Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 19	$ 43
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	[1],[2]	901
Loss payments for cases		(68)
Accretion of claim liability discount		4
Changes in discount rates		(98)
Changes in assumptions		222
Changes in unearned premium revenue		6
Other		(1)
Gross loss and LAE reserve, ending balance	[1],[2]	$ 966

[1] Amounts are net of expected recoveries of unpaid claims.

[2] Amounts are net of expected recoveries.