| **Investments (Summary of fixed maturity and equity securities) (Details) (USD $)In Millions, unless otherwise specified** | Jun. 30, 2012 | Dec. 31, 2011 |
|----------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | $ 38,137      | $ 37,633      |
| Gross Unrealized Gains                                                                                                     | 3,834         | 3,149         |
| Gross Unrealized Losses                                                                                                    | 314           | 541           |
| Estimated Fair Value                                                                                                       | 41,657        | 40,241        |
| Corporate and other bonds [Member]                                                                                         |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 19,350        | 19,086        |
| Gross Unrealized Gains                                                                                                     | 2,209         | 1,946         |
| Gross Unrealized Losses                                                                                                    | 79            | 154           |
| Estimated Fair Value                                                                                                       | 21,480        | 20,878        |
| Unrealized OTTI Losses (Gains)                                                                                             |     |     |
| States, municipalities and political subdivisions [Member]                                                                 |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 9,225         | 9,018         |
| Gross Unrealized Gains                                                                                                     | 1,225         | 900           |
| Gross Unrealized Losses                                                                                                    | 66            | 136           |
| Estimated Fair Value                                                                                                       | 10,384        | 9,782         |
| Unrealized OTTI Losses (Gains)                                                                                             |     |     |
| Residential mortgage-backed [Member]                                                                                       |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 5,817         | 5,786         |
| Gross Unrealized Gains                                                                                                     | 215           | 172           |
| Gross Unrealized Losses                                                                                                    | 141           | 183           |
| Estimated Fair Value                                                                                                       | 5,891         | 5,775         |
| Unrealized OTTI Losses (Gains)                                                                                             | 42            | 99            |
| Commercial mortgage-backed [Member]                                                                                        |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 1,514         | 1,365         |
| Gross Unrealized Gains                                                                                                     | 82            | 48            |
| Gross Unrealized Losses                                                                                                    | 27            | 59            |
| Estimated Fair Value                                                                                                       | 1,569         | 1,354         |
| Unrealized OTTI Losses (Gains)                                                                                             | (2)           | (2)           |
| Other asset-backed [Member]                                                                                                |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 1,046         | 946           |
| Gross Unrealized Gains                                                                                                     | 20            | 13            |
| Gross Unrealized Losses                                                                                                    | 1             | 4             |
| Estimated Fair Value                                                                                                       | 1,065         | 955           |
| Unrealized OTTI Losses (Gains)                                                                                             |     |     |
| Total asset-backed [Member]                                                                                                |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 8,377         | 8,097         |
| Gross Unrealized Gains                                                                                                     | 317           | 233           |
| Gross Unrealized Losses                                                                                                    | 169           | 246           |
| Estimated Fair Value                                                                                                       | 8,525         | 8,084         |
| Unrealized OTTI Losses (Gains)                                                                                             | 40            | 97            |
| U.S. Treasury and obligations of government-sponsored enterprises [Member]                                                 |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 172           | 479           |
| Gross Unrealized Gains                                                                                                     | 12            | 14            |
| Gross Unrealized Losses                                                                                                    |     |     |
| Estimated Fair Value                                                                                                       | 184           | 493           |
| Unrealized OTTI Losses (Gains)                                                                                             |     |     |
| Foreign government [Member]                                                                                                |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 616           | 608           |
| Gross Unrealized Gains                                                                                                     | 23            | 28            |
| Gross Unrealized Losses                                                                                                    |     |     |
| Estimated Fair Value                                                                                                       | 639           | 636           |
| Unrealized OTTI Losses (Gains)                                                                                             |     |     |
| Redeemable preferred stock [Member]                                                                                        |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 101           | 51            |
| Gross Unrealized Gains                                                                                                     | 10            | 7             |
| Gross Unrealized Losses                                                                                                    |     |     |
| Estimated Fair Value                                                                                                       | 111           | 58            |
| Unrealized OTTI Losses (Gains)                                                                                             |     |     |
| Total fixed maturity securities available-for-sale [Member]                                                                |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 37,841        | 37,339        |
| Gross Unrealized Gains                                                                                                     | 3,796         | 3,128         |
| Gross Unrealized Losses                                                                                                    | 314           | 536           |
| Estimated Fair Value                                                                                                       | 41,323        | 39,931        |
| Unrealized OTTI Losses (Gains)                                                                                             | 40            | 97            |
| Total fixed maturity securities trading [Member]                                                                           |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost, Trading Securities                                                                                 | 44            | 6             |
| Gross Unrealized Gains, Trading Securities                                                                                 |     |     |
| Gross Unrealized Losses, Trading Securities                                                                                |     |     |
| Estimated Fair Value, Trading Securities                                                                                   | 44            | 6             |
| Common stock [Member]                                                                                                      |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 27            | 30            |
| Gross Unrealized Gains                                                                                                     | 21            | 17            |
| Gross Unrealized Losses                                                                                                    |     |     |
| Estimated Fair Value                                                                                                       | 48            | 47            |
| Preferred stock [Member]                                                                                                   |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 225           | 258           |
| Gross Unrealized Gains                                                                                                     | 17            | 4             |
| Gross Unrealized Losses                                                                                                    |     | 5             |
| Estimated Fair Value                                                                                                       | 242           | 257           |
| Total equity securities available-for-sale [Member]                                                                        |          |          |
| **Fixed Maturity and Equity Securities**                                                                                   |          |          |
| Cost or Amortized Cost                                                                                                     | 252           | 288           |
| Gross Unrealized Gains                                                                                                     | 38            | 21            |
| Gross Unrealized Losses                                                                                                    |     | 5             |
| Estimated Fair Value                                                                                                       | $ 290         | $ 304         |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of other than temporary impairment (OTTI) loss on a debt security, categorized as Available-for-sale, related to factors other than credit losses when the entity does not intend to sell the security and it is not more likely than not that the entity will be required to sell the security before recovery of its amortized cost basis.
+ References
No definition available.
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| X                                                                                                                                                                    |
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| X                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Trading Securities, Unrealized Holding Gains
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Trading Securities, Unrealized Holding Losses
+ References
No definition available.
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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
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 7 -Footnote 2 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 19 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 12 -Subparagraph b -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 133 -Paragraph 22 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 13, 19 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27161-111563
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| X                                                                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the gross unrealized losses for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents a parenthetical disclosure for the cost of securities classified as trading.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Trading Securities which consist of all investments in certain debt and equity securities that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time) or for which an entity has elected the fair value option. Trading generally reflects active and frequent buying and selling, and trading securities are generally used with the objective of generating profits on short-term differences in price, but this category of investments may also include items which are not intended to be sold in the near term or for which the fair value option has been elected.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 115 -Paragraph 12 -Subparagraph a -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.  This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789
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