| **Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions** | Dec. 31, 2015 | Dec. 31, 2014 |
|-----------------------------------------------------------------------------------------------------|---------------|---------------|
| Cost or Amortized Cost                                                                              | $ 37,444      | $ 37,545      |
| Gross Unrealized Gain                                                                               | 2,717         | 3,544         |
| Gross Unrealized Loss                                                                               | 392           | 99            |
| Estimated fair value                                                                                | 39,769        | 40,990        |
| Corporate and other bonds [Member]                                                                  |          |          |
| Cost or Amortized Cost                                                                              | 17,080        | 17,210        |
| Gross Unrealized Gain                                                                               | 1,019         | 1,721         |
| Gross Unrealized Loss                                                                               | 342           | 61            |
| Estimated fair value                                                                                | 17,757        | 18,870        |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| States, municipalities and political subdivisions [Member]                                          |          |          |
| Cost or Amortized Cost                                                                              | 11,729        | 11,285        |
| Gross Unrealized Gain                                                                               | 1,453         | 1,463         |
| Gross Unrealized Loss                                                                               | 8             | 8             |
| Estimated fair value                                                                                | 13,174        | 12,740        |
| Unrealized OTTI Losses (Gains)                                                                      | (4)           | 0             |
| Residential mortgage-backed [Member]                                                                |          |          |
| Cost or Amortized Cost                                                                              | 4,935         | 5,028         |
| Gross Unrealized Gain                                                                               | 154           | 218           |
| Gross Unrealized Loss                                                                               | 17            | 13            |
| Estimated fair value                                                                                | 5,072         | 5,233         |
| Unrealized OTTI Losses (Gains)                                                                      | (37)          | (53)          |
| Commercial mortgage-backed [Member]                                                                 |          |          |
| Cost or Amortized Cost                                                                              | 2,154         | 2,056         |
| Gross Unrealized Gain                                                                               | 55            | 93            |
| Gross Unrealized Loss                                                                               | 12            | 5             |
| Estimated fair value                                                                                | 2,197         | 2,144         |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | (2)           |
| Other asset-backed [Member]                                                                         |          |          |
| Cost or Amortized Cost                                                                              | 923           | 1,234         |
| Gross Unrealized Gain                                                                               | 6             | 11            |
| Gross Unrealized Loss                                                                               | 8             | 10            |
| Estimated fair value                                                                                | 921           | 1,235         |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| Total asset-backed [Member]                                                                         |          |          |
| Cost or Amortized Cost                                                                              | 8,012         | 8,318         |
| Gross Unrealized Gain                                                                               | 215           | 322           |
| Gross Unrealized Loss                                                                               | 37            | 28            |
| Estimated fair value                                                                                | 8,190         | 8,612         |
| Unrealized OTTI Losses (Gains)                                                                      | (37)          | (55)          |
| U.S. Treasury and obligations of government-sponsored enterprises [Member]                          |          |          |
| Cost or Amortized Cost                                                                              | 62            | 26            |
| Gross Unrealized Gain                                                                               | 5             | 5             |
| Gross Unrealized Loss                                                                               | 0             | 0             |
| Estimated fair value                                                                                | 67            | 31            |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| Foreign Government Debt Securities [Member]                                                         |          |          |
| Cost or Amortized Cost                                                                              | 334           | 438           |
| Gross Unrealized Gain                                                                               | 13            | 16            |
| Gross Unrealized Loss                                                                               | 1             | 0             |
| Estimated fair value                                                                                | 346           | 454           |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| Redeemable preferred stock [Member]                                                                 |          |          |
| Cost or Amortized Cost                                                                              | 33            | 39            |
| Gross Unrealized Gain                                                                               | 2             | 3             |
| Gross Unrealized Loss                                                                               | 0             | 0             |
| Estimated fair value                                                                                | 35            | 42            |
| Unrealized OTTI Losses (Gains)                                                                      | 0             | 0             |
| Total fixed maturity securities available-for-sale [Member]                                         |          |          |
| Cost or Amortized Cost                                                                              | 37,250        | 37,316        |
| Gross Unrealized Gain                                                                               | 2,707         | 3,530         |
| Gross Unrealized Loss                                                                               | 388           | 97            |
| Estimated fair value                                                                                | 39,569        | 40,749        |
| Unrealized OTTI Losses (Gains)                                                                      | (41)          | (55)          |
| Total fixed maturity securities trading [Member]                                                    |          |          |
| Cost or Amortized Cost, Trading Securities                                                          | 3             | 19            |
| Estimated Fair Value, Trading Securities                                                            | 3             | 19            |
| Common stock [Member]                                                                               |          |          |
| Cost or Amortized Cost                                                                              | 46            | 38            |
| Gross Unrealized Gain                                                                               | 3             | 9             |
| Gross Unrealized Loss                                                                               | 1             | 0             |
| Estimated fair value                                                                                | 48            | 47            |
| Preferred stock [Member]                                                                            |          |          |
| Cost or Amortized Cost                                                                              | 145           | 172           |
| Gross Unrealized Gain                                                                               | 7             | 5             |
| Gross Unrealized Loss                                                                               | 3             | 2             |
| Estimated fair value                                                                                | 149           | 175           |
| Total equity securities available-for-sale [Member]                                                 |          |          |
| Cost or Amortized Cost                                                                              | 191           | 210           |
| Gross Unrealized Gain                                                                               | 10            | 14            |
| Gross Unrealized Loss                                                                               | 4             | 2             |
| Estimated fair value                                                                                | $ 197         | $ 222         |

| X                                                                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The accumulated unrealized gain or loss position on Other Than Temporary Impariment (OTTI) 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
Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563
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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.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Cost of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.
+ References
No definition available.
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