Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cash and Cash Equivalents, Fair Value Disclosure	$ 1,003	$ 900
Finance receivable	100	95
Loss and loss expense reserves	2,980	2,915
Life Policy Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Finance receivable	31	33
Investment contract reserves:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loss and loss expense reserves	1,589	1,562
Investment contract reserves: | Deferred annuities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loss and loss expense reserves	769	761
Investment contract reserves: | Structured Settlement Annuity
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Loss and loss expense reserves	$ 141	$ 145