Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2022	Mar. 31, 2021
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 15	$ 19
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	[1],[2]	894
Loss payments for cases		(326)
Accretion of claim liability discount		3
Changes in discount rates		(22)
Changes in assumptions		336
Changes in unearned premium revenue		1
Gross loss and LAE reserve, ending balance	[1],[2]	$ 886

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

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