| **Investments (Tables)**                                                                                                                                                                   | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
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| **Investments [Abstract]**                                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
| Net investment income                                                                                                                                                                      | Net Investment IncomePeriods ended June 30Three Months Six Months(In millions)2014 2013 2014 2013Fixed maturity securities$451 $454 $903 $911Short term investments— 1 1 2Limited partnership investments97 79 170 210Equity securities3 3 5 6Mortgage loans9 6 15 11Trading portfolio3 5 6 10Other1 — 3 1Gross investment income564 548 1,103 1,151Investment expense(14) (14) (27) (26)Net investment income$550 $534 $1,076 $1,125                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| Net realized investment gains (losses)                                                                                                                                                     | Net Realized Investment Gains (Losses)Periods ended June 30Three Months Six Months(In millions)2014 2013 2014 2013Net realized investment gains (losses):       Fixed maturity securities:       Gross realized gains$20 $33 $73 $72Gross realized losses(39) (40) (54) (52)Net realized investment gains (losses) on fixed maturity securities(19) (7) 19 20Equity securities:       Gross realized gains— 5 5 7Gross realized losses— (7) — (22)Net realized investment gains (losses) on equity securities— (2) 5 (15)Derivatives1 (5) 1 (3)Short term investments and other4 — 7 7Net realized investment gains (losses)$(14) $(14) $32 $9                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| Components of net other-than-temporary impairment losses recognized in continuing earnings                                                                                                 | The components of net other-than-temporary impairment (OTTI) losses recognized in earnings by asset type are summarized in the following table.Periods ended June 30Three Months Six Months(In millions)2014 2013 2014 2013Fixed maturity securities available-for-sale:       Corporate and other bonds$2 $5 $3 $8Asset-backed:       Residential mortgage-backed1 3 2 3Other asset-backed1 1 1 1Total asset-backed2 4 3 4Total fixed maturity securities available-for-sale4 9 6 12Equity securities available-for-sale:       Common stock1 2 1 2Preferred stock— 5 — 20Total equity securities available-for-sale1 7 1 22Net OTTI losses recognized in earnings$5 $16 $7 $34                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| Summary of fixed maturity and equity securities                                                                                                                                            | Summary of Fixed Maturity and Equity SecuritiesJune 30, 2014Cost orAmortizedCost GrossUnrealizedGains GrossUnrealizedLosses EstimatedFairValue UnrealizedOTTILosses (Gains)(In millions)    Fixed maturity securities available-for-sale:         Corporate and other bonds$17,276 $1,852 $30 $19,098 $—States, municipalities and political subdivisions11,215 1,178 70 12,323 —Asset-backed:         Residential mortgage-backed4,882 202 14 5,070 (51)Commercial mortgage-backed1,999 107 7 2,099 (3)Other asset-backed1,172 16 3 1,185 —Total asset-backed8,053 325 24 8,354 (54)U.S. Treasury and obligations of government-sponsored enterprises61 6 1 66 —Foreign government533 18 1 550 —Redeemable preferred stock39 3 — 42 —Total fixed maturity securities available-for-sale37,177 3,382 126 40,433 $(54)Total fixed maturity securities trading35 — — 35  Equity securities available-for-sale:         Common stock46 14 — 60  Preferred stock129 5 — 134  Total equity securities available-for-sale175 19 — 194  Total$37,387 $3,401 $126 $40,662  December 31, 2013Cost orAmortizedCost GrossUnrealizedGains GrossUnrealizedLosses EstimatedFairValue UnrealizedOTTILosses (Gains)(In millions)    Fixed maturity securities available-for-sale:         Corporate and other bonds$19,352 $1,645 $135 $20,862 $—States, municipalities and political subdivisions11,281 548 272 11,557 —Asset-backed:         Residential mortgage-backed4,940 123 92 4,971 (37)Commercial mortgage-backed1,995 90 22 2,063 (3)Other asset-backed945 13 3 955 —Total asset-backed7,880 226 117 7,989 (40)U.S. Treasury and obligations of government-sponsored enterprises139 6 1 144 —Foreign government531 15 3 543 —Redeemable preferred stock92 10 — 102 —Total fixed maturity securities available-for-sale39,275 2,450 528 41,197 $(40)Total fixed maturity securities trading36 — — 36  Equity securities available-for-sale:         Common stock36 9 — 45  Preferred stock143 1 4 140  Total equity securities available-for-sale179 10 4 185  Total$39,490 $2,460 $532 $41,418   |
| Securities in a gross unrealized loss position                                                                                                                                             | Securities in a Gross Unrealized Loss Position Less than 12 Months 12 Months or Longer TotalJune 30, 2014EstimatedFair Value GrossUnrealizedLosses EstimatedFair Value GrossUnrealizedLosses EstimatedFair Value GrossUnrealizedLosses(In millions)     Fixed maturity securities available-for-sale:           Corporate and other bonds$813 $12 $548 $18 $1,361 $30States, municipalities and political subdivisions316 2 587 68 903 70Asset-backed:           Residential mortgage-backed125 1 332 13 457 14Commercial mortgage-backed205 2 171 5 376 7Other asset-backed269 3 12 — 281 3Total asset-backed599 6 515 18 1,114 24U.S. Treasury and obligations of government-sponsored enterprises2 1 4 — 6 1Foreign government39 1 9 — 48 1Total fixed maturity securities available-for-sale1,769 22 1,663 104 3,432 126Equity securities available-for-sale:           Preferred stock10 — 2 — 12 —Total$1,779 $22 $1,665 $104 $3,444 $126 Less than 12 Months 12 Months or Longer TotalDecember 31, 2013EstimatedFair Value GrossUnrealizedLosses EstimatedFair Value GrossUnrealizedLosses EstimatedFair Value GrossUnrealizedLosses(In millions)     Fixed maturity securities available-for-sale:           Corporate and other bonds$3,592 $129 $72 $6 $3,664 $135States, municipalities and political subdivisions3,251 197 129 75 3,380 272Asset-backed:           Residential mortgage-backed1,293 29 343 63 1,636 92Commercial mortgage-backed640 22 — — 640 22Other asset-backed269 3 — — 269 3Total asset-backed2,202 54 343 63 2,545 117U.S. Treasury and obligations of government-sponsored enterprises13 1 — — 13 1Foreign government111 3 — — 111 3Total fixed maturity securities available-for-sale9,169 384 544 144 9,713 528Equity securities available-for-sale:           Preferred stock87 4 — — 87 4Total$9,256 $388 $544 $144 $9,800 $532                                                                                                                                                                                                                                               |
| Activity related to the pretax fixed maturity credit loss component reflected within retained earnings for securities still held for which a portion of an OTTI loss was recognized in OCI | The following table summarizes the activity for the three and six months ended June 30, 2014 and 2013 related to the pretax credit loss component reflected in Retained earnings on fixed maturity securities still held at June 30, 2014 and 2013 for which a portion of an OTTI loss was recognized in Other comprehensive income (loss).Periods ended June 30Three Months Six Months(In millions)2014 2013 2014 2013Beginning balance of credit losses on fixed maturity securities$69 $92 $74 $95Additional credit losses for securities for which an OTTI loss was previously recognized— 1 — 1Reductions for securities sold during the period(3) (4) (5) (7)Reductions for securities the Company intends to sell or more likely than not will be required to sell— — (3) —Ending balance of credit losses on fixed maturity securities$66 $89 $66 $89                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
| Contractual maturity                                                                                                                                                                       | Contractual Maturity June 30, 2014 December 31, 2013(In millions)Cost orAmortizedCost EstimatedFairValue Cost orAmortizedCost EstimatedFairValueDue in one year or less$2,832 $2,883 $2,420 $2,455Due after one year through five years9,251 9,893 9,496 10,068Due after five years through ten years11,206 11,792 11,667 11,954Due after ten years13,888 15,865 15,692 16,720Total$37,177 $40,433 $39,275 $41,197                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |

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Tabular disclosure of investment income derived from investments in debt and equity securities consisting of interest income earned from investments in debt securities and on cash and cash equivalents, dividend income from investments in equity securities, and income or expense derived from the amortization of investment related discounts or premiums, respectively. This table includes realized gains (losses) on trading securities.
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| - Definition
Tabular disclosure of the amount of other than temporary impairment (OTTI) related to credit losses recognized in earnings including: (a) the beginning balance of the amount related to credit losses on debt securities held by the investor at the beginning of the period for which a portion of an OTTI was recognized in other comprehensive income; (b) additions for the amount related to the credit loss for which an OTTI was not previously recognized; (c) reductions for securities sold during the period (realized); (d) reductions for securities for which the amount previously recognized in other comprehensive income was recognized in earnings because the investor intends to sell the security or more likely than not will be required to sell the security before recovery of its amortized cost basis; (e) additional increases to the amount related to the credit loss for which an OTTI was previously recognized when the investor does not intend to sell the security and it is not more likely than not that the investor will be required to sell the security before recovery of its amortized cost basis; (f) reductions for increases in cash flows expected to be collected that are recognized over the remaining life of the security; and (g) the ending balance of the amount related to credit losses on debt securities held by the entity at the end of the period for which a portion of an OTTI was recognized in other comprehensive income.
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For all investments in an unrealized loss position, including those for which other-than-temporary impairments have not been recognized in earnings (including investments for which a portion of an other-than-temporary impairment has been recognized in other comprehensive income), a tabular disclosure of the aggregate related fair value of investments with unrealized losses and the aggregate amount of unrealized losses (that is, the amount by which amortized cost basis exceeds fair value).
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