Business Segments (Summary Of Company's Operations) (Details) (USD $) In Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010		Dec. 31, 2010
Variable Interest Entity [Line Items]
Revenues	$ 284	[1]	$ 265	[1]	$ 802	[1]	$ 940	[1]
Realized gains and other settlements on insured derivatives	(53)		552		(599)		454
Unrealized gains (losses) on insured derivatives	776		(1,044)		(531)		(1,717)
Net gains (losses) on financial instruments at fair value and foreign exchange	13		12		(114)		(36)
Net investment losses related to other-than-temporary impairments	(11)		0		(44)		(43)
Net gains (losses) on extinguishment of debt			10		26		28
Other net realized gains (losses)	1		(1)		6		18
Revenues of consolidated VIEs	110		15		64		386
Total revenues	1,120		(191)		(390)		30
Loss and loss adjustment expense	190		(20)		204		122
Operating expenses	88		84		277		251
Interest expense	75		81		225		246
Expenses of consolidated VIEs	22		20		69		58
Total expenses	375		165		775		677
Income (loss) before income taxes	745		(356)		(1,165)		(647)
Identifiable assets	29,370		33,272		29,370		33,272		32,279
Non Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Realized gains and other settlements on insured derivatives	(53)		552		(599)		454
Unrealized gains (losses) on insured derivatives	776		(1,044)		(531)		(1,717)
Net gains (losses) on financial instruments at fair value and foreign exchange	13		12		(114)		(36)
Net investment losses related to other-than-temporary impairments	(11)				(44)		(43)
Net gains (losses) on extinguishment of debt			10		26		28
Other net realized gains (losses)	1		(1)		6		18
Loss and loss adjustment expense	190		(20)		204		122
Interest expense	75		81		225		246
U.S. Public Finance Insurance [Member]
Variable Interest Entity [Line Items]
Revenues	181	[1]	143	[1]	455	[1]	459	[1]
Realized gains and other settlements on insured derivatives			0		2		0
Unrealized gains (losses) on insured derivatives			0				0
Net gains (losses) on financial instruments at fair value and foreign exchange	6		45		24		49
Other net realized gains (losses)							0
Inter-segment revenues	21	[2]	18	[2]	56	[2]	66	[2]
Total revenues	208		206		537		574
Loss and loss adjustment expense	10		6		4		42
Operating expenses	10		11		36		31
Inter-segment expenses	31	[2]	22	[2]	84	[2]	74	[2]
Total expenses	51		39		124		147
Income (loss) before income taxes	157		167		413		427
Identifiable assets	8,015		8,616		8,015		8,616
Structured Finance And International Insurance [Member]
Variable Interest Entity [Line Items]
Revenues	72	[1]	89	[1]	253	[1]	370	[1]
Realized gains and other settlements on insured derivatives	(53)		552		(601)		454
Unrealized gains (losses) on insured derivatives	776		(1,044)		(531)		(1,717)
Net gains (losses) on financial instruments at fair value and foreign exchange	(12)		145		21		131
Net investment losses related to other-than-temporary impairments			0		(4)		(4)
Other net realized gains (losses)	1		(1)		2		18
Revenues of consolidated VIEs	105		(19)		39		310
Inter-segment revenues	25	[2]	19	[2]	55	[2]	69	[2]
Total revenues	914		(259)		(766)		(369)
Loss and loss adjustment expense	180		(26)		200		80
Operating expenses	38		31		124		102
Interest expense	33		34		99		102
Expenses of consolidated VIEs	17		15		54		46
Inter-segment expenses	33	[2]	28	[2]	91	[2]	103	[2]
Total expenses	301		82		568		433
Income (loss) before income taxes	613		(341)		(1,334)		(802)
Identifiable assets	21,251		24,321		21,251		24,321
Advisory Services [Member]
Variable Interest Entity [Line Items]
Revenues	9	[1]	7	[1]	22	[1]	21	[1]
Net gains (losses) on financial instruments at fair value and foreign exchange			1				2
Other net realized gains (losses)							0
Inter-segment revenues	5	[2]	10	[2]	24	[2]	29	[2]
Total revenues	14		18		46		52
Operating expenses	14		17		48		45
Inter-segment expenses	1	[2]	2	[2]	4	[2]	5	[2]
Total expenses	15		19		52		50
Income (loss) before income taxes	(1)		(1)		(6)		2
Identifiable assets	53		51		53		51
Corporate Operations [Member]
Variable Interest Entity [Line Items]
Revenues	1	[1]	1	[1]	2	[1]	3	[1]
Net gains (losses) on financial instruments at fair value and foreign exchange	8		(62)		47		(80)
Net investment losses related to other-than-temporary impairments	(10)				(10)
Net gains (losses) on extinguishment of debt			0				0
Other net realized gains (losses)							0
Inter-segment revenues	22	[2]	24	[2]	66	[2]	74	[2]
Total revenues	21		(37)		105		(3)
Operating expenses	24		23		67		69
Interest expense	14		16		44		49
Inter-segment expenses	4	[2]	4	[2]	11	[2]	10	[2]
Total expenses	42		43		122		128
Income (loss) before income taxes	(21)		(80)		(17)		(131)
Identifiable assets	652		1,308		652		1,308
Wind-Down Operations [Member]
Variable Interest Entity [Line Items]
Revenues	21	[1],[3]	25	[1],[3]	70	[1],[3]	87	[1],[3]
Net gains (losses) on financial instruments at fair value and foreign exchange	11		(117)		(206)		(138)
Net investment losses related to other-than-temporary impairments	(1)		0		(30)		(39)
Net gains (losses) on extinguishment of debt			10		24		28
Other net realized gains (losses)					4		0
Revenues of consolidated VIEs	5		34		25		76
Inter-segment revenues	(4)	[2],[4]	(5)	[2],[4]	(12)	[2],[4]	(15)	[2],[4]
Total revenues	32		(53)		(125)		(1)
Operating expenses	2		2		2		4
Interest expense	28		31		82		95
Expenses of consolidated VIEs	5		5		15		12
Inter-segment expenses	6	[2],[4]	13	[2],[4]	24	[2],[4]	47	[2],[4]
Total expenses	41		51		123		158
Income (loss) before income taxes	(9)		(104)		(248)		(159)
Identifiable assets	5,556		7,008		5,556		7,008
Eliminations [Member]
Variable Interest Entity [Line Items]
Net gains (losses) on extinguishment of debt					2
Inter-segment revenues	(69)	[2]	(66)	[2]	(189)	[2]	(223)	[2]
Total revenues	(69)		(66)		(187)		(223)
Inter-segment expenses	(75)	[2]	(69)	[2]	(214)	[2]	(239)	[2]
Total expenses	(75)		(69)		(214)		(239)
Income (loss) before income taxes	6		3		27		16
Identifiable assets	$ (6,157)	[5]	$ (8,032)	[5]	$ (6,157)	[5]	$ (8,032)	[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]

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

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