| **Fair Value Measurements (Fair Value Hierarchy For Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions** | Dec. 31, 2019 | Dec. 31, 2018 |
|---------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | $ 11,698      | $ 10,689      |
| Available for sale securities, equity securities                                                                                            | 7,752         | 5,920         |
| Separate accounts taxable fixed maturities                                                                                                  | 882           | 803           |
| Total                                                                                                                                       | 20,350        | 17,434        |
| Top Hat Savings Plan - Mutual Funds and Common Equities                                                                                     |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Top Hat savings plan mutual funds and common equity (included in Other assets)                                                              | 45            | 34            |
| Level 1                                                                                                                                     |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Total                                                                                                                                       | 7,667         | 5,843         |
| Level 1 | Top Hat Savings Plan - Mutual Funds and Common Equities                                                                           |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Top Hat savings plan mutual funds and common equity (included in Other assets)                                                              | 45            | 34            |
| Level 2                                                                                                                                     |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Total                                                                                                                                       | 12,683        | 11,586        |
| Level 2 | Top Hat Savings Plan - Mutual Funds and Common Equities                                                                           |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Top Hat savings plan mutual funds and common equity (included in Other assets)                                                              | 0             | 0             |
| Level 3                                                                                                                                     |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Total                                                                                                                                       | 0             | 5             |
| Level 3 | Top Hat Savings Plan - Mutual Funds and Common Equities                                                                           |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Top Hat savings plan mutual funds and common equity (included in Other assets)                                                              | 0             | 0             |
| Fixed Maturities                                                                                                                            |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 11,698        | 10,689        |
| Fixed Maturities | Corporate Securities                                                                                                     |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 6,401         | 5,710         |
| Fixed Maturities | States, Municipalities and Political Subdivisions                                                                        |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 4,728         | 4,304         |
| Fixed Maturities | Commercial Mortgage Backed Securities                                                                                    |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 301           | 288           |
| Fixed Maturities | Government-Sponsored Enterprises                                                                                         |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 136           | 310           |
| Fixed Maturities | United States Government                                                                                                 |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 104           | 67            |
| Fixed Maturities | Foreign Government                                                                                                       |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 28            | 10            |
| Fixed Maturities | Level 1                                                                                                                  |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 104           | 67            |
| Fixed Maturities | Level 1 | Corporate Securities                                                                                           |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Fixed Maturities | Level 1 | States, Municipalities and Political Subdivisions                                                              |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Fixed Maturities | Level 1 | Commercial Mortgage Backed Securities                                                                          |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Fixed Maturities | Level 1 | Government-Sponsored Enterprises                                                                               |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Fixed Maturities | Level 1 | United States Government                                                                                       |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 104           | 67            |
| Fixed Maturities | Level 1 | Foreign Government                                                                                             |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Fixed Maturities | Level 2                                                                                                                  |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 11,594        | 10,617        |
| Fixed Maturities | Level 2 | Corporate Securities                                                                                           |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 6,401         | 5,709         |
| Fixed Maturities | Level 2 | States, Municipalities and Political Subdivisions                                                              |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 4,728         | 4,300         |
| Fixed Maturities | Level 2 | Commercial Mortgage Backed Securities                                                                          |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 301           | 288           |
| Fixed Maturities | Level 2 | Government-Sponsored Enterprises                                                                               |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 136           | 310           |
| Fixed Maturities | Level 2 | United States Government                                                                                       |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Fixed Maturities | Level 2 | Foreign Government                                                                                             |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 28            | 10            |
| Fixed Maturities | Level 3                                                                                                                  |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 5             |
| Fixed Maturities | Level 3 | Corporate Securities                                                                                           |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 1             |
| Fixed Maturities | Level 3 | States, Municipalities and Political Subdivisions                                                              |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 4             |
| Fixed Maturities | Level 3 | Commercial Mortgage Backed Securities                                                                          |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Fixed Maturities | Level 3 | Government-Sponsored Enterprises                                                                               |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Fixed Maturities | Level 3 | United States Government                                                                                       |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Fixed Maturities | Level 3 | Foreign Government                                                                                             |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, debt securities                                                                                              | 0             | 0             |
| Equity Securities | Common Equities                                                                                                         |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, equity securities                                                                                            | 7,518         | 5,742         |
| Equity Securities | Nonredeemable Preferred Equities                                                                                        |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, equity securities                                                                                            | 234           | 178           |
| Equity Securities | Level 1 | Common Equities                                                                                               |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, equity securities                                                                                            | 7,518         | 5,742         |
| Equity Securities | Level 1 | Nonredeemable Preferred Equities                                                                              |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, equity securities                                                                                            | 0             | 0             |
| Equity Securities | Level 2 | Common Equities                                                                                               |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, equity securities                                                                                            | 0             | 0             |
| Equity Securities | Level 2 | Nonredeemable Preferred Equities                                                                              |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, equity securities                                                                                            | 234           | 178           |
| Equity Securities | Level 3 | Common Equities                                                                                               |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, equity securities                                                                                            | 0             | 0             |
| Equity Securities | Level 3 | Nonredeemable Preferred Equities                                                                              |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Available for sale securities, equity securities                                                                                            | 0             | 0             |
| Taxable Fixed Maturities                                                                                                                    |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Separate accounts taxable fixed maturities                                                                                                  | 855           | 791           |
| Taxable Fixed Maturities | Level 1                                                                                                          |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Separate accounts taxable fixed maturities                                                                                                  | 0             | 0             |
| Taxable Fixed Maturities | Level 2                                                                                                          |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Separate accounts taxable fixed maturities                                                                                                  | 855           | 791           |
| Taxable Fixed Maturities | Level 3                                                                                                          |          |          |
| **Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis**                                                          |          |          |
| Separate accounts taxable fixed maturities                                                                                                  | $ 0           | $ 0           |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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| - Definition
Amount of equity securities categorized neither as held-to-maturity nor as trading.
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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.
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| - Definition
Fair value portion of investment securities, including, but not limited to, marketable securities, derivative financial instruments, and investments accounted for under the equity method.
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| - Definition
Value of the other investment not readily marketable determined by management based upon fair value methods, including pricing of similar securities and valuation techniques, that was used to record the investment for financial reporting purposes.
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| - Definition
Amount of asset at fair value held for benefit of separate account policyholder.
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