| **Non-Insurance Revenues from Contracts with Customers (Narrative) (Details) - USD ($) $ in Millions** | 3 Months Ended | 6 Months Ended |         |
|--------------------------------------------------------------------------------------------------------|----------------|----------------|---------|
||
| **Revenue from Contract with Customer [Abstract]**                                                     |           |           |    |   |   |
| Deferred non-insurance warranty revenue                                                                | $ 3,852        |           | $ 3,852 |   | $ 3,779 |
| Contract with customer, liability, revenue recognized                                                  | $ 278          | $ 246          | $ 564   | $ 511 |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable.
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130531-203044Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=121556615&loc=SL49130532-203044
+ Details**Name:**us-gaap_ContractWithCustomerLiability**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 8 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130549-203045
+ Details**Name:**us-gaap_ContractWithCustomerLiabilityRevenueRecognized**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - References
No definition available.
+ Details**Name:**us-gaap_RevenueFromContractWithCustomerAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |