Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivable	$ 58	$ 62
Loss and loss expense reserves	4,970	4,718
Life Policy Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Finance receivable	30	31
Deferred Annuities And Structured Settlements [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liability for Future Policy Benefits, Individual and Group Annuities and Supplementary Contracts	863	860
Loss and loss expense reserves	$ 173	$ 174
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage Of Level 3 Assets To Total Financial Instruments Measured At Fair Value	1.00%