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