Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 83		$ 77		$ 105
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	[2]	990	[1]	901
Loss payments for cases		(302)		(441)
Accretion of claim liability discount		15		11
Changes in discount rates		(40)		(86)
Changes in assumptions		226		606
Changes in unearned premium revenue		5		8
Other				(9)
Gross loss and LAE reserve, ending balance	[2]	$ 894	[1]	$ 990	[1]	$ 901

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

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