Business Segments (Summary Of Company's Operations) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Variable Interest Entity [Line Items]
Unrealized gains (losses) on insured derivatives	$ (441)		$ (607)		$ 1,650
Net gains (losses) on extinguishment of debt	26		60		269
Revenues of consolidated VIEs	392		364		(19)
Total revenues	(1,557)		894		2,954
Expenses of consolidated VIEs	91		83		102
Total expenses	682		989		1,737
Income (loss) before income taxes	(2,239)		(95)		1,217
Identifiable assets	26,873		32,279		25,701
U.S. Public Finance Insurance [Member]
Variable Interest Entity [Line Items]
Inter-segment revenues	79	[1]	93	[1]	146	[1]
Total revenues	745		750		808
Inter-segment expenses	114	[1]	104	[1]	125	[1]
Total expenses	170		220		257
Income (loss) before income taxes	575		530		551
Identifiable assets	7,848		8,436		8,184
Structured Finance And International Insurance [Member]
Variable Interest Entity [Line Items]
Revenues of consolidated VIEs	361		246		(58)
Inter-segment revenues	91	[1]	113	[1]	177	[1]
Total revenues	(2,046)		211		2,194
Expenses of consolidated VIEs	70		64		88
Inter-segment expenses	124	[1]	135	[1]	116	[1]
Total expenses	409		642		1,370
Income (loss) before income taxes	(2,455)		(431)		824
Identifiable assets	19,985		23,980		16,447
Advisory Services [Member]
Variable Interest Entity [Line Items]
Inter-segment revenues	41	[1]	38	[1]	22	[1]
Total revenues	67		70		54
Inter-segment expenses	6	[1]	7	[1]	1	[1]
Total expenses	64		71		49
Income (loss) before income taxes	3		(1)		5
Identifiable assets	53		54		125
Corporate Operations [Member]
Variable Interest Entity [Line Items]
Inter-segment revenues	152	[1]	94	[1]	19	[1]
Total revenues	196		70		24
Inter-segment expenses	22	[1]	14	[1]
Total expenses	172		168		93
Income (loss) before income taxes	24		(98)		(69)
Identifiable assets	829		653		1,276
Wind-Down Operations [Member]
Variable Interest Entity [Line Items]
Revenues	90	[2]	113	[2]	193	[2]
Net gains (losses) on financial instruments at fair value and foreign exchange	(276)		(76)		146
Net investment losses related to other-than-temporary impairments	(31)		(59)		(352)
Net gains (losses) on extinguishment of debt	24		35		203
Other net realized gains (losses)	4		0		4
Revenues of consolidated VIEs	31		96		39
Inter-segment revenues	(23)	[1],[3]	(18)	[1],[3]	(3)	[1],[3]
Total revenues	(181)		91		230
Operating expenses	3		4		27
Interest	109		125		169
Expenses of consolidated VIEs	21		19		14
Inter-segment expenses	95	[1],[3]	60	[1],[3]	116	[1],[3]
Total expenses	228		208		326
Income (loss) before income taxes	(409)		(117)		(96)
Identifiable assets	5,203		6,432		8,092
Eliminations [Member]
Variable Interest Entity [Line Items]
Revenues of consolidated VIEs			22
Inter-segment revenues	(340)	[1]	(320)	[1]	(361)	[1]
Total revenues	(338)		(298)		(356)
Inter-segment expenses	(361)	[1]	(320)	[1]	(358)	[1]
Total expenses	(361)		(320)		(358)
Income (loss) before income taxes	23		22		2
Identifiable assets	(7,045)	[4]	(7,276)	[4]	(8,423)	[4]
Non Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Revenues	1,038	[5]	1,211	[5]	1,460	[5]
Realized gains (losses) and other settlements on insured derivatives	(2,371)		(162)		(166)
Unrealized gains (losses) on insured derivatives	(441)		(607)		1,650
Net gains (losses) on financial instruments at fair value and foreign exchange	(99)		88		225
Net investment losses related to other-than-temporary impairments	(101)		(64)		(361)
Net gains (losses) on extinguishment of debt	26		35		225
Other net realized gains (losses)	(1)		29		(60)
Loss and loss adjustment expense	(80)		232		864
Operating expenses	371		349		397
Interest	300		325		374
Non Variable Interest Entities [Member] | U.S. Public Finance Insurance [Member]
Variable Interest Entity [Line Items]
Revenues	599	[5]	601	[5]	638	[5]
Realized gains (losses) and other settlements on insured derivatives	2		1		1
Net gains (losses) on financial instruments at fair value and foreign exchange	96		55		23
Other net realized gains (losses)	(31)
Loss and loss adjustment expense	4		73		94
Operating expenses	52		43		38
Non Variable Interest Entities [Member] | Structured Finance And International Insurance [Member]
Variable Interest Entity [Line Items]
Revenues	319	[5]	463	[5]	593	[5]
Realized gains (losses) and other settlements on insured derivatives	(2,373)		(163)		(167)
Unrealized gains (losses) on insured derivatives	(441)		(607)		1,650
Net gains (losses) on financial instruments at fair value and foreign exchange	58		135		59
Net investment losses related to other-than-temporary impairments	(62)		(5)		(9)
Net gains (losses) on extinguishment of debt					13
Other net realized gains (losses)	1		29		(64)
Loss and loss adjustment expense	(84)		159		770
Operating expenses	166		149		260
Interest	133		135		136
Non Variable Interest Entities [Member] | Advisory Services [Member]
Variable Interest Entity [Line Items]
Revenues	26	[5]	30	[5]	32	[5]
Net gains (losses) on financial instruments at fair value and foreign exchange			2
Operating expenses	58		64		48
Non Variable Interest Entities [Member] | Corporate Operations [Member]
Variable Interest Entity [Line Items]
Revenues	4	[5]	4	[5]	4	[5]
Net gains (losses) on financial instruments at fair value and foreign exchange	23		(28)		(3)
Net investment losses related to other-than-temporary impairments	(8)
Net gains (losses) on extinguishment of debt					4
Other net realized gains (losses)	25
Operating expenses	92		89		24
Interest	58		65		69
Non Variable Interest Entities [Member] | Wind-Down Operations [Member]
Variable Interest Entity [Line Items]
Revenues	90	[5]	113	[5]	193	[5]
Net gains (losses) on financial instruments at fair value and foreign exchange	(276)		(76)		146
Net investment losses related to other-than-temporary impairments	(31)		(59)		(352)
Net gains (losses) on extinguishment of debt	24		35		203
Other net realized gains (losses)	4				4
Operating expenses	3		4		27
Interest	109		125		169
Non Variable Interest Entities [Member] | Eliminations [Member]
Variable Interest Entity [Line Items]
Net gains (losses) on extinguishment of debt	2				5
Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	59		342		(4)
Net investment losses related to other-than-temporary impairments					(106)
Net gains (losses) on extinguishment of debt			25		44
Other net realized gains (losses)	263		(76)		(41)
Interest	62		59		101
Identifiable assets	$ 10,900		$ 14,100

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

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

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

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

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