| **Non-Insurance Revenues from Contracts with Customers** | 9 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 RevenueNon-insurance warranty revenue is primarily generated from separately-priced service contracts that provide mechanical breakdown and other coverages to vehicle or consumer goods owners.  The warranty contracts generally provide coverage from 1 month to 10 years.  For warranty products where the Company acts as the principal in the transaction, Non-insurance warranty revenues are reported on a gross basis, with amounts billed to customers reported as Non-insurance warranty revenue and commissions paid to agents reported as Non-insurance warranty expense.  Non-insurance warranty revenue is reported net of any premiums related to contractual liability coverage issued by the Company's insurance operations.  Additionally, the Company provides warranty administration services for dealer and manufacturer obligor warranty products, which include limited warranties and guaranteed automobile protection waivers.The Company recognizes Non-insurance warranty revenues over the service period in proportion to the actuarially determined expected claims emergence pattern.  Customers pay in full at the inception of the warranty contract.  A liability for deferred revenue is recorded when cash payments are received or due in advance of the Company's performance.  The deferred revenue balance includes amounts which are refundable on a pro rata basis upon cancellation.The Company had deferred non-insurance warranty revenue balances of $2.9 billion and $3.3 billion reported in Other liabilities as of January 1, 2018 and September 30, 2018.  The increase in the deferred revenue balance for the nine months ended September 30, 2018 was primarily driven by cash payments received or due in advance of satisfying the Company's performance obligations, offset by cancellations and revenues recognized during the period.  For the three and nine months ended September 30, 2018, the Company recognized $200 million and $635 million of revenues that were included in the deferred revenue balance as of January 1, 2018.  For the three and nine months ended September 30, 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 $316 million of the deferred revenue in the remainder of 2018, $891 million in 2019, $718 million in 2020, and $1.4 billion thereafter.Cost to Obtain and Fulfill Non-Insurance Warranty Contracts with CustomersDealers, retailers and agents earn commission for assisting the Company in obtaining non-insurance warranty contracts.  Additionally, the Company utilizes a third-party to perform warranty administrator services for its consumer good warranties.  These costs, which are deferred and recorded as Other assets, are amortized to Non-insurance warranty expense consistent with how the related revenue is recognized.Losses under warranty contracts shall be recognized when it is probable that estimated future costs exceed unrecognized revenue.  The Company evaluates deferred costs for recoverability including consideration of anticipated investment income.  Adjustments to deferred costs, if necessary, are recorded in the current period results of operations.  No adjustments were recorded for the nine months ended September 30, 2018.As of September 30, 2018, capitalized commission costs were $2.4 billion and capitalized administrator service costs were $22 million.  For the three and nine months ended September 30, 2018, the amount of amortization of capitalized costs was $173 million and $494 million and there was no impairment loss related to the costs capitalized. |

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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://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -URI http://asc.fasb.org/topic&trid=49130388Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -URI http://asc.fasb.org/topic&trid=2122369
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