| **Investments (Ratings distribution of asset-backed securities in a gross unrealized loss position) (Details) (Asset-backed Securities [Member], USD $)In Millions, unless otherwise specified** | Dec. 31, 2011 | Dec. 31, 2010 |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Asset-Backed Securities**                                                                                                                                                                      |          |          |
| Amortized Cost                                                                                                                                                                                   | $ 2,828       |          |
| Estimated Fair Value                                                                                                                                                                             | 2,582         | 4,280         |
| Gross Unrealized Losses                                                                                                                                                                          | 246           | 314           |
| US Government, Government Agencies, and Government-Sponsored Enterprises [Member]                                                                                                                |          |          |
| **Asset-Backed Securities**                                                                                                                                                                      |          |          |
| Amortized Cost                                                                                                                                                                                   | 382           |          |
| Estimated Fair Value                                                                                                                                                                             | 347           |          |
| Gross Unrealized Losses                                                                                                                                                                          | 35            |          |
| AAA [Member]                                                                                                                                                                                     |          |          |
| **Asset-Backed Securities**                                                                                                                                                                      |          |          |
| Amortized Cost                                                                                                                                                                                   | 364           |          |
| Estimated Fair Value                                                                                                                                                                             | 355           |          |
| Gross Unrealized Losses                                                                                                                                                                          | 9             |          |
| AA [Member]                                                                                                                                                                                      |          |          |
| **Asset-Backed Securities**                                                                                                                                                                      |          |          |
| Amortized Cost                                                                                                                                                                                   | 409           |          |
| Estimated Fair Value                                                                                                                                                                             | 388           |          |
| Gross Unrealized Losses                                                                                                                                                                          | 21            |          |
| A [Member]                                                                                                                                                                                       |          |          |
| **Asset-Backed Securities**                                                                                                                                                                      |          |          |
| Amortized Cost                                                                                                                                                                                   | 370           |          |
| Estimated Fair Value                                                                                                                                                                             | 357           |          |
| Gross Unrealized Losses                                                                                                                                                                          | 13            |          |
| BBB [Member]                                                                                                                                                                                     |          |          |
| **Asset-Backed Securities**                                                                                                                                                                      |          |          |
| Amortized Cost                                                                                                                                                                                   | 319           |          |
| Estimated Fair Value                                                                                                                                                                             | 294           |          |
| Gross Unrealized Losses                                                                                                                                                                          | 25            |          |
| Non-investment grade [Member]                                                                                                                                                                    |          |          |
| **Asset-Backed Securities**                                                                                                                                                                      |          |          |
| Amortized Cost                                                                                                                                                                                   | 984           |          |
| Estimated Fair Value                                                                                                                                                                             | 841           |          |
| Gross Unrealized Losses                                                                                                                                                                          | $ 143         |          |

| X                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the cost of debt securities in a gross unrealized loss position, 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
No definition available.
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the excess of amortized cost basis over fair value of securities in a loss position and which are categorized neither as held-to-maturity nor trading securities.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 03-1 -Paragraph 21 -Subparagraph a -Clause 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 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 17 -Subparagraph a -Clause 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.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Emerging Issues Task Force (EITF) -Number 03-1 -Paragraph 21 -Subparagraph a(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 FASB Staff Position (FSP) -Number FAS115-1/124-1 -Paragraph 17 -Subparagraph a(1) -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 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6872113&loc=d3e27290-111563
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