| **Investments - Components of other-than-temporary impairment losses recognized in earnings (Details) - USD ($) $ in Millions** | 3 Months Ended | 6 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Schedule of Available-for-sale Securities [Line Items]**                                                                      |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | $ 2            | $ 15           | $ 4 | $ 38 |
| Corporate and other bonds                                                                                                       |           |           |   |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                      |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | 2              | 13             | 4 | 29 |
| Residential mortgage-backed                                                                                                     |           |           |   |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                      |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | 0              | 1              | 0 | 1 |
| Other asset-backed                                                                                                              |           |           |   |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                      |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | 0              | 1              | 0 | 3 |
| Total asset-backed                                                                                                              |           |           |   |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                      |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | 0              | 2              | 0 | 4 |
| Total fixed maturity securities available-for-sale                                                                              |           |           |   |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                      |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | 2              | 15             | 4 | 33 |
| Equity securities available-for-sale -- Common stock                                                                            |           |           |   |   |
| **Schedule of Available-for-sale Securities [Line Items]**                                                                      |           |           |   |   |
| OTTI losses recognized in earnings                                                                                              | $ 0            | $ 0            | $ 0 | $ 5 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 8B -URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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.
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