Basis of Presentation (Policies)	6 Months Ended
Basis of Presentation (Policies)	Jun. 30, 2018
Accounting Policies [Abstract]
Basis of Accounting	Loews Corporation is a holding company. Its subsidiaries are engaged in the following lines of business: commercial property and casualty insurance (CNA Financial Corporation (“CNA”), a 89% owned subsidiary); the operation of offshore oil and gas drilling rigs (Diamond Offshore Drilling, Inc. (“Diamond Offshore”), a 53% owned subsidiary); transportation and storage of natural gas and natural gas liquids (Boardwalk Pipeline Partners, LP (“Boardwalk Pipeline”), a wholly owned subsidiary); the operation of a chain of hotels (Loews Hotels Holding Corporation (“Loews Hotels & Co”), a wholly owned subsidiary); and the manufacture of rigid plastic packaging solutions (Consolidated Container Company LLC (“Consolidated Container”), a 99% owned subsidiary). Unless the context otherwise requires, the terms “Company,” “Loews” and “Registrant” as used herein mean Loews Corporation excluding its subsidiaries and the term “Net income attributable to Loews Corporation” as used herein means Net income attributable to Loews Corporation shareholders. In the opinion of management, the accompanying unaudited Consolidated Condensed Financial Statements reflect all adjustments (consisting of normal recurring accruals) necessary to present fairly the Company’s financial position as of June 30, 2018 and December 31, 2017, results of operations and comprehensive income for the three and six months ended June 30, 2018 and 2017 and changes in shareholders’ equity and cash flows for the six months ended June 30, 2018 and 2017. Net income for the second quarter and first half of each of the years is not necessarily indicative of net income for that entire year. These Consolidated Condensed Financial Statements should be read in conjunction with the Consolidated Financial Statements in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017.
Income Per Share	The Company presents basic and diluted net income per share on the Consolidated Condensed Statements of Income. Basic net income per share excludes dilution and is computed by dividing net income attributable to common stock by the weighted average number of common shares outstanding for the period. Diluted net income per share reflects the potential dilution that could occur if securities or other contracts to issue common stock were exercised or converted into common stock. There were no shares and 0.6 million shares attributable to employee stock-based compensation awards excluded from the diluted weighted average shares outstanding amounts for the three and six months ended June 30, 2018 and 2017 because the effect would have been antidilutive.
Revenue from Contracts with Customers	In May of 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) ASU 2014-09, “Revenue from Contracts with Customers (Topic 606)” (“ASU 2014-09”). The core principle of the new accounting guidance is that a company should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. The new accounting guidance provides a five-step analysis of transactions to determine when and how revenue is recognized and requires enhanced disclosures about revenue. The standard excludes from its scope the accounting for insurance contracts, financial instruments and certain other agreements that are subject to other guidance in the FASB Accounting Standards Codification, which limits the impact of this change in accounting for the Company. On January 1, 2018, the Company adopted the updated accounting guidance using the modified retrospective method, with a cumulative effect adjustment to the opening balance sheet. Upon adoption, the new guidance was applied to all contracts subject to the standard that were not completed as of the date of adoption. Prior period amounts have not been adjusted and continue to be reported in accordance with the previous accounting guidance. At adoption, the cumulative effect adjustment decreased beginning Retained earnings by $62 million (after tax and noncontrolling interests), resulted in a deferred tax asset of $23 million and increased Other assets by approximately $1.9 billion and Other liabilities by approximately $2.0 billion. The impact of the new guidance is primarily related to revenue on CNA’s non-insurance warranty products and services, which will be recognized more slowly as compared to the historic revenue recognition pattern. For the warranty products in which CNA acts as principal, Operating revenues and other and Operating expenses and other are increased to reflect the gross amount paid by consumers, including the retail seller’s markup, which is considered a commission to the Company’s agent. This gross-up of revenues and expenses resulted in an increase to Other assets and Other liabilities on the Consolidated Condensed Balance Sheet, as the revenue and expense are recognized over the actuarially determined expected claims emergence pattern. Prior to the adoption of ASU 2014-09, Other assets and Other liabilities would have been $2.7 billion and $7.0 billion as of June 30, 2018, as compared to $2.6 billion and $5.5 billion as of December 31, 2017. The impact of adopting the new guidance resulted in an increase to Operating revenues and other of $143 million and $274 million for the three and six months ended June 30, 2018 and an increase to Operating expenses and other of $141 million and $274 million for the three and six months ended June 30, 2018. See Note 7 for additional information on revenues from contracts with customers.
Recognition and Measurement of Financial Assets and Financial Liabilities	In January of 2016, the FASB issued ASU 2016-01, “Financial Instruments – Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities” (“ASU 2016-01”). The updated accounting guidance requires changes to the reporting model for financial instruments. The guidance primarily changes the model for equity securities by requiring changes in the fair value of equity securities (except those accounted for under the equity method of accounting, those without readily determinable fair values and those that result in consolidation of the investee) to be recognized through the income statement. With the adoption of the new guidance, equity securities are no longer classified as available-for-sale or trading. Prior period amounts have not been adjusted and continue to be reported in accordance with the previous accounting guidance. As of January 1, 2018, the Company adopted the updated accounting guidance and recognized a cumulative effect adjustment of $25 million (after tax and noncontrolling interests) as an increase to beginning Retained earnings. For the three and six months ended June 30, 2018, a decrease in the fair value of equity securities of approximately $8 million and $23 million was recognized in the Company’s Consolidated Condensed Statements of Income as a result of this change. For the three and six months ended June 30, 2017, a $2 million and $6 million increase in the fair value of equity securities was recognized in Other comprehensive income.
Income Taxes	In October of 2016, the FASB issued ASU 2016-16, “Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory.” The updated guidance amends the accounting for the income tax consequences of intra-entity transfers of assets other than inventory. As of January 1, 2018, the Company adopted this updated guidance using the modified retrospective approach with a cumulative effect adjustment of $9 million (after noncontrolling interests) as a decrease to beginning Retained earnings with an offset to a deferred income tax liability.
Income Statement-Reporting Comprehensive Income	In February of 2018, the FASB issued ASU 2018-02, “Income Statement—Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income” (“ASU 2018-02”). Current accounting guidance requires the remeasurement of deferred tax liabilities and assets due to a change in tax laws or rates with the effect included in Net income in the reporting period that includes the enactment date. Because the remeasurement of deferred taxes due to a reduction in the federal corporate income tax rate under the Tax Cuts and Jobs Act of 2017 (the “Tax Act”) is required to be included in Net income, the tax effects of items within Accumulated Other Comprehensive Income (“AOCI”) do not reflect the appropriate rate (referred to as “stranded tax effects”). The updated accounting guidance allows a reclassification from AOCI to Retained earnings for the stranded tax effects resulting from the Tax Act. The Company early adopted the updated guidance effective January 1, 2018 and elected to reclassify the stranded tax effects from AOCI to Retained earnings. The impact of the change resulted in a $3 million (after noncontrolling interests) increase in Retained earnings and a corresponding decrease in AOCI. The decrease in AOCI is comprised of a $130 million (after noncontrolling interests) decrease in pension liability and a $127 million (after noncontrolling interests) increase in unrealized gains (losses) on investments. The Company releases tax effects from AOCI utilizing the security-by-security approach for investments and using enacted tax rates based on the pretax adjustments for pension and postretirement benefits.
Recently issued ASUs	Recently issued ASUs – In February of 2016, the FASB issued ASU 2016-02, “Leases (Topic 842).” The updated guidance requires lessees to recognize lease assets and lease liabilities for most operating leases. In addition, the updated guidance requires that lessors separate lease and nonlease components in a contract in accordance with the new revenue guidance in ASU 2014-09. The updated guidance is effective for interim and annual periods beginning after December 15, 2018. The Company is currently evaluating the effect the guidance will have on its consolidated financial statements. In June of 2016, the FASB issued ASU 2016-13, “Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments.” The updated accounting guidance requires changes to the recognition of credit losses on financial instruments not accounted for at fair value through net income. The guidance is effective for interim and annual periods beginning after December 15, 2019. The Company is currently evaluating the effect the guidance will have on its consolidated financial statements, and expects the primary changes to be the use of the expected credit loss model for the mortgage loan portfolio and reinsurance receivables and the use of the allowance method rather than the write-down method for credit losses within the available-for-sale fixed maturities portfolio. The expected credit loss model will require a financial asset to be presented at the net amount expected to be collected. Under the allowance method for available-for-sale debt securities the Company will record reversals of credit losses if the estimate of credit losses declines. Income tax reform update – Based on the Company’s interpretation of the Tax Act, a non-cash provisional $200 million increase to net income (net of noncontrolling interests) was recorded during the fourth quarter of 2017. This increase included a one-time mandatory repatriation of previously deferred earnings of certain of Diamond Offshore’s non-U.S. subsidiaries inclusive of the utilization of certain tax attributes offset by a provisional liability for uncertain tax positions related to such attributes. In 2018, the U.S. Department of the Treasury and the Internal Revenue Service issued additional guidance which clarified certain of Diamond Offshore’s tax positions, which resulted in a $23 million increase to net income (net of noncontrolling interests) in the first quarter of 2018 for uncertain tax positions related to the mandatory repatriation toll charges in accordance with the Securities and Exchange Commission’s Staff Accounting Bulletin No. 118 (“SAB 118”). SAB 118 allows companies to report the income tax effects of the Tax Act as a provisional amount based on a reasonable estimate, which would be subject to adjustment during a reasonable measurement period, not to exceed twelve months, until the accounting and analysis under ASC 740 is complete. The Company is still in the process of evaluating the estimate as it relates to the tax effect of: (i) the amount of deferred tax assets and liabilities subject to the income tax rate change from 35% to 21%, including the calculation of the mandatory deemed repatriation aspect of the Tax Act and the state tax effect of adjustments made to the federal temporary differences, (ii) the ability to more likely than not realize the benefit of deferred tax assets, including net operating losses and foreign tax credits, (iii) the effect of re-computing CNA’s insurance reserves and the transition adjustment from existing law, the effects of which will have no impact on the effective tax rate and (iv) the special accounting method provisions for recognizing income for U.S. federal income tax purposes no later than financial accounting purposes and the transition adjustment from existing law, which will also have no impact on the effective tax rate.

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.