Loss and Loss Adjustment Expense Reserves (Schedule of Loss and Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023		Dec. 31, 2022		Dec. 31, 2021
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue	$ 34		$ 56		$ 83
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	439	[1]	894
Loss payments for cases	(214)		(960)	[2]
Accretion of claim liability discount	15		21
Changes in discount rates	(4)		(102)
Changes in assumptions	235	[3]	570	[4]
Changes in unearned premium revenue	2		16
Gross loss and LAE reserve, ending balance	$ 473	[1]	$ 439	[1]	$ 894

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

[2] Amount is net of recoveries received.

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

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