Loss and Loss Adjustment Expense Reserves (Schedule of Loss and Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2024	Mar. 31, 2023
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 8	$ 9
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	[1]	473
Loss payments for cases		(19)
Accretion of claim liability discount		4
Changes in discount rates		(11)
Changes in assumptions	[2]	26
Changes in unearned premium revenue		(3)
Gross loss and LAE reserve, ending balance	[1]	$ 470

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

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