Loss and Loss Adjustment Expense Reserves (Schedule of Loss and Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2023	Mar. 31, 2022
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 9	$ 15
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		(28)
Accretion of claim liability discount		4
Changes in discount rates		11
Changes in assumptions	[2]	(47)
Changes in unearned premium revenue		0
Gross loss and LAE reserve, ending balance	[1]	$ 379

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

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