Fair Value Measurements - Fair Value of Life Policy Loans, Deferred Annuities, and Structured Settlements (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of life policy loans	$ 43	$ 40
Liabilities Related to Investment Contracts, Fair Value Disclosure	999	927
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
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
Fair value of life policy loans	0	0
Liabilities Related to Investment Contracts, Fair Value Disclosure	212	185
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of life policy loans	43	40
Liabilities Related to Investment Contracts, Fair Value Disclosure	787	742
Deferred annuities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities Related to Investment Contracts, Fair Value Disclosure	787	742
Deferred annuities | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
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
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
Liabilities Related to Investment Contracts, Fair Value Disclosure	787	742
Structured settlements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities Related to Investment Contracts, Fair Value Disclosure	212	185
Structured settlements | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities Related to Investment Contracts, Fair Value Disclosure	0	0
Structured settlements | Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities Related to Investment Contracts, Fair Value Disclosure	212	185
Structured settlements | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liabilities Related to Investment Contracts, Fair Value Disclosure	$ 0	$ 0