Business Segments (Summary Of Company's Segment Results) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011		Dec. 31, 2011
Segment Reporting Information [Line Items]
Total revenues	$ 281		$ 1,120		$ 1,703		$ (390)
Total expenses	338		375		944		775
Income (loss) before income taxes	(57)		745		759		(1,165)
Identifiable assets	22,132		29,370		22,132		29,370		26,873
Unrealized gains (losses) on insured derivatives					(1,473)		531
Losses and loss adjustment					330
U.S. Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	43	[1]	21	[1]	123	[1]	56	[1]
Total revenues	214		208		585		537
Inter-segment expenses	32	[1]	31	[1]	91	[1]	84	[1]
Total expenses	50		51		218		124
Income (loss) before income taxes	164		157		367		413
Identifiable assets	7,134		8,015		7,134		8,015
Structured Finance And International Insurance [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	29	[1]	25	[1]	10	[1]	55	[1]
Total revenues	134		914		1,316		(766)
Inter-segment expenses	54	[1]	33	[1]	154	[1]	91	[1]
Total expenses	298		301		734		568
Income (loss) before income taxes	(164)		613		582		(1,334)
Identifiable assets	17,399		21,251		17,399		21,251
Advisory Services [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	8	[1]	5	[1]	26	[1]	24	[1]
Total revenues	13		14		42		46
Inter-segment expenses	3	[1]	1	[1]	10	[1]	4	[1]
Total expenses	15		15		48		52
Income (loss) before income taxes	(2)		(1)		(6)		(6)
Identifiable assets	53		53		53		53
Corporate [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	53	[1]	22	[1]	132	[1]	66	[1]
Total revenues	64		21		163		105
Inter-segment expenses	4	[1]	4	[1]	10	[1]	11	[1]
Total expenses	42		42		122		122
Income (loss) before income taxes	22		(21)		41		(17)
Identifiable assets	843		652		843		652
Wind-Down Operations [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	(1)	[1],[2]	(4)	[1],[2]	(19)	[1],[2]	(12)	[1],[2]
Total revenues	(12)		32		(131)		(125)
Inter-segment expenses	39	[1],[2]	6	[1],[2]	87	[1],[2]	24	[1],[2]
Total expenses	65		41		174		123
Income (loss) before income taxes	(77)		(9)		(305)		(248)
Identifiable assets	2,861		5,556		2,861		5,556
Eliminations [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	(132)	[1]	(69)	[1]	(272)	[1]	(189)	[1]
Total revenues	(132)		(69)		(272)		(187)
Inter-segment expenses	(132)	[1]	(75)	[1]	(352)	[1]	(214)	[1]
Total expenses	(132)		(75)		(352)		(214)
Income (loss) before income taxes			6		80		27
Identifiable assets	(6,158)	[3]	(6,157)	[3]	(6,158)	[3]	(6,157)	[3]
Non Variable Interest Entities [Member]
Segment Reporting Information [Line Items]
Revenues	225	[4]	284	[4]	683	[4]	802	[4]
Realized gains (losses) and other settlements on insured derivatives	12		(53)		(420)		(599)
Unrealized gains (losses) on insured derivatives	(33)		776		1,473		(531)
Net gains (losses) on financial instruments at fair value and foreign exchange	7		13		(18)		(114)
Net investment losses related to other-than-temporary impairments	(8)		(11)		(105)		(44)
Net gains (losses) on extinguishment of debt							26
Other net realized gains (losses)	1		1		7		6
Losses and loss adjustment	171		190		330		204
Operating	80		88		343		277
Interest	69		75		214		225
Non Variable Interest Entities [Member] | U.S. Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	149	[4]	181	[4]	419	[4]	455	[4]
Realized gains (losses) and other settlements on insured derivatives							2
Net gains (losses) on financial instruments at fair value and foreign exchange	22		6		43		24
Losses and loss adjustment	4		10		15		4
Operating	14		10		112		36
Non Variable Interest Entities [Member] | Structured Finance And International Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	59	[4]	72	[4]	194	[4]	253	[4]
Realized gains (losses) and other settlements on insured derivatives	12		(53)		(420)		(601)
Unrealized gains (losses) on insured derivatives	(33)		776		1,473		(531)
Net gains (losses) on financial instruments at fair value and foreign exchange	14		(12)		80		21
Net investment losses related to other-than-temporary impairments	(4)				(45)		(4)
Other net realized gains (losses)			1		1		2
Losses and loss adjustment	167		180		315		200
Operating	29		38		120		124
Interest	33		33		99		99
Non Variable Interest Entities [Member] | Advisory Services [Member]
Segment Reporting Information [Line Items]
Revenues	5	[4]	9	[4]	16	[4]	22	[4]
Operating	12		14		38		48
Non Variable Interest Entities [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	3	[4]	1	[4]	10	[4]	2	[4]
Net gains (losses) on financial instruments at fair value and foreign exchange	11		8		19		47
Net investment losses related to other-than-temporary impairments	(4)		(10)		(4)		(10)
Other net realized gains (losses)	1				6
Operating	24		24		69		67
Interest	14		14		43		44
Non Variable Interest Entities [Member] | Wind-Down Operations [Member]
Segment Reporting Information [Line Items]
Revenues	9	[4],[5]	21	[4],[5]	44	[4],[5]	70	[4],[5]
Net gains (losses) on financial instruments at fair value and foreign exchange	(40)		11		(160)		(206)
Net investment losses related to other-than-temporary impairments			(1)		(56)		(30)
Net gains (losses) on extinguishment of debt							24
Other net realized gains (losses)							4
Operating	1		2		4		2
Interest	22		28		72		82
Non Variable Interest Entities [Member] | Eliminations [Member]
Segment Reporting Information [Line Items]
Net gains (losses) on extinguishment of debt							2
Variable Interest Entity [Member]
Segment Reporting Information [Line Items]
Identifiable assets	8,200				8,200				10,900
Net gains (losses) on financial instruments at fair value and foreign exchange	44		88		(17)		3
Net gains (losses) on extinguishment of debt	16				49
Other net realized gains (losses)			5				8
Revenues of consolidated VIEs	77		110		83		64
Interest	13		15		43		45
Expenses of consolidated VIEs	18		22		57		69
Variable Interest Entity [Member] | Structured Finance And International Insurance [Member]
Segment Reporting Information [Line Items]
Revenues of consolidated VIEs	57		105		23		39
Expenses of consolidated VIEs	15		17		46		54
Variable Interest Entity [Member] | Wind-Down Operations [Member]
Segment Reporting Information [Line Items]
Revenues of consolidated VIEs	20		5		60		25
Expenses of consolidated VIEs	$ 3		$ 5		$ 11		$ 15

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

[2] Represents intercompany asset management fees and expenses plus intercompany interest income and expense pertaining to intercompany debt.

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

[4] 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.

[5] Represents the sum of third-party interest income, investment management services fees and other fees.