Loss and Loss Adjustment Expense Reserves (Schedule of Loss and Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2022	Jun. 30, 2021
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 25	$ 33
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 LAE		(355)
Accretion of claim liability discount		10
Changes in discount rates		(59)
Changes in assumptions		473
Changes in unearned premium revenue		2
Gross loss and LAE reserve, ending balance	[1],[2]	$ 965

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

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