| **Investments (Allowance on available-for-sale securities with credit impairments and PCD assets activity) (Details) - USD ($) $ in Millions** | 12 Months Ended |
|------------------------------------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Allowance for credit losses:**                                                                                                               |            |   |
| Balance, beginning of period                                                                                                                   | $ 40            | $ 0 |
| **Additions to the allowance for credit losses:**                                                                                              |            |   |
| Securities for which credit losses were not previously recorded                                                                                | 14              | 79 |
| Available-for-sale securities accounted for as PCD assets                                                                                      | 11              | 5 |
| **Reductions to the allowance for credit losses:**                                                                                             |            |   |
| Securities sold during the period (realized)                                                                                                   | 24              | 22 |
| Intent to sell or more likely than not will be required to sell the security before recovery of its amortized cost basis                       | 0               | 1 |
| Write-offs charged against the allowance                                                                                                       | 16              | 0 |
| Recoveries of amounts previously written off                                                                                                   | 0               | 0 |
| Additional increases or (decreases) to the allowance for credit losses on securities that had an allowance recorded in a previous period       | (7)             | (27) |
| Balance, end of period                                                                                                                         | 18              | 40 |
| Impact of adopting ASC 326                                                                                                                     |            |   |
| **Allowance for credit losses:**                                                                                                               |            |   |
| Balance, beginning of period                                                                                                                   |            | 6 |
| Corporate and other bonds                                                                                                                      |            |   |
| **Allowance for credit losses:**                                                                                                               |            |   |
| Balance, beginning of period                                                                                                                   | 23              | 0 |
| **Additions to the allowance for credit losses:**                                                                                              |            |   |
| Securities for which credit losses were not previously recorded                                                                                | 14              | 67 |
| Available-for-sale securities accounted for as PCD assets                                                                                      | 5               | 5 |
| **Reductions to the allowance for credit losses:**                                                                                             |            |   |
| Securities sold during the period (realized)                                                                                                   | 7               | 22 |
| Intent to sell or more likely than not will be required to sell the security before recovery of its amortized cost basis                       | 0               | 1 |
| Write-offs charged against the allowance                                                                                                       | 16              | 0 |
| Recoveries of amounts previously written off                                                                                                   | 0               | 0 |
| Additional increases or (decreases) to the allowance for credit losses on securities that had an allowance recorded in a previous period       | (8)             | (32) |
| Balance, end of period                                                                                                                         | 11              | 23 |
| Corporate and other bonds | Impact of adopting ASC 326                                                                                         |            |   |
| **Allowance for credit losses:**                                                                                                               |            |   |
| Balance, beginning of period                                                                                                                   |            | 6 |
| Asset-backed                                                                                                                                   |            |   |
| **Allowance for credit losses:**                                                                                                               |            |   |
| Balance, beginning of period                                                                                                                   | 17              | 0 |
| **Additions to the allowance for credit losses:**                                                                                              |            |   |
| Securities for which credit losses were not previously recorded                                                                                | 0               | 12 |
| Available-for-sale securities accounted for as PCD assets                                                                                      | 6               | 0 |
| **Reductions to the allowance for credit losses:**                                                                                             |            |   |
| Securities sold during the period (realized)                                                                                                   | 17              | 0 |
| Intent to sell or more likely than not will be required to sell the security before recovery of its amortized cost basis                       | 0               | 0 |
| Write-offs charged against the allowance                                                                                                       | 0               | 0 |
| Recoveries of amounts previously written off                                                                                                   | 0               | 0 |
| Additional increases or (decreases) to the allowance for credit losses on securities that had an allowance recorded in a previous period       | 1               | 5 |
| Balance, end of period                                                                                                                         | $ 7             | 17 |
| Asset-backed | Impact of adopting ASC 326                                                                                                      |            |   |
| **Allowance for credit losses:**                                                                                                               |            |   |
| Balance, beginning of period                                                                                                                   |            | $ 0 |

| X                                                                                                                                                                                                                                                                   |
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| - Definition
Additions To Allowance For Credit Losses
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| - Definition
Amount of expense for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), for which no credit loss was previously recorded.
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922900-210455
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| - Definition
Amount of expense (reversal of expense) for allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), not intended to be sold and not more likely than not will be required to sell before recovery of amortized cost basis, with previously recorded allowance.
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| - Definition
Amount of increase in allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and beneficial interest, purchased with credit deterioration.
+ References
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| - Definition
Amount of increase in allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), from recovery.
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| - Definition
A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
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| - Definition
Amount of decrease in allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) from sale.
+ References
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| - Definition
Amount of decrease in allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) from intent to sell or more likely than not will be required to sell before recovery of amortized cost basis.
+ References
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| - Definition
Amount of writeoff of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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| - Definition
Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).
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