Loss And Loss Adjustment Expense Reserves (Schedule Of Loss And Loss Adjustment Expenses Reserves) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	$ 541
Changes in unearned premium revenue	206		$ 263		$ 371
Gross loss and LAE reserve, ending balance	979		541
Loss And Lae Reserves [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Gross loss and LAE reserve, beginning balance	541		516
Loss payments for cases with reserves	(1,069)	[1]	(128)
Accretion of claim liability discount	12		8
Changes in discount rates	15		5
Changes in assumptions	661		78
Changes in unearned premium revenue	(30)		(15)
Changes in LAE	6		14
Other	843	[2]	63	[3]
Gross loss and LAE reserve, ending balance	$ 979		$ 541		$ 516

[1] Includes payments made to satisfy the Zohar II Claim.

[2] Primarily changes in the amount to satisfy the Zohar II Claim.

[3] Primarily changes in amount and timing of collections.