| **Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) shares in Thousands, $ in Millions**         | 3 Months Ended | 9 Months Ended | 12 Months Ended |                   |
|---------------------------------------------------------------------------------------------------------------------------|----------------|----------------|-----------------|-------------------|
||
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Decrease accumulated other comprehensive income                                                                           |           |           |            | $ (8,825)         | $ (12,809) | $ (12,707) |   |
| Anticipated amounts due from insureds related to losses under deductible policies                                         |           |           |            | $ 1,100           | $ 1,100 |   |   |
| Structured settlement annuities, interest rate, low end                                                                   |           |           |            | 6.40%             | 6.40% |   |   |
| Discounted reserves for unfunded structured settlements                                                                   |           |           |            | $ 485             | $ 503 |   |   |
| Discounted reserves for unfunded structure settlements, discount amount                                                   |           |           |            | 590               | 621 |   |   |
| Amount of interest recognized on the discounted reserves of unfunded structured settlements                               |           |           |            | $ 36              | $ 36 | 35 |   |
| Interest rates at which workers' compensation lifetime claim reserves are discounted at                                   |           |           |            | 3.50%             | 3.50% |   |   |
| Workers' compensation liability                                                                                           |           |           |            | $ 211             | $ 228 |   |   |
| Discounted reserves for workers’ compensation lifetime claim reserves, discount amount                              |           |           |            | 93                | 97 |   |   |
| Amount of interest accretion recognized on the discounted reserves of workers’ compensation lifetime claim reserves |           |           |            | $ 9               | $ 12 | $ 15 |   |
| Long term care claim reserves weighted average discounted interest rate                                                   |           |           |            | 5.90%             | 5.80% |   |   |
| Discounted reserves for long term care claim reserves                                                                     |           |           |            | $ 2,800           | $ 2,700 |   |   |
| Premium deficiency                                                                                                        |           |           |            | $ 450             | $ 428 |   |   |
| Liability for future policy benefits, gross premium valuation, pretax margin                                              | $ 125          | $ 72           | $ 125           |              |   |   |   |
| Minimum interest rate used to calculate reserves for long term care products                                              |           |           |            | 5.30%             | 5.30% |   |   |
| Liability balance for guaranty fund                                                                                       |           |           |            | $ 74              | $ 79 |   |   |
| Percentage of billed receivables compared to total reinsurance receivable                                                 |           |           |            | 5.00%             |   |   |   |
| Policyholder dividends, rate on policy earnings                                                                           |           |           |            | 2.00%             | 1.00% | 1.00% |   |
| Increase (decrease) in shadow adjustment, net of tax                                                                      |           |           |            | $ 2,416           | $ 296 |   |   |
| Reduction of net unrealized gains on investments included in AOCI due to shadow adjustments                               |           |           |            | 61                | 2,477 |   |   |
| Foreign currency transaction gain (loss), before tax                                                                      |           |           |            | $ (22)            | $ (1) | $ 13 |   |
| Operating lease, right-of-use asset, statement of financial position [Extensible List]                                    |           |           |            | Other Assets      | Other Assets |   |   |
| Operating lease, liability, statement of financial position [Extensible List]                                             |           |           |            | Other liabilities | Other liabilities |   |   |
| Weighted average number diluted shares outstanding adjustment (in shares)                                                 |           |           |            | 1,000             | 1,000 | 1,000 |   |
| Interest paid, net                                                                                                        |           |           |            | $ 109             | $ 110 | $ 124 |   |
| Income taxes paid                                                                                                         |           |           |            | $ 277             | 278 | 108 |   |
| Furniture and Fixtures                                                                                                    |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Property, plant and equipment, useful life                                                                                |           |           |            | 7 years           |   |   |   |
| Office Equipment                                                                                                          |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Property, plant and equipment, useful life                                                                                |           |           |            | 5 years           |   |   |   |
| Computer Software, Intangible Asset                                                                                       |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Property, plant and equipment, useful life                                                                                |           |           |            | 10 years          |   |   |   |
| Minimum                                                                                                                   |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Warranty coverage term                                                                                                    |           |           |            | 1 month           |   |   |   |
| Requisite service period for stock- based compensation expense                                                            |           |           |            | 3 years           |   |   |   |
| Minimum | Computer Software, Intangible Asset                                                                             |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Property, plant and equipment, useful life                                                                                |           |           |            | 3 years           |   |   |   |
| Maximum                                                                                                                   |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Warranty coverage term                                                                                                    |           |           |            | 10 years          |   |   |   |
| Maximum | Computer Software, Intangible Asset                                                                             |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Property, plant and equipment, useful life                                                                                |           |           |            | 5 years           |   |   |   |
| CNAF Consolidated | Loews                                                                                                 |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Noncontrolling interest, ownership percentage by parent                                                                   |           |           |            | 90.00%            |   |   |   |
| Accumulated Other Comprehensive (Loss) Income                                                                             |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Decrease accumulated other comprehensive income                                                                           |           |           |            | $ 3,557           | $ (320) | (803) | $ (51) |
| Accumulated Other Comprehensive (Loss) Income | Revision of Prior Period, Accounting Standards Update, Adjustment         |           |           |            |              |   |   |   |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]**                                          |           |           |            |              |   |   |   |
| Decrease accumulated other comprehensive income                                                                           |           |           |            |              |   | $ 2,300 |   |

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Amount of interest accretion recognized on the discounted reserves of workers’ compensation lifetime claim reserves
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Amount of interest recognized on the discounted reserves of unfunded structured settlements
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Losses under deductible policies
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Discounted reserves for unfunded structured settlements
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Discounted reserves for long term care claim reserves
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Discounted reserves for long term care claim reserves, discount amount
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Increase (decrease) in shadow adjustment, net of tax
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Liability for Future Policy Benefits, Gross Premium Valuation, Pretax Margin
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Long term Care Claim Reserves Weighted Average Discounted Interest Rate
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Percentage Of Billed Receivables Compared To Total Reinsurance Receivable
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Reduction of net unrealized gains on investments included in AOCI due to shadow adjustments
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Structured Settlement Annuities, Interest Rates, Low End
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Warranty Coverage Term
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Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement.
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| - Definition
The amount of cash paid during the current period to foreign, federal, state, and local authorities as taxes on income.
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| - Definition
Amount of cash paid for interest, excluding capitalized interest, classified as operating activity. Includes, but is not limited to, payment to settle zero-coupon bond for accreted interest of debt discount and debt instrument with insignificant coupon interest rate in relation to effective interest rate of borrowing attributable to accreted interest of debt discount.
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| - Definition
The assumed interest rate used to determine present value of future benefits to be paid to or on behalf of policyholders and related expenses less the present value of future net premiums using assumptions such as estimates of expected investment yields, mortality, morbidity, terminations and expenses, applicable at the time the insurance contracts are made and unpaid claim costs relating to insurance contracts including estimates of costs relating to incurred but not reported claims based on the estimated ultimate cost of settling the claims (including effects of inflation and other societal and economic factors), using past experience adjusted for current trends and any other factors that would modify past experience in the year the policy went into force.
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| - Definition
The liability as of the balance sheet date representing required funding mandated by statute or regulatory authority that is related directly or indirectly to underwriting activities, including pools for self-insurance and excluding premium taxes and income taxes. The funds derived from the assessments generally enable a government guarantor to pay insurance claims in the event that the underwriting insurer is insolvent or otherwise unable to meet its payment obligations.
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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
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Indicates line item in statement of financial position that includes operating lease liability.
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Indicates line item in statement of financial position that includes operating lease right-of-use asset.
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| - Definition
The percentage of earnings allocable to participating policyholders based on earnings of such policies for payment of dividends.
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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.
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| - Definition
Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
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| - Definition
Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.
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| - Definition
The sum of dilutive potential common shares or units used in the calculation of the diluted per-share or per-unit computation.
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| - Definition
Current year monetary amount of the change in worker's compensation reserve liability resulting from the discount applied to reduce the reserve to present value.
+ References
No definition available.
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| - Definition
Percent discount applied to worker's compensation reserve liability to reduce the reserve to present value.
+ References
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| - Definition
Carrying value as of the balance sheet date of obligations and payables pertaining to claims incurred of a workers compensation nature.
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