Business Segments (Summary Of Company's Segment Results) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues	[1]	$ 148	$ 199	$ 330
Net change in fair value of insured derivatives			6	15
Net gains (losses) on financial instruments at fair value and foreign exchange		40	(86)	(78)
Net investment losses related to other-than-temporary impairments				(67)
Net gains (losses) on extinguishment of debt		30		(1)
Other net realized gains (losses)		(6)	0	4
Revenues of consolidated VIEs		(23)	163	77
Inter-segment revenues	[2]	0	0	0
Total revenues		189	282	280
Losses and loss adjustment		350	530	242
Amortization of deferred acquisition costs and operating		97	97	103
Interest		163	178	201
Expenses of consolidated VIEs		24	55	91
Inter-segment expenses	[2]	0	0	0
Total expenses		634	860	637
Income (loss) before income taxes		(445)	(578)	(357)
Identifiable assets		4,696	5,751
Operating Segments [Member] | US Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	[1]	85	139	263
Net change in fair value of insured derivatives			0	0
Net gains (losses) on financial instruments at fair value and foreign exchange		(2)	2	15
Net investment losses related to other-than-temporary impairments				(67)
Net gains (losses) on extinguishment of debt		0		0
Other net realized gains (losses)		0	(1)	2
Revenues of consolidated VIEs		0	0	21
Inter-segment revenues	[2]	27	28	28
Total revenues		110	168	262
Losses and loss adjustment		227	163	53
Amortization of deferred acquisition costs and operating		17	14	13
Interest		0	0	0
Expenses of consolidated VIEs		0	0	0
Inter-segment expenses	[2]	45	45	52
Total expenses		289	222	118
Income (loss) before income taxes		(179)	(54)	144
Identifiable assets		3,313	3,644
Operating Segments [Member] | Corporate Operations [Member]
Segment Reporting Information [Line Items]
Revenues	[1]	20	31	32
Net change in fair value of insured derivatives			0	0
Net gains (losses) on financial instruments at fair value and foreign exchange		56	(74)	(59)
Net investment losses related to other-than-temporary impairments				0
Net gains (losses) on extinguishment of debt		30		(1)
Other net realized gains (losses)		(7)	0	(2)
Revenues of consolidated VIEs		0	0	1
Inter-segment revenues	[2]	67	66	62
Total revenues		166	23	33
Losses and loss adjustment		0	0	0
Amortization of deferred acquisition costs and operating		71	69	69
Interest		56	65	73
Expenses of consolidated VIEs		0	0	0
Inter-segment expenses	[2]	22	22	23
Total expenses		149	156	165
Income (loss) before income taxes		17	(133)	(132)
Identifiable assets		873	954
Operating Segments [Member] | International And Structured Finance Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	[1]	43	29	35
Net change in fair value of insured derivatives			6	15
Net gains (losses) on financial instruments at fair value and foreign exchange		(14)	(14)	(34)
Net investment losses related to other-than-temporary impairments				0
Net gains (losses) on extinguishment of debt		0		0
Other net realized gains (losses)		1	1	4
Revenues of consolidated VIEs		(23)	163	55
Inter-segment revenues	[2]	12	12	21
Total revenues		19	197	96
Losses and loss adjustment		123	367	189
Amortization of deferred acquisition costs and operating		9	14	21
Interest		107	113	128
Expenses of consolidated VIEs		24	55	91
Inter-segment expenses	[2]	38	39	36
Total expenses		301	588	465
Income (loss) before income taxes		(282)	(391)	(369)
Identifiable assets		2,800	3,671
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	[1]	0	0	0
Net change in fair value of insured derivatives			0	0
Net gains (losses) on financial instruments at fair value and foreign exchange		0	0	0
Net investment losses related to other-than-temporary impairments				0
Net gains (losses) on extinguishment of debt		0		0
Other net realized gains (losses)		0	0	0
Revenues of consolidated VIEs		0	0	0
Inter-segment revenues	[2]	(106)	(106)	(111)
Total revenues		(106)	(106)	(111)
Losses and loss adjustment		0	0	0
Amortization of deferred acquisition costs and operating		0	0	0
Interest		0	0	0
Expenses of consolidated VIEs		0	0	0
Inter-segment expenses	[2]	(105)	(106)	(111)
Total expenses		(105)	(106)	(111)
Income (loss) before income taxes		(1)	0	$ 0
Identifiable assets	[3]	$ (2,290)	$ (2,518)

[1] Consists of net premiums earned, net investment income, net realized investment gains (losses), insurance-related fees and reimbursements and other fees.

[2] Primarily represents intercompany service charges and intercompany net investment income and expense.

[3] Consists principally of intercompany reinsurance balances.