Business Segments (Summary Of Company's Segment Results) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014		Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 139	[1]	$ 142	[2]
Net change in fair value of insured derivatives	28		469
Net gains (losses) on financial instruments at fair value and foreign exchange	30		(55)
Net gains (losses) on extinguishment of debt			1
Other net realized gains (losses)	20		1
Revenues of consolidated VIEs	2		19
Inter-segment revenues	0	[3]	0	[4]
Total revenues	219		577
Losses and loss adjustment	(6)		50
Operating	48		56
Interest	50		54
Expenses of consolidated VIEs	14		13
Inter-segment expenses	0	[3]	0	[4]
Total expenses	106		173
Income (loss) before income taxes	113		404
Provision (benefit) for income taxes	44		148
Net income (loss)	69		256
Identifiable assets	15,915		16,087		16,284
U S Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Losses and loss adjustment	(6)		(14)
Operating Segments [Member] | U S Public Finance Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	105	[1]	89	[2]
Net change in fair value of insured derivatives			1
Net gains (losses) on financial instruments at fair value and foreign exchange	3		4
Other net realized gains (losses)	(4)
Inter-segment revenues	10	[3]	11	[4]
Total revenues	114		105
Losses and loss adjustment	(6)		(14)
Operating	10		9
Inter-segment expenses	24	[3]	18	[4]
Total expenses	28		13
Income (loss) before income taxes	86		92
Provision (benefit) for income taxes	29		31
Net income (loss)	57		61
Identifiable assets	5,859		6,124
Operating Segments [Member] | International And Structured Finance Insurance [Member]
Segment Reporting Information [Line Items]
Revenues	29	[1]	32	[2]
Net change in fair value of insured derivatives	28		468
Net gains (losses) on financial instruments at fair value and foreign exchange	(5)		(3)
Revenues of consolidated VIEs	2		20
Inter-segment revenues	18	[3]	12	[4]
Total revenues	72		529
Losses and loss adjustment			64
Operating	19		17
Interest	25		28
Expenses of consolidated VIEs	14		13
Inter-segment expenses	18	[3]	17	[4]
Total expenses	76		139
Income (loss) before income taxes	(4)		390
Provision (benefit) for income taxes	(2)		136
Net income (loss)	(2)		254
Identifiable assets	10,578		10,867
Operating Segments [Member] | Corporate Operations [Member]
Segment Reporting Information [Line Items]
Revenues	5	[1]	18	[2]
Net gains (losses) on financial instruments at fair value and foreign exchange	32		(52)
Net gains (losses) on extinguishment of debt	0		1
Other net realized gains (losses)	24		1
Revenues of consolidated VIEs			(5)
Inter-segment revenues	16	[3]	7	[4]
Total revenues	77		(30)
Operating	19		19
Interest	25		26
Inter-segment expenses	1	[3]	4	[4]
Total expenses	45		49
Income (loss) before income taxes	32		(79)
Provision (benefit) for income taxes	17		(21)
Net income (loss)	15		(58)
Identifiable assets	2,737		2,640
Operating Segments [Member] | Advisory Services [Member]
Segment Reporting Information [Line Items]
Revenues			3	[2]
Net gains (losses) on financial instruments at fair value and foreign exchange			(4)
Inter-segment revenues			6	[4]
Total revenues			5
Operating			11
Inter-segment expenses			1	[4]
Total expenses			12
Income (loss) before income taxes			(7)
Provision (benefit) for income taxes			(1)
Net income (loss)			(6)
Identifiable assets			34
Operating Segments [Member] | Conduit [Member]
Segment Reporting Information [Line Items]
Revenues of consolidated VIEs			4
Inter-segment revenues			(1)	[4]
Total revenues			3
Income (loss) before income taxes			3
Provision (benefit) for income taxes			1
Net income (loss)			2
Identifiable assets			76
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Net gains (losses) on extinguishment of debt			0
Inter-segment revenues	(44)	[3]	(35)	[4]
Total revenues	(44)		(35)
Inter-segment expenses	(43)	[3]	(40)	[4]
Total expenses	(43)		(40)
Income (loss) before income taxes	(1)		5
Provision (benefit) for income taxes	0		2
Net income (loss)	(1)		3
Identifiable assets	$ (3,259)	[5]	$ (3,654)	[5]

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

[2] 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.

[3] Represents intercompany premium income and expense and intercompany interest income and expense pertaining to intercompany receivables and payables.

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

[5] Consists of intercompany reinsurance balances, repurchase agreements and deferred income taxes.