| **Non-Insurance Revenues from Contracts with Customers** | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
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| **Revenue from Contract with Customer [Abstract]**       |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
| Non-Insurance Revenues from Contracts with Customers     | Non-Insurance Revenues from Contracts with CustomersNon-Insurance revenue is recognized when obligations under the terms of a contract with a customer are satisfied; generally this occurs over time as obligations are fulfilled.  Revenue is measured as the amount of consideration the Company expects to receive in exchange for providing services.Deferred Non-Insurance Warranty RevenueThe Company had deferred non-insurance warranty revenue balances of $3.8 billion and $3.4 billion reported in Deferred non-insurance warranty revenue as of December 31, 2019 and 2018.  The increase in the deferred revenue balance for the year ended December 31, 2019 was primarily driven by deferrals outpacing revenue recognized in the period due to growth in the business.  For the year ended December 31, 2019, the Company recognized $971 million of revenues that were included in the deferred revenue balance as of January 1, 2019.  For the year ended December 31, 2018, the Company recognized $834 million of revenues that were included in the deferred revenue balance as of January 1, 2018.  For the years ended December 31, 2019 and 2018, Non-insurance warranty revenue recognized from performance obligations related to prior periods due to a change in estimate was not material.  The Company expects to recognize approximately $1.1 billion of the deferred revenue in 2020, $882 million in 2021, $674 million in 2022 and $1.1 billion thereafter.Cost to Obtain and Fulfill Non-Insurance Warranty Contracts with CustomersFor the years ended December 31, 2019 and 2018, capitalized commission costs were $2.8 billion and $2.5 billion and capitalized administrator service costs were $31 million and $24 million.  For the years ended December 31, 2019 and 2018, the amount of amortization of capitalized costs were $813 million and $673 million and there were no impairment losses related to the costs capitalized.  There were no adjustments to deferred costs recorded for the years ended December 31, 2019 and 2018. |

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| - References
No definition available.
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| - Definition
The entire disclosure of revenue from contract with customer to transfer good or service and to transfer nonfinancial asset. Includes, but is not limited to, disaggregation of revenue, credit loss recognized from contract with customer, judgment and change in judgment related to contract with customer, and asset recognized from cost incurred to obtain or fulfill contract with customer. Excludes insurance and lease contracts.
+ References
Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -URI http://asc.fasb.org/topic&trid=49130388
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