Business Segments (Summary Of Company's Segment Results) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012		Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 168	[1]	$ 251	[1]	$ 332	[1]	$ 458	[1]
Net change in fair value of insured derivatives	(182)		775		(243)		1,074
Net gains (losses) on financial instruments at fair value and foreign exchange	(6)		(6)		57		(25)
Net investment losses related to other-than-temporary impairments	0		(3)		0		(97)
Net gains (losses) on extinguishment of debt	39		0		43		0
Other net realized gains (losses)	0		6		0		6
Revenues of consolidated VIEs	93		16		142		6
Inter-segment revenues	0	[2]	0	[2]	0	[2]	0	[2]
Total revenues	112		1,039		331		1,422
Losses and loss adjustment	188		62		(6)		159
Operating	114		93		236		263
Interest	60		71		120		145
Expenses of consolidated VIEs	14		18		30		39
Inter-segment expenses	0	[2]	0	[2]	0	[2]	0	[2]
Total expenses	376		244		380		606
Income (loss) before income taxes	(264)		795		(49)		816
Identifiable assets	18,122		22,295		18,122		22,295		21,724
Non Variable Interest Entity [Member]
Segment Reporting Information [Line Items]
Net change in fair value of insured derivatives	(182)		775		(243)		1,074
Net gains (losses) on financial instruments at fair value and foreign exchange	(6)		(6)		57		(25)
Net investment losses related to other-than-temporary impairments	0		(3)		0		(97)
Net gains (losses) on extinguishment of debt	39		0		43		0
Other net realized gains (losses)	0		6		0		6
Losses and loss adjustment	188		62		(6)		159
Interest	60		71		120		145
Variable Interest Entity Primary Beneficiary [Member]
Segment Reporting Information [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	78		(34)		111		(61)
Net gains (losses) on extinguishment of debt	0		33		0		33
Other net realized gains (losses)	1		0		1		0
Interest	12		15		24		30
U S Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	113	[1]	145	[1]	221	[1]	270	[1]
Net change in fair value of insured derivatives	0		0		0		0
Net gains (losses) on financial instruments at fair value and foreign exchange	(2)		11		30		21
Net investment losses related to other-than-temporary impairments	0		0		0		0
Net gains (losses) on extinguishment of debt	22		0		22		0
Other net realized gains (losses)	0		0		0		0
Revenues of consolidated VIEs	0		0		0		0
Inter-segment revenues	3	[2]	43	[2]	49	[2]	79	[2]
Total revenues	136		199		322		370
Losses and loss adjustment	66		(3)		70		11
Operating	30		23		44		98
Interest	0		0		0		0
Expenses of consolidated VIEs	0		0		0		0
Inter-segment expenses	26	[2]	31	[2]	52	[2]	59	[2]
Total expenses	122		51		166		168
Income (loss) before income taxes	14		148		156		202
Identifiable assets	6,651		7,120		6,651		7,120
Structured Finance And International Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	39	[1]	80	[1]	81	[1]	135	[1]
Net change in fair value of insured derivatives	(182)		775		(243)		1,074
Net gains (losses) on financial instruments at fair value and foreign exchange	12		20		34		66
Net investment losses related to other-than-temporary impairments	0		(1)		0		(41)
Net gains (losses) on extinguishment of debt	17		0		17		0
Other net realized gains (losses)	0				0		1
Revenues of consolidated VIEs	97		(20)		144		(34)
Inter-segment revenues	(5)	[2]	(11)	[2]	15	[2]	(19)	[2]
Total revenues	(22)		843		48		1,182
Losses and loss adjustment	122		65		(76)		148
Operating	35		32		69		91
Interest	29		33		57		66
Expenses of consolidated VIEs	12		14		26		31
Inter-segment expenses	36	[2]	54	[2]	92	[2]	100	[2]
Total expenses	234		198		168		436
Income (loss) before income taxes	(256)		645		(120)		746
Identifiable assets	12,669		17,395		12,669		17,395
Advisory Services [Member]
Segment Reporting Information [Line Items]
Revenues	6	[1]	5	[1]	10	[1]	11	[1]
Net change in fair value of insured derivatives	0		0		0		0
Net gains (losses) on financial instruments at fair value and foreign exchange	0		0		0		0
Net investment losses related to other-than-temporary impairments	0		0		0		0
Net gains (losses) on extinguishment of debt	0		0		0		0
Other net realized gains (losses)	0		0		0		0
Revenues of consolidated VIEs	0		0		0		0
Inter-segment revenues	5	[2]	11	[2]	12	[2]	18	[2]
Total revenues	11		16		22		29
Losses and loss adjustment	0		0		0		0
Operating	16		11		26		26
Interest	0		0		0		0
Expenses of consolidated VIEs	0		0		0		0
Inter-segment expenses	1	[2]	5	[2]	3	[2]	7	[2]
Total expenses	17		16		29		33
Income (loss) before income taxes	(6)		0		(7)		(4)
Identifiable assets	46		46		46		46
Corporate Operations [Member]
Segment Reporting Information [Line Items]
Revenues	4	[1]	5	[1]	5	[1]	7	[1]
Net change in fair value of insured derivatives	0		0		0		0
Net gains (losses) on financial instruments at fair value and foreign exchange	(4)		3		2		8
Net investment losses related to other-than-temporary impairments	0		0		0		0
Net gains (losses) on extinguishment of debt	0		0		0		0
Other net realized gains (losses)	0		6		0		5
Revenues of consolidated VIEs	(9)		0		(9)		0
Inter-segment revenues	(5)	[2]	56	[2]	21	[2]	79	[2]
Total revenues	(14)		70		19		99
Losses and loss adjustment	0		0		0		0
Operating	32		24		96		45
Interest	11		15		23		29
Expenses of consolidated VIEs	0		0		0		0
Inter-segment expenses	2	[2]	3	[2]	5	[2]	7	[2]
Total expenses	45		42		124		81
Income (loss) before income taxes	(59)		28		(105)		18
Identifiable assets	931		759		931		759
Wind Down Operations [Member]
Segment Reporting Information [Line Items]
Revenues	6	[1],[3]	16	[1]	15	[1],[3]	35	[1],[3]
Net change in fair value of insured derivatives	0		0		0		0
Net gains (losses) on financial instruments at fair value and foreign exchange	(12)		(40)		(9)		(120)
Net investment losses related to other-than-temporary impairments	0		(2)		0		(56)
Net gains (losses) on extinguishment of debt	0		0		4		0
Other net realized gains (losses)	0		0		0		0
Revenues of consolidated VIEs	5		36		7		40
Inter-segment revenues	0	[2],[4]	(21)	[2],[4]	(2)	[2],[4]	(19)	[2],[4]
Total revenues	(1)		(11)		15		(120)
Losses and loss adjustment	0		0		0		0
Operating	1		3		1		3
Interest	20		23		40		50
Expenses of consolidated VIEs	2		4		4		8
Inter-segment expenses	2	[2],[4]	40	[2],[4]	15	[2],[4]	47	[2],[4]
Total expenses	25		70		60		108
Income (loss) before income taxes	(26)		(81)		(45)		(228)
Identifiable assets	2,009		3,205		2,009		3,205
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Revenues	0	[1]	0	[1]	0	[1]	0	[1]
Net change in fair value of insured derivatives	0		0		0		0
Net gains (losses) on financial instruments at fair value and foreign exchange	0		0		0		0
Net investment losses related to other-than-temporary impairments	0		0		0		0
Net gains (losses) on extinguishment of debt	0		0		0		0
Other net realized gains (losses)	0				0		0
Revenues of consolidated VIEs	0		0		0		0
Inter-segment revenues	2	[2]	(78)	[2]	(95)	[2]	(138)	[2]
Total revenues	2		(78)		(95)		(138)
Losses and loss adjustment	0		0		0		0
Operating	0		0		0		0
Interest	0		0		0		0
Expenses of consolidated VIEs	0		0		0		0
Inter-segment expenses	(67)	[2]	(133)	[2]	(167)	[2]	(220)	[2]
Total expenses	(67)		(133)		(167)		(220)
Income (loss) before income taxes	69		55		72		82
Identifiable assets	$ (4,184)	[5]	$ (6,230)	[5]	$ (4,184)	[5]	$ (6,230)	[5]

[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, and intercompany interest income and expense pertaining to intercompany receivables and payables.

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

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

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