| **Investments (Components of other-than-temporary impairment losses recognized in earnings) (Details) - USD ($) $ in Millions** | 3 Months Ended | 6 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Debt Securities, Available-for-sale [Line Items]**                                                                            |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | $ 0            | $ 2            | $ 6 | $ 4 |
| Corporate and other bonds                                                                                                       |           |           |   |   |
| **Debt Securities, Available-for-sale [Line Items]**                                                                            |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | 0              | 2              | 5 | 4 |
| Asset-backed                                                                                                                    |           |           |   |   |
| **Debt Securities, Available-for-sale [Line Items]**                                                                            |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | $ 0            | $ 0            | $ 1 | $ 0 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of other-than-temporary impairment (OTTI) on investment in debt security, recognized in earnings.
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8A -URI http://asc.fasb.org/extlink&oid=109979856&loc=SL6284422-111562
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| 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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