| **General (Narrative) (Details) - USD ($) $ in Millions**                        | Mar. 31, 2020 | Jan. 01, 2020 | Dec. 31, 2019 |
|----------------------------------------------------------------------------------|---------------|---------------|---------------|
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]** |          |          |          |
| Retained earnings                                                                | $ 8,634       |          | $ 9,348       |
| Mortgage loans                                                                   | 1,021         |          | 994           |
| Deferred income taxes                                                            | $ 518         |          | $ 199         |
| Accounts receivable, allowance for credit loss                                   |          | $ 6           |          |
| CNAF Consolidated | Loews                                                        |          |          |          |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]** |          |          |          |
| Noncontrolling interest, ownership percentage by parent                          | 89.00%        |          |          |
| Accounting Standards Update 2016-13                                              |          |          |          |
| **New Accounting Pronouncements or Change in Accounting Principle [Line Items]** |          |          |          |
| Retained earnings                                                                |          | 5             |          |
| Mortgage loans                                                                   |          | 7             |          |
| Deferred income taxes                                                            |          | $ 2           |          |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of allowance for credit loss on accounts receivable.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount, after allocation of valuation allowances and deferred tax liability, of deferred tax asset attributable to deductible differences and carryforwards, with jurisdictional netting.
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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.
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| - Definition
The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.
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| - Definition
The cumulative amount of the reporting entity's undistributed earnings or deficit.
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| X                                                                                                                           |
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