| **Deferred Acquisition Costs  (Tables)**                                                                              | 9 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|-----------------------------------------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Deferred Costs [Abstract]**                                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
| Deferred Policy Acquisition Costs And Asset Reconciliation, Including the Amortized Deferred Policy Acquisition Costs | The table below shows the deferred policy acquisition costs and asset reconciliation.(Dollars in millions)Three months ended September 30, Nine months ended September 30,2016 2015 2016 2015Property casualty:       Deferred policy acquisition costs asset, beginning of period$412 $390 $388 $379Capitalized deferred policy acquisition costs216 201 644 606Amortized deferred policy acquisition costs(207) (197) (611) (591)Deferred policy acquisition costs asset, end of period$421 $394 $421 $394        Life:       Deferred policy acquisition costs asset, beginning of period$212 $210 $228 $199Capitalized deferred policy acquisition costs11 11 35 34Amortized deferred policy acquisition costs(15) (10) (37) (29)Amortized shadow deferred policy acquisition costs(2) 4 (20) 11Deferred policy acquisition costs asset, end of period$206 $215 $206 $215        Consolidated:       Deferred policy acquisition costs asset, beginning of period$624 $600 $616 $578Capitalized deferred policy acquisition costs227 212 679 640Amortized deferred policy acquisition costs(222) (207) (648) (620)Amortized shadow deferred policy acquisition costs(2) 4 (20) 11Deferred policy acquisition costs asset, end of period$627 $609 $627 $609         |

| X                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
+ Details**Name:**us-gaap_DeferredCostsAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Tabular disclosure of the movement in deferred policy acquisition costs.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35755530&loc=d3e11264-158415
+ Details**Name:**us-gaap_DeferredPolicyAcquisitionCostsTableTextBlock**Namespace Prefix:**us-gaap_**Data Type:**nonnum:textBlockItemType**Balance Type:**na**Period Type:**duration |