| **Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) $ in Millions** | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Dec. 31, 2017 USD ($) |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|-----------------------|-----------------------|-----------------------|
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                    |                  |                  |                  |
| Estimated fair value                                                                                                                                    | $ 44,813              | $ 41,491              |                       |
| Fixed maturity securities | Income Approach Valuation Technique                                                                                         |                  |                  |                  |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                    |                  |                  |                  |
| Estimated fair value                                                                                                                                    | $ 525                 | $ 228                 |                  |
| Measurement Input, Credit Spread | Income Approach Valuation Technique | Minimum                                                                        |                  |                  |                  |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                    |                  |                  |                  |
| Debt securities, available-for-sale, measurement Input                                                                                                  | 0.01                  | 0.01                  |                  |
| Measurement Input, Credit Spread | Income Approach Valuation Technique | Maximum                                                                        |                  |                  |                  |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                    |                  |                  |                  |
| Debt securities, available-for-sale, measurement Input                                                                                                  | 0.06                  | 0.12                  |                  |
| Measurement Input, Credit Spread | Income Approach Valuation Technique | Weighted Average                                                               |                  |                  |                  |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                    |                  |                  |                  |
| Debt securities, available-for-sale, measurement Input                                                                                                  | 0.02                  | 0.03                  |                  |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Value of input used to measure investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
+ References
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| - 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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