| **Fair Value Measurements - Fair Value of Life Policy Loans, Deferred Annuities, and Structured Settlements (Detail) - USD ($) $ in Millions** | Sep. 30, 2018 | Dec. 31, 2017 |
|------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Finance receivable                                                                                                                             | $ 69          | $ 61          |
| Fair value of life policy loans                                                                                                                | 40            | 41            |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 954           | 1,044         |
| Quoted prices in active markets for identical assets (Level 1)                                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Fair value of life policy loans                                                                                                                | 0             | 0             |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 0             | 0             |
| Significant other observable inputs (Level 2)                                                                                                  |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Fair value of life policy loans                                                                                                                | 0             | 0             |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 194           | 210           |
| Significant unobservable inputs (Level 3)                                                                                                      |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Fair value of life policy loans                                                                                                                | 40            | 41            |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 760           | 834           |
| Policy Loans [Member]                                                                                                                          |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Finance receivable                                                                                                                             | 32            | 31            |
| Deferred annuities                                                                                                                             |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 760           | 834           |
| Deferred annuities | Quoted prices in active markets for identical assets (Level 1)                                                            |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 0             | 0             |
| Deferred annuities | Significant other observable inputs (Level 2)                                                                             |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 0             | 0             |
| Deferred annuities | Significant unobservable inputs (Level 3)                                                                                 |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 760           | 834           |
| Structured Finance [Member]                                                                                                                    |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 194           | 210           |
| Structured Finance [Member] | Quoted prices in active markets for identical assets (Level 1)                                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 0             | 0             |
| Structured Finance [Member] | Significant other observable inputs (Level 2)                                                                    |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | 194           | 210           |
| Structured Finance [Member] | Significant unobservable inputs (Level 3)                                                                        |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**                                               |          |          |
| Liabilities Related to Investment Contracts, Fair Value Disclosure                                                                             | $ 0           | $ 0           |

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
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| - Definition
Fair value portion of liability related to investment contracts for example, but not limited to, guaranteed investment contract or annuities.
+ References
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| - Definition
Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.
+ References
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