Consolidated Statements Of Operations (USD $) In Millions, except Share data	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010
Change in fair value of insured derivatives:
Realized gains (losses) 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)
Investment losses related to other-than-temporary impairments:
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
Total revenues	1,120		(191)		(390)		30
Expenses:
Losses and loss adjustment	190		(20)		204		122
Interest	75		81		225		246
Total expenses	375		165		775		677
Income (loss) before income taxes	745		(356)		(1,165)		(647)
Provision (benefit) for income taxes	301		(143)		(472)		(249)
Net income (loss)	444		(213)		(693)		(398)
Net income (loss) per common share:
Basic	$ 2.27		$ (1.06)		$ (3.50)		$ (1.96)
Diluted	$ 2.26		$ (1.06)		$ (3.50)		$ (1.96)
Weighted average number of common shares outstanding:
Basic	195,612,615	[1]	200,529,483	[1]	198,262,715	[1]	203,239,935	[1]
Diluted	196,347,502		200,529,483		198,262,715		203,239,935
Non Variable Interest Entities [Member]
Premiums earned:
Scheduled premiums earned	111		123		354		386
Refunding premiums earned	65		14		108		64
Premiums earned (net of ceded premiums of $3, $4, $9 and $24)	176		137		462		450
Net investment income	92		113		299		342
Fees and reimbursements	16		15		41		148
Change in fair value of insured derivatives:
Realized gains (losses) and other settlements on insured derivatives	(53)		552		(599)		454
Unrealized gains (losses) on insured derivatives	776		(1,044)		(531)		(1,717)
Net change in fair value of insured derivatives	723		(492)		(1,130)		(1,263)
Net gains (losses) on financial instruments at fair value and foreign exchange	13		12		(114)		(36)
Investment losses related to other-than-temporary impairments:
Investment losses related to other-than-temporary impairments	(12)				(25)		(187)
Other-than-temporary impairments recognized in accumulated other comprehensive loss	1				(19)		144
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
Expenses:
Losses and loss adjustment	190		(20)		204		122
Amortization of deferred acquisition costs	12		6		51		42
Operating	76		78		226		209
Interest	75		81		225		246
Variable Interest Entity, Primary Beneficiary [Member]
Premiums earned:
Net investment income	17		20		53		48
Change in fair value of insured derivatives:
Net gains (losses) on financial instruments at fair value and foreign exchange	88		(19)		3		394
Investment losses related to other-than-temporary impairments:
Net gains (losses) on extinguishment of debt			14				18
Other net realized gains (losses)	5				8		(74)
Expenses:
Operating	7		4		24		14
Interest	$ 15		$ 16		$ 45		$ 44

[1] Includes 5,038,788 and 5,288,205 of unvested restricted stock and units that receive nonforfeitable dividends or dividend equivalents for the three months ended September 30, 2011 and 2010, respectively. Includes 5,085,256 and 5,364,012 of unvested restricted stock and units that receive nonforfeitable dividends or dividend equivalents for the nine months ended September 30, 2011 and 2010, respectively.