| **Income Taxes - Differences Between Statutory Income Tax Rate and Effective Income Tax Rate (Detail) - USD ($) $ in Millions** | 3 Months Ended | 6 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Increase (decrease) resulting from:**                                                                                         |           |           |   |   |
| Tax at statutory rate                                                                                                           | $ 240          | $ 111          | $ (91) | $ 293 |
| Tax-exempt income from municipal bonds                                                                                          | (5)            | (4)            | (10) | (9) |
| Dividend received exclusion                                                                                                     | (4)            | (4)            | (8) | (8) |
| Other                                                                                                                           | 5              | (1)            | (5) | (2) |
| Total provision (benefit) for income taxes                                                                                      | $ 236          | $ 102          | $ (114) | $ 274 |
| **Increase (decrease) resulting from:**                                                                                         |           |           |   |   |
| Tax at statutory rate                                                                                                           | 21.00%         | 21.00%         | 21.00% | 21.00% |
| Tax-exempt income from municipal bonds                                                                                          | (0.40%)        | (0.80%)        | 2.30% | (0.60%) |
| Dividend received exclusion                                                                                                     | (0.30%)        | (0.80%)        | 1.90% | (0.60%) |
| Other                                                                                                                           | 0.30%          | (0.20%)        | 1.30% | (0.20%) |
| Provision for income taxes                                                                                                      | 20.60%         | 19.20%         | 26.50% | 19.60% |

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Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.
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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deduction for dividend.
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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to income (loss) exempt from income taxes.
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