| **Property Casualty Loss and Loss Expenses** | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     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| **Premiums Written, Net [Abstract]**         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    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| Property Casualty Loss And Loss Expenses     | Property Casualty Loss and Loss ExpensesThis table summarizes activity for our consolidated property casualty loss and loss expense reserves:(Dollars in millions) Three months ended September 30, Nine months ended September 30,  2015 2014 2015 2014Gross loss and loss expense reserves, beginning  of period $4,647 $4,408 $4,438 $4,241Less reinsurance recoverable 292 282 282 299Net loss and loss expense reserves, beginning of  period 4,355 4,126 4,156 3,942Net incurred loss and loss expenses related to:        Current accident year 661 647 2,096 2,125Prior accident years (48) (25) (140) (120)Total incurred 613 622 1,956 2,005Net paid loss and loss expenses related to:        Current accident year 343 353 794 859Prior accident years 261 286 954 979Total paid 604 639 1,748 1,838Net loss and loss expense reserves, end of period 4,364 4,109 4,364 4,109Plus reinsurance recoverable 289 284 289 284Gross loss and loss expense reserves, end of  period $4,653 $4,393 $4,653 $4,393          We use actuarial methods, models and judgment to estimate, as of a financial statement date, the property casualty loss and loss expense reserves required to pay for and settle all outstanding insured claims, including incurred but not reported (IBNR) claims, as of that date. The actuarial estimate is subject to review and adjustment by an inter-departmental committee that includes actuarial management that is familiar with relevant company and industry business, claims and underwriting trends, as well as general economic and legal trends that could affect future loss and loss expense payments. The amount we will actually have to pay for claims can be highly uncertain. This uncertainty, together with the size of our reserves, makes the loss and loss expense reserves our most significant estimate. The reserve for loss and loss expenses in the condensed consolidated balance sheets also included $47 million at September 30, 2015, and $42 million at September 30, 2014, for certain life and health loss and loss expense reserves.For the three months ended September 30, 2015, we experienced $48 million of favorable development on prior accident years, including $43 million of favorable development in commercial lines, $2 million of adverse development in personal lines and $7 million of favorable development in excess and surplus lines. We recognized favorable reserve development during the three months ended September 30, 2015, of $25 million for the workers' compensation line and $16 million for the commercial casualty line due to reduced uncertainty of prior accident year loss and loss adjustment expense for these lines. Our commercial auto line developed unfavorably by $4 million for the three months ended September 30, 2015, due to higher loss cost effects in recent accident years, resulting in an increase of our reserve estimate for claims that have not yet been settled.For the nine months endedSeptember 30, 2015, we experienced $140 million of favorable development on prior accident years, including $120 million of favorable development in commercial lines, $1 million of adverse development in personal lines and $21 million of favorable development in excess and surplus lines. This included $12 million from favorable development of catastrophe losses for the nine months endedSeptember 30, 2015. We recognized favorable reserve development during the nine months endedSeptember 30, 2015, of $80 million for the workers' compensation line, $36 million for the commercial casualty line and $17 million for the other commercial line due to reduced uncertainty of prior accident year loss and loss adjustment expense for these lines. Our commercial auto line developed unfavorably by $27 million for the nine months ended September 30, 2015, due to higher loss cost effects in recent accident years, resulting in an increase of our reserve estimate for claims that have not yet been settled.For the three months ended September 30, 2014, we experienced $25 million of favorable development on prior accident years, including $24 million of favorable development in commercial lines, $5 million of adverse development in personal lines and $6 million of favorable development in excess and surplus lines. This included $5 million from favorable development of catastrophe losses for the three months ended September 30, 2014. We recognized favorable development during the three months ended September 30, 2014, of $15 million for workers' compensation line, $8 million for each the commercial property line and the commercial casualty line and $12 million of adverse development for the commercial auto line, due to reduced uncertainty of prior accident year loss and loss adjustment expense for these lines.For the nine months endedSeptember 30, 2014, we experienced $120 million of favorable development on prior accident years, including $84 million of favorable development in commercial lines, $13 million of favorable development in personal lines and $23 million of favorable development in excess and surplus lines. This included $19 million from favorable development of catastrophe losses for the nine months endedSeptember 30, 2014. We recognized favorable development during the nine months ended September 30, 2014, of $45 million for the workers' compensation line, $33 million for the commercial property line, $25 million for the commercial casualty line and $24 million of adverse development in the commercial auto line, due to reduced uncertainty of prior accident year loss and loss adjustment expense for these lines. |

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| - Definition
The entire disclosure for liabilities related to future policy benefits and unpaid claims and claim adjustments.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6482852&loc=d3e14931-158439Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14754-158437Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.13(a)(1),(b)) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Article 7
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| - References
No definition available.
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