Loss and Loss Adjustment Expense Reserves (Schedule of Loss and Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2023	Sep. 30, 2022
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 26	$ 35
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	[1]	439
Loss payments for cases		(210)
Accretion of claim liability discount		9
Changes in discount rates		(24)
Changes in assumptions	[2]	234
Changes in unearned premium revenue		2
Gross loss and LAE reserve, ending balance	[1]	$ 450

[1] Amounts are net of estimated recoveries of expected future claims.

[2] Includes changes in amount and timing of estimated payments and recoveries.