Business Segments (Summary Of Company's Segment Results) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 616	[1]	$ 644	[1]	$ 880	[1]
Net change in fair value of insured derivatives	459		232		1,464
Net gains (losses) on financial instruments at fair value and foreign exchange	78		69		55
Net investment losses related to other-than-temporary impairments	(15)				(105)
Net gains (losses) on extinguishment of debt	3		60
Other net realized gains (losses)	28		(29)		7
Revenues of consolidated VIEs	101		233		134
Inter-segment revenues	0	[2]	0	[2]	0	[3]
Total revenues	1,270		1,209		2,435
Losses and loss adjustment	133		117		50
Operating	239		384		431
Interest	210		236		284
Expenses of consolidated VIEs	47		56		72
Inter-segment expenses	0	[2]	0	[2]	0	[3]
Total expenses	629		793		837
Income (loss) before income taxes	641		416		1,598
Provision (benefit) for income taxes	72		166		364
Net income (loss)	569		250		1,234
Identifiable assets	16,284		16,953		21,724
U S Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Losses and loss adjustment	(10)
Operating Segments [Member] | U S Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	373	[1]	425	[1]	548	[1]
Net change in fair value of insured derivatives	1		3		1
Net gains (losses) on financial instruments at fair value and foreign exchange	26		29		121
Net investment losses related to other-than-temporary impairments	(15)
Other net realized gains (losses)	14		(29)
Inter-segment revenues	44	[2]	90	[2]	168	[3]
Total revenues	443		518		838
Losses and loss adjustment	(10)		105		21
Operating	38		66		124
Inter-segment expenses	78	[2]	96	[2]	124	[3]
Total expenses	106		267		269
Income (loss) before income taxes	337		251		569
Provision (benefit) for income taxes	115		82		188
Net income (loss)	222		169		381
Identifiable assets	5,887		6,056		6,887
Operating Segments [Member] | International And Structured Finance Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	189	[1]	148	[1]	243	[1]
Net change in fair value of insured derivatives	458		229		1,463
Net gains (losses) on financial instruments at fair value and foreign exchange	0		24		93
Net investment losses related to other-than-temporary impairments					(45)
Other net realized gains (losses)	12				1
Revenues of consolidated VIEs	105		237		71
Inter-segment revenues	55	[2]	78	[2]	45	[3]
Total revenues	819		716		1,871
Losses and loss adjustment	143		12		29
Operating	72		108		147
Interest	109		112		132
Expenses of consolidated VIEs	47		50		59
Inter-segment expenses	64	[2]	136	[2]	208	[3]
Total expenses	435		418		575
Income (loss) before income taxes	384		298		1,296
Provision (benefit) for income taxes	134		101		432
Net income (loss)	250		197		864
Identifiable assets	10,086		11,687		17,248
Operating Segments [Member] | Corporate Operations [Member]
Segment Reporting Information [Line Items]
Revenues	42	[1]	55	[1]	68
Net gains (losses) on financial instruments at fair value and foreign exchange	55		15		(158)
Net investment losses related to other-than-temporary impairments					(60)
Net gains (losses) on extinguishment of debt	3		22
Other net realized gains (losses)	2				6
Revenues of consolidated VIEs			(14)
Inter-segment revenues	46	[3]	85	[3]	177
Total revenues	148		163		33
Operating	87		157		114
Interest	101		124		152
Inter-segment expenses	15	[3]	7	[3]	15
Total expenses	203		288		281
Income (loss) before income taxes	(55)		(125)		(248)
Provision (benefit) for income taxes	(173)		(15)		(179)
Net income (loss)	118		(110)		(69)
Identifiable assets	2,846		2,641		2,721
Operating Segments [Member] | Advisory Services [Member]
Segment Reporting Information [Line Items]
Revenues	12	[1]	16	[1]	21
Net gains (losses) on financial instruments at fair value and foreign exchange	(3)		1		(1)
Revenues of consolidated VIEs	(8)
Inter-segment revenues	22	[3]	26	[3]	34
Total revenues	23		43		54
Operating	42		53		46
Inter-segment expenses	6	[3]	7	[3]	13
Total expenses	48		60		59
Income (loss) before income taxes	(25)		(17)		(5)
Provision (benefit) for income taxes	(6)		(5)		(1)
Net income (loss)	(19)		(12)		(4)
Identifiable assets	793		44		44
Operating Segments [Member] | Conduit [Member]
Segment Reporting Information [Line Items]
Revenues	0	[1]	0	[1]
Net gains (losses) on financial instruments at fair value and foreign exchange	0
Net gains (losses) on extinguishment of debt	0
Revenues of consolidated VIEs	4		10		63
Inter-segment revenues	(1)	[2]	(9)	[2]	(2)	[3]
Total revenues	3		1		61
Operating	0
Interest	0
Expenses of consolidated VIEs			6		13
Inter-segment expenses	9	[2]	26	[2]	97	[3]
Total expenses	9		32		110
Income (loss) before income taxes	(6)		(31)		(49)
Provision (benefit) for income taxes	0		(10)		(17)
Net income (loss)	(6)		(21)		(32)
Identifiable assets	0		177		694
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Net gains (losses) on extinguishment of debt			38	[4]
Inter-segment revenues	(166)	[2]	(270)	[2]	(422)	[3]
Total revenues	(166)		(232)		(422)
Inter-segment expenses	(172)	[2]	(272)	[2]	(457)	[3]
Total expenses	(172)		(272)		(457)
Income (loss) before income taxes	6		40		35
Provision (benefit) for income taxes	2		13		(59)
Net income (loss)	4		27		94
Identifiable assets	$ (3,328)	[5]	$ (3,652)	[5]	$ (5,870)	[6]

[1] Represents the sum of third-party financial guarantee net premiums earned, net investment income, insurance-related fees and reimbursements, investment management fees and other fees.

[2] Represents intercompany premium income and expense, intercompany asset management fees and expenses, intercompany interest income and expense pertaining to intercompany receivables and payables and intercompany loans.

[3] Represents intercompany premium income and expense, intercompany asset management fees and expenses, and intercompany interest income and expense pertaining to intercompany receivables and payables.

[4] Represents the gain on the debt received as consideration in connection with the settlement with Bank of America.

[5] Consists of intercompany reinsurance balances, repurchase agreements and deferred income taxes.

[6] Consists of intercompany reinsurance balances, repurchase agreements and loans.