| **Reserves in Addition to Account Balance, Based on Expected No-Lapse Guarantee Benefits and Expected Policy Assessments (Detail) - USD ($) $ in Millions** | Sep. 30, 2020 | Dec. 31, 2019 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                 |          |          |
| Life policy and investment contract reserves                                                                                                                | $ 2,900       | $ 2,835       |
| Life policy reserves:                                                                                                                                       |          |          |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                 |          |          |
| Life policy and investment contract reserves                                                                                                                | 1,338         | 1,276         |
| Life policy reserves: | Ordinary/traditional life                                                                                                           |          |          |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                 |          |          |
| Life policy and investment contract reserves                                                                                                                | 1,287         | 1,226         |
| Life policy reserves: | Other                                                                                                                               |          |          |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                 |          |          |
| Life policy and investment contract reserves                                                                                                                | 51            | 50            |
| Investment contract reserves:                                                                                                                               |          |          |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                 |          |          |
| Life policy and investment contract reserves                                                                                                                | 1,562         | 1,559         |
| Investment contract reserves: | Deferred annuities                                                                                                          |          |          |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                 |          |          |
| Life policy and investment contract reserves                                                                                                                | 760           | 760           |
| Investment contract reserves: | Universal life                                                                                                              |          |          |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                 |          |          |
| Life policy and investment contract reserves                                                                                                                | 646           | 640           |
| Investment contract reserves: | Structured Settlement Annuity                                                                                               |          |          |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                 |          |          |
| Life policy and investment contract reserves                                                                                                                | 147           | 151           |
| Investment contract reserves: | Other                                                                                                                       |          |          |
| **Liability for Future Policy Benefit, by Product Segment**                                                                                                 |          |          |
| Life policy and investment contract reserves                                                                                                                | $ 9           | $ 8           |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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.
+ References
No definition available.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of accrued obligation to policyholders that relates to insured events under long-term life insurance contracts.
+ References
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| X                                                                                                                                                           |
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| X                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                    |
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| X                                                                                                                                             |
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| X                                                                                                                                            |
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| X                                                                                                                                                          |
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| X                                                                                                                                                           |
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