Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2021	Jun. 30, 2020
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 33	$ 38
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	[1],[2]	990
Loss payments for cases		(66)
Accretion of claim liability discount		7
Changes in discount rates		(21)
Changes in assumptions		43
Changes in unearned premium revenue		2
Other		(1)
Gross loss and LAE reserve, ending balance	[1],[2]	$ 954

[1] Amounts are net of expected recoveries.

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