| **Investments (Narrative) (Details) - USD ($)**                                                                   | 12 Months Ended |
|-------------------------------------------------------------------------------------------------------------------|-----------------|
||
| **Gain (Loss) on Securities [Line Items]**                                                                        |            |   |   |
| Non-income producing fixed maturity securities                                                                    | $ 0             | $ 0 |   |
| Investments that exceed ten percent of stockholders' equity                                                       | 0               | 0 |   |
| Investment and derivative, realized gain (loss), coinsurance agreement                                            |            |   | $ 18,000,000 |
| Gross gains                                                                                                       | 48,000,000      | 75,000,000 | 120,000,000 |
| Debt securities, available-for-sale, realized loss                                                                | 150,000,000     | 166,000,000 | 261,000,000 |
| Mortgage loan losses due to changes in expected credit losses                                                     | 0               | 11,000,000 | $ 8,000,000 |
| Limited partnership investments                                                                                   | 2,520,000,000   | 2,174,000,000 |   |
| Undistributed earnings of limited partnership investments                                                         | $ 334,000,000   | $ 250,000,000 |   |
| Percentage of limited partnerships reported on a current basis                                                    | 14.00%          |   |   |
| Percentage of limited partnerships reported on a one month lag                                                    | 3.00%           |   |   |
| Limited partnerships invested in private debt and equity                                                          | 86.00%          | 85.00% |   |
| Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments | 14.00%          | 15.00% |   |
| Carrying value of ten largest limited partnerships                                                                | $ 648,000,000   | $ 622,000,000 |   |
| Carrying value of limited partnerships as percentage of aggregate partnership equity                              | 1.00%           | 1.00% |   |
| Income as percentage of change in partnership equity for all limited partnerships                                 | 1.00%           | 1.00% | 2.00% |
| Obligation to return cash                                                                                         | $ 0             | $ 1,000,000 |   |
| Derivative liability, subject to master netting arrangement, collateral, right to reclaim cash offset             | 0               | 0 |   |
| Commitments to purchase or fund privately placed debt securities                                                  | 1,660,000,000   |   |   |
| Commitments to sell various privately placed debt securities                                                      | 30,000,000      |   |   |
| Carrying value of securities deposited under requirements of regulatory authorities                               | 3,100,000,000   | 3,100,000,000 |   |
| Cash and securities deposited as collateral for letters of credit                                                 | 700,000,000     | 900,000,000 |   |
| Fixed maturity securities                                                                                         |            |   |   |
| **Gain (Loss) on Securities [Line Items]**                                                                        |            |   |   |
| OCI, debt securities, available-for-sale, gain (loss), after adjustment, before tax                               | (352,000,000)   | 1,431,000,000 | $ (7,850,000,000) |
| Debt securities, available-for-sale, accrued interest, after allowance for credit loss                            | 442,000,000     | 435,000,000 |   |
| Mortgage loans                                                                                                    |            |   |   |
| **Gain (Loss) on Securities [Line Items]**                                                                        |            |   |   |
| Financing receivable, accrued interest, after allowance for credit loss                                           | 4,000,000       |   |   |
| Amortized cost of mortgage loans                                                                                  | 48,000,000      |   |   |
| Financing receivable, allowance for credit loss                                                                   | $ 14,000,000    |   |   |
| Non-income producing mortgage loans                                                                               |            | $ 20,000,000 |   |
| Funds Withheld Liability Securities                                                                               |            |   |   |
| **Gain (Loss) on Securities [Line Items]**                                                                        |            |   |   |
| Gross gains                                                                                                       |            |   | 62,000,000 |
| Debt securities, available-for-sale, realized loss                                                                |            |   | $ 44,000,000 |

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Carrying Value Of Ten Largest Limited Partnerships
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Cash And Securities Deposited As Collateral For Letters Of Credit
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Investments that Exceed Ten Percent of Stockholders' Equity, other than investments in U.S. Treasury and U.S. Government agency securities.
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Non-Income Producing Fixed Maturity Securities
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Percentage of limited partnerships employing hedge fund strategies focused on fixed income and equity investments
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Percentage of total carrying value of limited partnerships reported on a current basis
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Percentage of total carrying value of limited partnerships reported on a one month lag.
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Amount, after allowance for credit loss, of accrued interest 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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Amount of realized gain 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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Amount of realized 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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Amount of obligation to return cash collateral under master netting arrangements that have not been offset against derivative assets.
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Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.
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Amount, after allowance for credit loss, of accrued interest on financing receivable.
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Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.
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Amortized cost of financing receivable on nonaccrual status. Excludes net investment in lease.
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Amount of mortgage loan on real estate which is non-income producing for twelve months preceding statement of financial position date.
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Amount, before tax and after adjustment, of unrealized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale) and unrealized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity) from transfer to available-for-sale.
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Amount of credit loss expense (reversal of expense) for financing receivable.
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Amount of consolidated retained earnings that represent undistributed (not yet received) earnings from 50 percent or less owned persons accounted for by the equity method (equity method investees).
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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.
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