintage, type of underlying asset, geographic concentrations, default rates, recoveries and changes in value. For all other securities, cash flow estimates are driven by assumptions regarding probability of default, including changes in credit ratings and estimates regarding timing and amount of recoveries associated with a default. For asset-backed securities included in fixed maturity securities, we recognize income using an effective yield based on anticipated prepayments and the estimated economic life of the securities. When estimates of prepayments change, the effective yield is recalculated to reflect actual payments to date and anticipated future payments. The net investment in the securities is adjusted to the amount that would have existed had the new effective yield been applied since the purchase date of the securities. Such adjustments are reported within net investment income. In accordance with the Financial Accounting Standards Board, or FASB, guidance, the changes in fair value of our marketable equity securities are recognized in our results of operations within net realized gains and losses on financial instruments. We have corporate-owned life insurance policies on certain participants in our deferred compensation plans and other members of management. The cash surrender value of the corporate-owned life insurance policies is reported under the caption “Other invested assets” in our consolidated balance sheets. We use the equity method of accounting for investments in companies in which our ownership interest may enable us to influence the operating or financial decisions of the investee company. Our proportionate share of equity in net income of these unconsolidated affiliates is reported within net investment income. The equity method investments are reported under the caption “Other invested assets” in our consolidated balance sheets. Investment income is recorded when earned. All securities sold resulting in investment gains and losses are recorded on the trade date. Realized gains and losses are determined on the basis of the cost or amortized cost of the specific securities sold. We participate in securities lending programs whereby marketable securities in our investment portfolio are transferred to independent brokers or dealers in exchange for cash and securities collateral. Under FASB guidance related to accounting for transfers and servicing of financial assets and extinguishments of liabilities, we recognize the collateral as an asset, which is reported under the caption “Other current assets” in our consolidated balance sheets, and we record a corresponding liability for the obligation to return the collateral to the borrower, which is reported under the caption “Other current liabilities” in our consolidated balance sheets. The securities on loan are reported in the applicable investment category on our consolidated balance sheets. Unrealized gains or losses on securities lending collateral are included in accumulated other comprehensive loss as a separate component of shareholders’ equity. The market value of loaned securities and that of the collateral pledged can fluctuate in non-synchronized fashions. To the extent the loaned securities’ value appreciates faster or depreciates slower than the value of the collateral pledged, we are exposed to the risk of the shortfall. As a primary mitigating mechanism, the loaned securities and collateral pledged are marked to market on a daily basis and the shortfall, if any, is collected accordingly. Secondarily, the collateral level is set at 102% of the value of the loaned securities, which provides a cushion before any shortfall arises. The investment of the cash collateral is subject to market risk, which is managed by limiting the investments to higher quality and shorter duration instruments. Receivables: Premium receivables include the uncollected amounts from insured groups, individuals and government programs. Premium receivables are reported net of an allowance for doubtful accounts of $259 and $237 at June 30, 2020 and December 31, 2019, respectively. Self-funded receivables include administrative fees, claims and other amounts due from self-funded customers. Self-funded receivables are reported net of an allowance for doubtful accounts of $52 and $46 at June 30, 2020 and December 31, 2019, respectively. The allowance for doubtful accounts is based on historical collection trends, future forecasts and our judgment regarding the ability to collect specific accounts. Other receivables include pharmacy rebates, provider advances, claims recoveries, reinsurance receivables, proceeds due from brokers on investment trades, other government receivables and other miscellaneous amounts due to us. These receivables are reported net of an allowance for doubtful accounts of $321 and $242 at June 30, 2020 and December 31, 2019, respectively, which is based on historical collection trends, future forecasts and our judgment regarding the ability to collect specific accounts. Revenue Recognition: For our non-fully-insured contracts, we had no material contract assets, contract liabilities or deferred contract costs recorded on our consolidated balance sheet at June 30, 2020. For the three and six months ended June 30, 2020, revenue recognized from performance obligations related to prior periods, such as due to changes in transaction price, was not material. For contracts that have an original expected duration of greater than one year, revenue expected to be recognized in future periods related to unfulfilled contractual performance obligations and contracts with variable consideration related to undelivered performance obligations is not material. Recently Adopted Accounting Guidance: In November 2019, the FASB issued Accounting Standards Update No. 2019-11, Codification Improvements to Topic 326, Financial Instruments - Credit Losses. In May 2019, the FASB issued Accounting Standards Update No. 2019-05, Financial Instruments - Credit Losses (Topic 326): Targeted Transition Relief. In April 2019, the FASB issued Accounting Standards Update No. 2019-04, Codification Improvements to Topic 326, Financial Instruments - Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments. In November 2018, the FASB issued Accounting Standards Update No. 2018-19, Codification Improvements to Topic 326, Financial Instruments - Credit Losses. These updates provide an option to irrevocably elect to measure certain individual financial assets at fair value instead of amortized cost and provide additional clarification and implementation guidance on certain aspects of the previously issued Accounting Standards Update No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, or ASU 2016-13, and have the same effective date and transition requirements as ASU 2016-13. ASU 2016-13 introduces a current expected credit loss model for measuring expected credit losses for certain types of financial instruments held at the reporting date based on historical experience, current conditions and reasonable supportable forecasts. ASU 2016-13 replaces the current incurred loss model for measuring expected credit losses, requires expected losses on available-for-sale debt securities to be recognized through an allowance for credit losses rather than as reductions in the amortized cost of the securities and provides for additional disclosure requirements. ASU 2016-13 requires a cumulative-effect adjustment to the opening balance of retained earnings on the statement of financial position at the date of adoption and a prospective transition approach for debt securities for which an other-than-temporary impairment had been recognized before the adoption date. The effect of a prospective transition approach is to maintain the same amortized cost basis before and after the date of adoption. We adopted ASU 2016-13 on January 1, 2020, and recognized a cumulative-effect adjustment of $35 to our opening retained earnings for credit related allowances on receivables. The adoption did not have an impact on our consolidated statements of income or cash flows. In August 2018, the FASB issued Accounting Standards Update No. 2018-15, Intangibles—Goodwill and Other—Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement that is a Service Contract, or ASU 2018-15. The amendments in ASU 2018-15 require implementation costs incurred by customers in cloud computing arrangements to be deferred and recognized over the term of the arrangement, if those costs would be capitalized by the customer in a software licensing arrangement under the internal-use software guidance. The amendments also require an entity to disclose the nature of its hosting arrangements and adhere to certain presentation requirements in its balance sheet, income statement and statement of cash flows. We adopted ASU 2018-15 on January 1, 2020 using a prospective approach for all implementation costs incurred after the date of adoption, and the adoption did not have an impact on our consolidated financial position, results of operations or cash flows. In August 2018, the FASB issued Accounting Standards Update No. 2018-13, Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, or ASU 2018-13. The amendments in ASU 2018-13 eliminate, add, and modify certain disclosure requirements for fair value measurements. The amendments are effective for interim and annual periods beginning after December 15, 2019, with early adoption permitted for either the entirety of ASU 2018-13 or only the provisions that eliminate or modify disclosure requirements. We early adopted the provisions that eliminate and modify disclosure requirements, on a retrospective basis, effective in our 2018 Annual Report on Form 10-K. We adopted the new disclosure requirements on January 1, 2020, on a prospective basis. In January 2017, the FASB issued Accounting Standards Update No. 2017-04, Intangibles - Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment, or ASU 2017-04. This update removes Step 2 of the goodwill impairment test under current guidance, which required a hypothetical purchase price allocation. The new guidance requires an impairment charge to be recognized for the amount by which the carrying amount exceeds the reporting unit’s fair value. We adopted ASU 2017-04 on January 1, 2020, and the adoption did not have an impact on our consolidated financial position, results of operations or cash flows. Recent Accounting Guidance Not Yet Adopted: In March 2020, the FASB issued Accounting Standards Update No. 2020-04, Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting, or ASU 2020-04. ASU 2020-04 provides optional expedients and exceptions for applying GAAP to contract modifications and hedging relationships, subject to meeting certain criteria, that reference the London Interbank Offered Rate, or LIBOR, or another reference rate expected to be discontinued because of the reference rate reform. The provisions must be applied at a Topic, Subtopic, or Industry Subtopic level for all transactions other than derivatives, which may be applied at a hedging relationship level. The provisions within ASU 2020-04 are available until December 31, 2022, when the reference rate replacement activity is expected to have been completed. We are currently evaluating the provisions within ASU 2020-04. In December 2019, the FASB issued Accounting Standards Update No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes, or ASU 2019-12. The amendments in ASU 2019-12 remove certain exceptions to the general principles in Accounting Standards Codification Topic 740. The amendments also clarify and amend existing guidance to improve consistent application. The amendments are effective for our annual reporting periods beginning after December 15, 2020, with early adoption permitted. The transition method (retrospective, modified retrospective, or prospective basis) related to the amendments depends on the applicable guidance, and all amendments for which there is no transition guidance specified are to be applied on a prospective basis. We are currently evaluating the effects the adoption of ASU 2019-12 will have on our consolidated financial statements. In August 2018, the FASB issued Accounting Standards Update No. 2018-14, Compensation—Retirement Benefits - Defined Benefit Plans—General (Subtopic 715-20): Disclosure Framework—Changes to the Disclosure Requirements for Defined Benefit Plans, or ASU 2018-14. The amendments in ASU 2018-14 eliminate, add, and modify certain disclosure requirements for employers that sponsor defined benefit pension or other postretirement plans. The amendments are effective for our annual reporting periods beginning after December 15, 2020, with early adoption permitted. The guidance is to be applied on a retrospective basis to all periods presented. We are currently evaluating the effects the adoption of ASU 2018-14 will have on our disclosures. In August 2018, the FASB issued Accounting Standards Update No. 2018-12, Financial Services—Insurance (Topic 944): Targeted Improvements to the Accounting for Long-Duration Contracts, or ASU 2018-12. The amendments in ASU 2018-12 make changes to a variety of areas to simplify or improve the existing recognition, measurement, presentation and disclosure requirements for long-duration contracts issued by an insurance entity. The amendments require insurers to annually review the assumptions they make about their policyholders and update the liabilities for future policy benefits if the assumptions change. The amendments also simplify the amortization of deferred contract acquisition costs and add new disclosure requirements about the assumptions insurers use to measure their liabilities and how they may affect future cash flows. The amendments in ASU 2018-12 will be effective for our interim and annual reporting periods beginning after December 15, 2021. The amendments related to the liability for future policy benefits for traditional and limited-payment contracts and deferred acquisition costs are to be applied to contracts in force as of the beginning of the earliest period presented, with an option to apply such amendments retrospectively with a cumulative-effect adjustment to the opening balance of retained earnings as of the earliest period presented. The amendments for market risk benefits are to be applied retrospectively. We are currently evaluating the effects the adoption of ASU 2018-12 will have on our consolidated financial position, results of operations, cash flows, and related disclosures. There were no other new accounting pronouncements that were issued or became effective since the issuance of our 2019 Annual Report on Form 10-K that had, or are expected to have, a material impact on our consolidated financial position, results of operations or cash flows.