Loss And Loss Adjustment Expense Reserves (Loss And LAE Activity) (Narrative) (Detail) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Feb. 28, 2021	Jan. 31, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Loss And Loss Adjustment Expense Reserves [Line Items]
Weighted average risk-free rate used to discount claim liability			1.53%
Percentage of voters voted by the deadline			27.00%
Credit Suisse [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Damages Sought Value		$ 604
Damages Paid Value	$ 600
Lae [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Losses and loss adjustment			$ 47	$ 51	$ 29
Loss and loss adjustment expense reserves			$ 38	$ 30
Changes in Loss and LAE Reserves			one-year