Loss and Loss Adjustment Expense Reserves (Schedule of Loss and Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2022		Dec. 31, 2021		Dec. 31, 2020
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 56		$ 83		$ 77
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance		894	[1]	990
Loss payments for cases				(302)
Loss and Payments	[2]	(960)
Accretion of claim liability discount		21		15
Changes in discount rates		(102)		(40)
Changes in assumptions	[3]	570		226
Changes in unearned premium revenue		16		5
Gross loss and LAE reserve, ending balance		$ 439	[1]	$ 894	[1]	$ 990

[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.