Business Segments (Summary Of Company's Segment Results) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011		Dec. 31, 2011
Segment Reporting Information [Line Items]
Unrealized gains (losses) on insured derivatives					$ (1,506)		$ 1,307
Total revenues	1,039		98		1,422		(1,510)
Loss and loss adjustment expense					159
Total expenses	244		245		606		400
Income (loss) before income taxes	795		(147)		816		(1,910)
Identifiable assets	22,295				22,295				26,873
U.S. Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	43	[1]	19	[1]	79	[1]	37	[1]
Total revenues	199		177		370		329
Inter-segment expenses	31	[1]	28	[1]	59	[1]	53	[1]
Total expenses	51		33		168		74
Income (loss) before income taxes	148		144		202		255
Structured Finance And International Insurance [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	(11)	[1]	19	[1]	(19)	[1]	29	[1]
Total revenues	843		59		1,182		(1,679)
Inter-segment expenses	54	[1]	30	[1]	100	[1]	59	[1]
Total expenses	198		184		436		267
Income (loss) before income taxes	645		(125)		746		(1,946)
Advisory Services [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	11	[1]	10	[1]	18	[1]	19	[1]
Total revenues	16		17		29		32
Inter-segment expenses	5	[1]	2	[1]	7	[1]	3	[1]
Total expenses	16		20		33		36
Income (loss) before income taxes			(3)		(4)		(4)
Corporate [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	56	[1]	22	[1]	79	[1]	44	[1]
Total revenues	70		38		99		84
Inter-segment expenses	3	[1]	4	[1]	7	[1]	7	[1]
Total expenses	42		39		81		80
Income (loss) before income taxes	28		(1)		18		4
Wind-Down Operations [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	(21)	[1],[2]	(3)	[1],[2]	(19)	[1],[2]	(8)	[1],[2]
Total revenues	(11)		(126)		(120)		(157)
Inter-segment expenses	40	[1],[2]	8	[1],[2]	47	[1],[2]	18	[1],[2]
Total expenses	70		41		108		83
Income (loss) before income taxes	(81)		(167)		(228)		(240)
Identifiable assets	3,205		5,640		3,205		5,640
Eliminations [Member]
Segment Reporting Information [Line Items]
Inter-segment revenues	(78)	[1]	(67)	[1]	(138)	[1]	(121)	[1]
Total revenues	(78)		(67)		(138)		(119)
Inter-segment expenses	(133)	[1]	(72)	[1]	(220)	[1]	(140)	[1]
Total expenses	(133)		(72)		(220)		(140)
Income (loss) before income taxes	55		5		82		21
Non Variable Interest Entities [Member]
Segment Reporting Information [Line Items]
Revenues	251	[3]	255	[3]	458	[3]	520	[3]
Realized gains and other settlements on insured derivatives	(428)		(191)		(432)		(546)
Unrealized gains (losses) on insured derivatives	1,203		116		1,506		(1,307)
Net gains (losses) on financial instruments at fair value and foreign exchange	(6)		(103)		(25)		(127)
Net investment losses related to other-than-temporary impairments	(3)		(20)		(97)		(33)
Net gains (losses) on extinguishment of debt							26
Other net realized gains (losses)	6				6		5
Loss and loss adjustment expense	62		50		159		14
Operating expenses	93		98		263		189
Interest expense	71		75		145		150
Identifiable assets	22,295		31,668		22,295		31,668
Non Variable Interest Entities [Member] | U.S. Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	145	[3]	143	[3]	270	[3]	274	[3]
Realized gains and other settlements on insured derivatives			1				1
Net gains (losses) on financial instruments at fair value and foreign exchange	11		14		21		17
Loss and loss adjustment expense	(3)		(9)		11		(5)
Operating expenses	23		14		98		26
Identifiable assets	7,120		8,083		7,120		8,083
Non Variable Interest Entities [Member] | Structured Finance And International Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	80	[3]	81	[3]	135	[3]	183	[3]
Realized gains and other settlements on insured derivatives	(428)		(192)		(432)		(547)
Unrealized gains (losses) on insured derivatives	1,203		116		1,506		(1,307)
Net gains (losses) on financial instruments at fair value and foreign exchange	20				66		33
Net investment losses related to other-than-temporary impairments	(1)		(2)		(41)		(4)
Other net realized gains (losses)					1		1
Loss and loss adjustment expense	65		59		148		19
Operating expenses	32		45		91		86
Interest expense	33		33		66		66
Identifiable assets	17,395		23,592		17,395		23,592
Non Variable Interest Entities [Member] | Advisory Services [Member]
Segment Reporting Information [Line Items]
Revenues	5	[3]	7	[3]	11	[3]	13	[3]
Operating expenses	11		18		26		33
Identifiable assets	46		52		46		52
Non Variable Interest Entities [Member] | Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	5	[3]			7	[3]	1	[3]
Net gains (losses) on financial instruments at fair value and foreign exchange	3		16		8		39
Other net realized gains (losses)	6				5
Operating expenses	24		21		45		43
Interest expense	15		14		29		30
Identifiable assets	759		671		759		671
Non Variable Interest Entities [Member] | Wind-Down Operations [Member]
Segment Reporting Information [Line Items]
Revenues	16	[3],[4]	24	[3],[4]	35	[3],[4]	49	[3],[4]
Net gains (losses) on financial instruments at fair value and foreign exchange	(40)		(133)		(120)		(216)
Net investment losses related to other-than-temporary impairments	(2)		(18)		(56)		(29)
Net gains (losses) on extinguishment of debt							24
Other net realized gains (losses)							4
Operating expenses	3				3		1
Interest expense	23		28		50		54
Identifiable assets	3,205		5,640		3,205		5,640
Non Variable Interest Entities [Member] | Eliminations [Member]
Segment Reporting Information [Line Items]
Net gains (losses) on extinguishment of debt							2
Identifiable assets	(6,230)	[5]	(6,370)	[5]	(6,230)	[5]	(6,370)	[5]
Variable Interest Entity [Member]
Segment Reporting Information [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	(34)		22		(61)		(85)
Net gains (losses) on extinguishment of debt	33				33
Other net realized gains (losses)			3				3
Revenues of consolidated VIEs	16		41		6		(48)
Interest expense	15		15		30		30
Expenses of consolidated VIEs	18		22		39		47
Identifiable assets	8,400				8,400				10,900
Variable Interest Entity [Member] | Structured Finance And International Insurance [Member]
Segment Reporting Information [Line Items]
Revenues of consolidated VIEs	(20)		37		(34)		(67)
Expenses of consolidated VIEs	14		17		31		37
Variable Interest Entity [Member] | Wind-Down Operations [Member]
Segment Reporting Information [Line Items]
Revenues of consolidated VIEs	36		4		40		19
Expenses of consolidated VIEs	$ 4		$ 5		$ 8		$ 10

[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] 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.

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

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