| **Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions**                                                                                                                                                                                                                                                                                                                                                            | 3 Months Ended | 12 Months Ended |
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| **Quarterly Financial Data [Abstract]**                                                                                                                                                                                                                                                                                                                                                                                                                    |           |            |   |   |  |   |  |   |   |  |   |   |  |   |  |   |
| Revenues                                                                                                                                                                                                                                                                                                                                                                                                                                                   | $ 2,390        | $ 2,433         | $ 2,348 | $ 2,195 |  | $ 2,269 |  | $ 2,153 | $ 2,327 |  | $ 2,352 | $ 9,366 |  | $ 9,101 |  | $ 9,692 |
| Net income (loss)                                                                                                                                                                                                                                                                                                                                                                                                                                          | $ 241          | $ 343           | $ 209 | $ 66 | [1] | $ (70) | [2] | $ 178 | $ 138 | [1] | $ 233 | $ 859 | [1] | $ 479 | [1],[2] | $ 691 |
| Basic earnings (loss) per share                                                                                                                                                                                                                                                                                                                                                                                                                            | $ 0.89         | $ 1.27          | $ 0.77 | $ 0.25 |  | $ (0.26) |  | $ 0.66 | $ 0.51 |  | $ 0.86 | $ 3.18 |  | $ 1.77 |  | $ 2.56 |
| Diluted earnings (loss) per share                                                                                                                                                                                                                                                                                                                                                                                                                          | $ 0.89         | $ 1.26          | $ 0.77 | $ 0.24 |  | $ (0.26) |  | $ 0.66 | $ 0.51 |  | $ 0.86 | $ 3.17 |  | $ 1.77 |  | $ 2.55 |
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| [1]Net income (loss) in the first quarter of 2016 and the second quarter of 2015 included a charge related to the application of retroactive reinsurance accounting to adverse reserve development ceded under the 2010 A&EP Loss Portfolio Transfer in our Corporate & Other Non-Core segment.[2]Net income (loss) in the fourth quarter of 2015 included a charge related to recognition of a premium deficiency in our long term care business. |

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| - Definition
The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.
+ References
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| - Definition
The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.
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| - Definition
The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
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| - Definition
Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).
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