Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 77		$ 105		$ 165
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	[2]	901	[1]	965
Loss payments for cases		(441)		(431)
Accretion of claim liability discount		11		18
Changes in discount rates		(86)		(54)
Changes in assumptions		606		407
Changes in unearned premium revenue		8		23
Changes in LAE				(26)
Other		(9)		(1)
Gross loss and LAE reserve, ending balance	[2]	$ 990	[1]	$ 901	[1]	$ 965

[1] Amounts are net of expected recoveries.

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