Loss and Loss Adjustment Expense Reserves (Schedule of Loss and Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2022	Sep. 30, 2021
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 35	$ 72
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	[1],[2]	894
Loss and Payments	[1]	(332)
Accretion of claim liability discount		15
Changes in discount rates		(88)
Changes in assumptions		555
Changes in unearned premium revenue		3
Gross loss and LAE reserve, ending balance	[2],[3]	$ 1,047

[1] Amount is net of recoveries received on claims not yet paid.

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

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