| **Accumulated Other Comprehensive Income (Loss) by Component Schedule of Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions** | 3 Months Ended | 9 Months Ended |          |         |        |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|----------|---------|--------|
||
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       |           |           | $ 12,244 |    |   |   |   |
| Other comprehensive income (loss) before reclassifications                                                                                                              | $ (149)        | $ 77           | (770)    | $ 322   |   |   |   |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                      | 3              | 2              | 3        | 42      |   |   |   |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                           | (152)          | 75             | (773)    | 280     |   |   |   |
| Total stockholder's equity at end of period                                                                                                                             | 11,510         | 12,169         | 11,510   | 12,169  |   |   |   |
| Cumulative effect on retained earnings, tax                                                                                                                             |           |           | 8        |    |   |   |   |
| Reclassification from AOCI, tax                                                                                                                                         | (1)            | 1              | (1)      | (17)    |   |   |   |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                              | 41             | (21)           | 194      | (113)   |   |   |   |
| Net unrealized gains (losses) on investments with OTTI losses                                                                                                           |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       | 20             | 26             | 30       | 30      |   |   |   |
| Other comprehensive income (loss) before reclassifications                                                                                                              | (1)            | 1              | (12)     | 0       |   |   |   |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                      | 0              | 0              | (1)      | 3       |   |   |   |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                           | (1)            | 1              | (11)     | (3)     |   |   |   |
| Total stockholder's equity at end of period                                                                                                                             | 19             | 27             | 19       | 27      |   |   |   |
| Cumulative effect on retained earnings, tax                                                                                                                             |           |           | 0        |    |   |   |   |
| Reclassification from AOCI, tax                                                                                                                                         | 0              | 0              | 0        | (1)     |   |   |   |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                              | 0              | 0              | 3        | 1       |   |   |   |
| Net unrealized gains (losses) on other investments                                                                                                                      |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       | 271            | 786            | 859      | 642     |   |   |   |
| Other comprehensive income (loss) before reclassifications                                                                                                              | (148)          | 35             | (718)    | 228     |   |   |   |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                      | 10             | 12             | 28       | 61      |   |   |   |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                           | (158)          | 23             | (746)    | 167     |   |   |   |
| Total stockholder's equity at end of period                                                                                                                             | 113            | 809            | 113      | 809     |   |   |   |
| Cumulative effect on retained earnings, tax                                                                                                                             |           |           | 8        |    |   |   |   |
| Reclassification from AOCI, tax                                                                                                                                         | (2)            | (4)            | (7)      | (28)    |   |   |   |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                              | 42             | (16)           | 197      | (102)   |   |   |   |
| Pension and postretirement benefits                                                                                                                                     |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       | (758)          | (635)          | (775)    | (647)   |   |   |   |
| Other comprehensive income (loss) before reclassifications                                                                                                              | 0              | 0              | 0        | 0       |   |   |   |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                      | (7)            | (10)           | (24)     | (22)    |   |   |   |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                           | 7              | 10             | 24       | 22      |   |   |   |
| Total stockholder's equity at end of period                                                                                                                             | (751)          | (625)          | (751)    | (625)   |   |   |   |
| Cumulative effect on retained earnings, tax                                                                                                                             |           |           | 0        |    |   |   |   |
| Reclassification from AOCI, tax                                                                                                                                         | 1              | 5              | 6        | 12      |   |   |   |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                              | (1)            | (5)            | (6)      | (12)    |   |   |   |
| Cumulative foreign currency translation adjustment                                                                                                                      |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       | (138)          | (145)          | (98)     | (198)   |   |   |   |
| Other comprehensive income (loss) before reclassifications                                                                                                              | 0              | 41             | (40)     | 94      |   |   |   |
| Amounts reclassified from accumulated other comprehensive income (loss) net of tax                                                                                      | 0              | 0              | 0        | 0       |   |   |   |
| Other comprehensive income (loss) after tax (expense) benefit                                                                                                           | 0              | 41             | (40)     | 94      |   |   |   |
| Total stockholder's equity at end of period                                                                                                                             | (138)          | (104)          | (138)    | (104)   |   |   |   |
| Cumulative effect on retained earnings, tax                                                                                                                             |           |           | 0        |    |   |   |   |
| Reclassification from AOCI, tax                                                                                                                                         | 0              | 0              | 0        | 0       |   |   |   |
| Tax (expense) benefit on other comprehensive income (loss)                                                                                                              | 0              | 0              | 0        | 0       |   |   |   |
| Accumulated other comprehensive income (loss)                                                                                                                           |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       | (605)          | 32             | 16       | (173)   |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | $ (16) | $ 0 |
| Total stockholder's equity at end of period                                                                                                                             | $ (757)        | $ 107          | (757)    | 107     |   |   |   |
| ASU 2018-02 | Net unrealized gains (losses) on investments with OTTI losses                                                                                             |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | 5 |   |
| ASU 2018-02 | Net unrealized gains (losses) on other investments                                                                                                        |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | 137 |   |
| ASU 2018-02 | Pension and postretirement benefits                                                                                                                       |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | (130) |   |
| ASU 2018-02 | Cumulative foreign currency translation adjustment                                                                                                        |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | 0 |   |
| ASU 2018-02 | Accumulated other comprehensive income (loss)                                                                                                             |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    | $ 12   | 12 |   |
| ASU 2016-01 | Net unrealized gains (losses) on investments with OTTI losses                                                                                             |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | 0 |   |
| ASU 2016-01 | Net unrealized gains (losses) on other investments                                                                                                        |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | (28) |   |
| ASU 2016-01 | Pension and postretirement benefits                                                                                                                       |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | 0 |   |
| ASU 2016-01 | Cumulative foreign currency translation adjustment                                                                                                        |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | 0 |   |
| ASU 2016-01 | Accumulated other comprehensive income (loss)                                                                                                             |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Cumulative effect adjustments from changes in accounting guidance, net of tax                                                                                           |           |           |     |    |   | $ (28) |   |
| Previously reported | Net unrealized gains (losses) on investments with OTTI losses                                                                                     |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       |           |           | 25       |    |   |   |   |
| Previously reported | Net unrealized gains (losses) on other investments                                                                                                |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       |           |           | 750      |    |   |   |   |
| Previously reported | Pension and postretirement benefits                                                                                                               |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       |           |           | (645)    |    |   |   |   |
| Previously reported | Cumulative foreign currency translation adjustment                                                                                                |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       |           |           | (98)     |    |   |   |   |
| Previously reported | Accumulated other comprehensive income (loss)                                                                                                     |           |           |     |    |   |   |   |
| **AOCI Attributable to Parent, Net of Tax [Roll Forward]**                                                                                                              |           |           |     |    |   |   |   |
| Total stockholder's equity at beginning of period                                                                                                                       |           |           | $ 32     | $ (173) |   |   |   |

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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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Amount after tax of increase (decrease) to equity or (increase) decrease to net assets, resulting from the cumulative effect adjustment of a new accounting principle applied in the period of adoption.
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Amount of the related income tax effect of a cumulative effect on retained earnings.
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Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent.
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| - Definition
Amount after tax of other comprehensive income (loss) attributable to parent entity.
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Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.
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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.
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