| **Investments (Analysis Of Cost Or Amortized Cost Gross Unrealized Gains And Losses And Fair Value For Investments) (Details) - USD ($) $ in Millions** | Dec. 31, 2017 | Dec. 31, 2016 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| Fixed Maturities                                                                                                                                        |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | $ 10,314      | $ 9,799       |
| Gross unrealized gains                                                                                                                                  | 409           | 359           |
| Gross unrealized losses                                                                                                                                 | 24            | 73            |
| Fair value                                                                                                                                              | 10,699        | 10,085        |
| Fixed Maturities | Corporate Securities                                                                                                                 |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 5,420         | 5,555         |
| Gross unrealized gains                                                                                                                                  | 246           | 252           |
| Gross unrealized losses                                                                                                                                 | 13            | 26            |
| Fair value                                                                                                                                              | 5,653         | 5,781         |
| Fixed Maturities | States, Municipalities and Political Subdivisions                                                                                    |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 4,316         | 3,770         |
| Gross unrealized gains                                                                                                                                  | 155           | 100           |
| Gross unrealized losses                                                                                                                                 | 6             | 42            |
| Fair value                                                                                                                                              | 4,465         | 3,828         |
| Fixed Maturities | Commercial Mortgage Backed Securities                                                                                                |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 280           | 282           |
| Gross unrealized gains                                                                                                                                  | 7             | 7             |
| Gross unrealized losses                                                                                                                                 | 1             | 2             |
| Fair value                                                                                                                                              | 286           | 287           |
| Fixed Maturities | Government-Sponsored Enterprises                                                                                                     |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 257           | 167           |
| Gross unrealized gains                                                                                                                                  | 1             | 0             |
| Gross unrealized losses                                                                                                                                 | 4             | 3             |
| Fair value                                                                                                                                              | 254           | 164           |
| Fixed Maturities | Foreign Government                                                                                                                   |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 10            | 10            |
| Gross unrealized gains                                                                                                                                  | 0             | 0             |
| Gross unrealized losses                                                                                                                                 | 0             | 0             |
| Fair value                                                                                                                                              | 10            | 10            |
| Fixed Maturities | Convertibles and Bonds with Warrants Attached                                                                                        |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  |          | 5             |
| Gross unrealized gains                                                                                                                                  |          | 0             |
| Gross unrealized losses                                                                                                                                 |          | 0             |
| Fair value                                                                                                                                              |          | 5             |
| Fixed Maturities | United States Government                                                                                                             |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 31            | 10            |
| Gross unrealized gains                                                                                                                                  | 0             | 0             |
| Gross unrealized losses                                                                                                                                 | 0             | 0             |
| Fair value                                                                                                                                              | 31            | 10            |
| Equity Securities                                                                                                                                       |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 3,094         | 2,995         |
| Gross unrealized gains                                                                                                                                  | 3,169         | 2,348         |
| Gross unrealized losses                                                                                                                                 | 14            | 9             |
| Fair value                                                                                                                                              | 6,249         | 5,334         |
| Equity Securities | Common Equities                                                                                                                     |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 2,918         | 2,812         |
| Gross unrealized gains                                                                                                                                  | 3,135         | 2,320         |
| Gross unrealized losses                                                                                                                                 | 14            | 9             |
| Fair value                                                                                                                                              | 6,039         | 5,123         |
| Equity Securities | Nonredeemable Preferred Equities                                                                                                    |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 176           | 183           |
| Gross unrealized gains                                                                                                                                  | 34            | 28            |
| Gross unrealized losses                                                                                                                                 | 0             | 0             |
| Fair value                                                                                                                                              | 210           | 211           |
| Fixed Maturities And Equity Securities                                                                                                                  |          |          |
| **Schedule of Available-for-sale Securities**                                                                                                           |          |          |
| Cost or amortized cost                                                                                                                                  | 13,408        | 12,794        |
| Gross unrealized gains                                                                                                                                  | 3,578         | 2,707         |
| Gross unrealized losses                                                                                                                                 | 38            | 82            |
| Fair value                                                                                                                                              | $ 16,948      | $ 15,419      |

| X                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.
+ References
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+ Details**Name:**us-gaap_AvailableForSaleSecuritiesAmortizedCost**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| 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.
+ Details**Name:**us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| 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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| 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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