Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018
Loss And Loss Adjustment Expense Reserves [Line Items]
Changes in unearned premium revenue		$ 88	$ 142
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	[1],[2]	965
Loss payments for cases		(425)
Accretion of claim liability discount		14
Changes in discount rates		(59)
Changes in assumptions		369
Changes in unearned premium revenue		24
Changes in LAE		(23)
Other		(6)
Gross loss and LAE reserve, ending balance	[1],[2]	$ 859

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

[2] Amounts are net of expected recoveries.