Income Taxes (Components Of Deferred Tax Assets and Liabilities) (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Deferred tax liabilities:
Unearned premium reserve	$ 48	$ 54
Deferred acquisition costs	10	13
Net unrealized gains and losses in accumulated other comprehensive income	25	0
Net deferred taxes on VIEs	53	51
Other	6	0
Total gross deferred tax liabilities	142	118
Deferred tax assets:
Compensation and employee benefits	9	8
Accrued interest	210	185
Partnership basis difference	10	10
Loss and loss adjustment expense reserves	98	101
Net operating loss	656	590
Foreign tax credits	61	61
Other-than-temporary impairments	0	2
Net unrealized losses on insured derivatives	10	9
Net gains and losses on financial instruments at fair value and foreign exchange	54	21
Other		4
Total gross deferred tax assets	1,108	991
Valuation allowance	966	873
Net deferred tax asset	$ 0	$ 0