| **Investments**            | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           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| **Investments [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  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| Investments                | Note B. InvestmentsThe significant components of net investment income are presented in the following table.Net Investment IncomeYears ended December 31     (In millions)2014 2013 2012Fixed maturity securities$1,803 $1,827 $1,846Short term investments3 3 5Limited partnership investments263 451 251Equity securities12 12 12Mortgage loans31 23 17Trading portfolio10 17 24Other3 2 7Gross investment income2,125 2,335 2,162Investment expense(58) (53) (52)Net investment income$2,067 $2,282 $2,110As of December 31, 2014 and 2013, the Company held no non-income producing fixed maturity securities.  As of December 31, 2014 and 2013, no investments in a single issuer exceeded 10% of stockholders' equity, other than investments in securities issued by the U.S. Treasury and obligations of government-sponsored enterprises.Net realized investment gains (losses) are presented in the following table.Net Realized Investment Gains (Losses)Years ended December 31     (In millions)2014 2013 2012Net realized investment gains (losses):     Fixed maturity securities:     Gross realized gains$170 $185 $222Gross realized losses(129) (144) (145)Net realized investment gains (losses) on fixed maturity securities41 41 77Equity securities:     Gross realized gains8 13 19Gross realized losses(7) (35) (42)Net realized investment gains (losses) on equity securities1 (22) (23)Derivatives(1) (9) (2)Short term investments and other16 10 2Net realized investment gains (losses)$57 $20 $54Net change in unrealized gains on investments is presented in the following table.Net Change in Unrealized GainsYears ended December 31     (In millions)2014 2013 2012Net change in unrealized gains on investments:     Fixed maturity securities$1,511 $(2,541) $1,871Equity securities6 (15) 5Other— — (1)Total net change in unrealized gains on investments$1,517 $(2,556) $1,875The components of OTTI losses recognized in earnings by asset type are summarized in the following table.Years ended December 31     (In millions)2014 2013 2012Fixed maturity securities available-for-sale:     Corporate and other bonds$18 $20 $25States, municipalities and political subdivisions46 — 34Asset-backed:     Residential mortgage-backed5 19 48Other asset-backed1 2 —Total asset-backed6 21 48U.S. Treasury and obligations of government-sponsored enterprises— — 1Total fixed maturity securities available-for-sale70 41 108Equity securities available-for-sale:     Common stock7 8 6Preferred stock— 26 36Total equity securities available-for-sale7 34 42Short term investments— 1 —OTTI losses recognized in earnings$77 $76 $150The following tables provide a summary of fixed maturity and equity securities.Summary of Fixed Maturity and Equity SecuritiesDecember 31, 2014Cost orAmortizedCost GrossUnrealizedGains GrossUnrealizedLosses EstimatedFairValue UnrealizedOTTILosses (Gains)(In millions)    Fixed maturity securities available-for-sale:         Corporate and other bonds$17,210 $1,721 $61 $18,870 $—States, municipalities and political subdivisions11,285 1,463 8 12,740 —Asset-backed:         Residential mortgage-backed5,028 218 13 5,233 (53)Commercial mortgage-backed2,056 93 5 2,144 (2)Other asset-backed1,234 11 10 1,235 —Total asset-backed8,318 322 28 8,612 (55)U.S. Treasury and obligations of government-sponsored enterprises26 5 — 31 —Foreign government438 16 — 454 —Redeemable preferred stock39 3 — 42 —Total fixed maturity securities available-for-sale37,316 3,530 97 40,749 $(55)Total fixed maturity securities trading19   19  Equity securities available-for-sale:         Common stock38 9 — 47  Preferred stock172 5 2 175  Total equity securities available-for-sale210 14 2 222  Total$37,545 $3,544 $99 $40,990  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  The following tables summarize the estimated fair value and gross unrealized losses of available-for-sale fixed maturity and equity securities in a gross unrealized loss position by the length of time in which the securities have continuously been in that position.Securities in a Gross Unrealized Loss Position Less than 12 Months 12 Months or Longer TotalDecember 31, 2014EstimatedFair Value GrossUnrealizedLosses EstimatedFair Value GrossUnrealizedLosses EstimatedFair Value GrossUnrealizedLosses(In millions)     Fixed maturity securities available-for-sale:           Corporate and other bonds$1,330 $46 $277 $15 $1,607 $61States, municipalities and political subdivisions335 5 127 3 462 8Asset-backed:           Residential mortgage-backed293 5 189 8 482 13Commercial mortgage-backed264 2 99 3 363 5Other asset-backed607 10 7 — 614 10Total asset-backed1,164 17 295 11 1,459 28U.S. Treasury and obligations of government-sponsored enterprises3 — 4 — 7 —Foreign government3 — 3 — 6 —Redeemable preferred stock3 — — — 3 —Total fixed maturity securities available-for-sale2,838 68 706 29 3,544 97Equity securities available-for-sale:           Preferred stock17 2 1 — 18 2Total$2,855 $70 $707 $29 $3,562 $99 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 1   Foreign 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 $532Based on current facts and circumstances, the Company believes the unrealized losses presented in the December 31, 2014 Securities in a Gross Unrealized Loss Position table above, are not indicative of the ultimate collectibility of the current amortized cost of the securities, but rather are primarily attributable to changes in interest rates and credit spreads, market illiquidity and other factors.  The Company has no current intent to sell securities with unrealized losses, nor is it more likely than not that it will be required to sell prior to recovery of amortized cost; accordingly, the Company has determined that there are no additional OTTI losses to be recorded at December 31, 2014.The following table summarizes the activity for the years ended December 31, 2014, 2013 and 2012 related to the pretax credit loss component reflected in Retained earnings on fixed maturity securities still held at December 31, 2014, 2013 and 2012 for which a portion of an OTTI loss was recognized in Other comprehensive income.Years ended December 31     (In millions)2014 2013 2012Beginning balance of credit losses on fixed maturity securities$74 $95 $92Additional credit losses for securities for which an OTTI loss was previously recognized— 2 23Credit losses for securities for which an OTTI loss was not previously recognized— — 2Reductions for securities sold during the period(9) (23) (14)Reductions for securities the Company intends to sell or more likely than not will be required to sell(3) — (8)Ending balance of credit losses on fixed maturity securities$62 $74 $95Contractual MaturityThe following table summarizes available-for-sale fixed maturity securities by contractual maturity.  Actual maturities may differ from contractual maturities because certain securities may be called or prepaid with or without call or prepayment penalties.  Securities not due at a single date are allocated based on weighted average life.Contractual MaturityDecember 312014 2013(In millions)Cost orAmortizedCost EstimatedFairValue Cost orAmortizedCost EstimatedFairValueDue in one year or less$2,479 $2,511 $2,420 $2,455Due after one year through five years9,054 9,605 9,496 10,068Due after five years through ten years12,055 12,584 11,667 11,954Due after ten years13,728 16,049 15,692 16,720Total$37,316 $40,749 $39,275 $41,197Limited PartnershipsThe carrying value of limited partnerships as of December 31, 2014 and 2013 was $2,937 million and $2,720 million, which includes undistributed earnings of $1,040 million and $969 million.  Limited partnerships comprising 65% of the total carrying value are reported on a current basis through December 31, 2014 with no reporting lag, 16% are reported on a one month lag and the remainder are reported on more than a one month lag.  As of December 31, 2014 and 2013, the Company had 86 and 87 active limited partnership investments.  The number of limited partnerships held and the strategies employed provide diversification to the limited partnership portfolio and the overall invested asset portfolio.Of the limited partnerships held, 73% and 74% at December 31, 2014 and 2013 employ hedge fund strategies that generate returns through investing in marketable securities in the public fixed income and equity markets.  Limited partnerships representing 23% and 22% at December 31, 2014 and 2013 were invested in private debt and equity, and the remaining limited partnerships were primarily invested in real estate strategies.  Hedge fund strategies include both long and short positions in fixed income, equity and derivative instruments.  These hedge fund strategies may seek to generate gains from mispriced or undervalued securities, price differentials between securities, distressed investments, sector rotation or various arbitrage disciplines.  Within hedge fund strategies, approximately 56% were equity related, 27% pursued a multi-strategy approach, 14% were focused on distressed investments and 3% were fixed income related at December 31, 2014.The ten largest limited partnership positions held totaled $1,492 million and $1,471 million as of December 31, 2014 and 2013.  Based on the most recent information available regarding the Company’s percentage ownership of the individual limited partnerships, the carrying value reflected on the Consolidated Balance Sheets represents approximately 4% of the aggregate partnership equity at December 31, 2014 and 2013, and the related income reflected on the Consolidated Statements of Operations represents approximately 4%, 4% and 3% of the changes in total partnership equity for the years ended December 31, 2014, 2013 and 2012.While the Company generally does not invest in highly leveraged partnerships, there are risks which may result in losses due to short-selling, derivatives or other speculative investment practices.  The use of leverage increases volatility generated by the underlying investment strategies.The Company’s limited partnership investments contain withdrawal provisions that generally limit liquidity for a period of thirty days up to one year and in some cases do not permit withdrawals until the termination of the partnership.  Typically, withdrawals require advance written notice of up to 90 days.Commercial Mortgage LoansRisks related to the recoverability of loan balances include declines in the estimated cash flows from underlying property leases, fair value of collateral and creditworthiness of tenants of credit tenant loan properties, where lease payments directly service the loan.  The Company evaluates loans for impairment on a specific loan basis and identifies loans for evaluation of impairment based on the collection experience of each loan and other credit quality indicators such as debt service coverage ratio and the creditworthiness of the borrower or tenants of credit tenant loan properties.  As of December 31, 2014 and 2013, there were no loans past due or in non-accrual status, and no valuation allowance was recorded.Investment CommitmentsAs of December 31, 2014, the Company had committed approximately $327 million to future capital calls from various third-party limited partnership investments in exchange for an ownership interest in the related partnerships.As of December 31, 2014, the Company had a mortgage loan commitment of $8 million representing a signed loan application received and accepted.The Company invests in various privately placed debt securities, including bank loans, as part of its overall investment strategy and has committed to additional future purchases, sales and funding.  As of December 31, 2014, the Company had commitments to purchase or fund additional amounts of $75 million and sell $97 million under the terms of such securities.Investments on DepositSecurities with carrying values of approximately $3.0 billion and $3.3 billion were deposited by the Company’s insurance subsidiaries under requirements of regulatory authorities and others as of December 31, 2014 and 2013.Cash and securities with carrying values of approximately $361 million and $353 million were deposited with financial institutions as collateral for letters of credit as of December 31, 2014 and 2013.  In addition, cash and securities were deposited in trusts with financial institutions to secure reinsurance and other obligations with various third parties.  The carrying values of these deposits were approximately $302 million and $294 million as of December 31, 2014 and 2013. |

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| - Definition
The entire disclosure for  investments in certain debt and equity securities.
+ References
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