Business Segments (Summary Of Company's Segment Results) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012		Mar. 31, 2011		Dec. 31, 2011
Variable Interest Entity [Line Items]
Unrealized gains (losses) on insured derivatives	$ 303		$ (1,422)
Total revenues	383		(1,607)
Loss and loss adjustment expense	97
Total expenses	362		156
Income (loss) before income taxes	21		(1,763)
Identifiable assets	26,126		32,243		26,873
U.S. Public Finance Insurance [Member]
Variable Interest Entity [Line Items]
Inter-segment revenues	36	[1]	18	[1]
Total revenues	171		152
Inter-segment expenses	27	[1]	26	[1]
Total expenses	116		41
Income (loss) before income taxes	55		111
Identifiable assets	7,534		8,232
Structured Finance And International Insurance [Member]
Variable Interest Entity [Line Items]
Inter-segment revenues	(7)	[1]	11	[1]
Total revenues	340		(1,736)
Inter-segment expenses	46	[1]	29	[1]
Total expenses	238		85
Income (loss) before income taxes	102		(1,821)
Identifiable assets	19,632		24,179
Advisory Services [Member]
Variable Interest Entity [Line Items]
Inter-segment revenues	7	[1]	9	[1]
Total revenues	13		15
Inter-segment expenses	2	[1]	1	[1]
Total expenses	17		16
Income (loss) before income taxes	(4)		(1)
Identifiable assets	46		54
Corporate [Member]
Variable Interest Entity [Line Items]
Inter-segment revenues	23	[1]	22	[1]
Total revenues	29		46
Inter-segment expenses	4	[1]	4	[1]
Total expenses	39		41
Income (loss) before income taxes	(10)		5
Identifiable assets	670		624
Wind-Down Operations [Member]
Variable Interest Entity [Line Items]
Inter-segment revenues	3	[1],[2]	(5)	[1],[2]
Total revenues	(108)		(31)
Inter-segment expenses	8	[1],[2]	9	[1],[2]
Total expenses	39		42
Income (loss) before income taxes	(147)		(73)
Identifiable assets	4,732		6,161
Eliminations [Member]
Variable Interest Entity [Line Items]
Inter-segment revenues	(62)	[1]	(55)	[1]
Total revenues	(62)		(53)
Inter-segment expenses	(87)	[1]	(69)	[1]
Total expenses	(87)		(69)
Income (loss) before income taxes	25		16
Identifiable assets	(6,488)	[3]	(7,007)	[3]
Non Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Revenues	206	[4]	265	[4]
Realized gains and other settlements on insured derivatives	(4)		(354)
Unrealized gains (losses) on insured derivatives	303		(1,422)
Net gains (losses) on financial instruments at fair value and foreign exchange	(19)		(24)
Net investment losses related to other-than-temporary impairments	(94)		(13)
Net gains (losses) on extinguishment of debt			26
Other net realized gains (losses)	1		5
Loss and loss adjustment expense	97		(36)
Operating expenses	171		92
Interest expense	73		75
Non Variable Interest Entities [Member] | U.S. Public Finance Insurance [Member]
Variable Interest Entity [Line Items]
Revenues	125	[4]	131	[4]
Net gains (losses) on financial instruments at fair value and foreign exchange	10		3
Loss and loss adjustment expense	14		3
Operating expenses	75		12
Non Variable Interest Entities [Member] | Structured Finance And International Insurance [Member]
Variable Interest Entity [Line Items]
Revenues	55	[4]	102	[4]
Realized gains and other settlements on insured derivatives	(4)		(354)
Unrealized gains (losses) on insured derivatives	303		(1,422)
Net gains (losses) on financial instruments at fair value and foreign exchange	46		33
Net investment losses related to other-than-temporary impairments	(40)		(2)
Other net realized gains (losses)	1		1
Loss and loss adjustment expense	83		(39)
Operating expenses	59		42
Interest expense	33		33
Non Variable Interest Entities [Member] | Advisory Services [Member]
Variable Interest Entity [Line Items]
Revenues	6	[4]	6	[4]
Operating expenses	15		15
Non Variable Interest Entities [Member] | Corporate [Member]
Variable Interest Entity [Line Items]
Revenues	1	[4]	1	[4]
Net gains (losses) on financial instruments at fair value and foreign exchange	5		23
Operating expenses	21		22
Interest expense	14		15
Non Variable Interest Entities [Member] | Wind-Down Operations [Member]
Variable Interest Entity [Line Items]
Revenues	19	[4],[5]	25	[4],[5]
Net gains (losses) on financial instruments at fair value and foreign exchange	(80)		(83)
Net investment losses related to other-than-temporary impairments	(54)		(11)
Net gains (losses) on extinguishment of debt			24
Other net realized gains (losses)			4
Operating expenses	1		1
Interest expense	26		27
Non Variable Interest Entities [Member] | Eliminations [Member]
Variable Interest Entity [Line Items]
Net gains (losses) on extinguishment of debt			2
Variable Interest Entity [Member]
Variable Interest Entity [Line Items]
Net gains (losses) on financial instruments at fair value and foreign exchange	(27)		(107)
Revenues of consolidated VIEs	(10)		(90)
Interest expense	15		15
Expenses of consolidated VIEs	21		25
Identifiable assets	10,500				10,900
Variable Interest Entity [Member] | Structured Finance And International Insurance [Member]
Variable Interest Entity [Line Items]
Revenues of consolidated VIEs	(14)		(105)
Expenses of consolidated VIEs	17		20
Variable Interest Entity [Member] | Wind-Down Operations [Member]
Variable Interest Entity [Line Items]
Revenues of consolidated VIEs	4		15
Expenses of consolidated VIEs	$ 4		$ 5

[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.