Consolidated Statements Of Operations (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2012		Jun. 30, 2011		Jun. 30, 2012		Jun. 30, 2011
Change in fair value of insured derivatives:
Unrealized gains (losses) on insured derivatives					$ (1,506)		$ 1,307
Investment losses related to other-than-temporary impairments:
Total revenues	1,039		98		1,422		(1,510)
Expenses:
Losses and loss adjustment					159
Total expenses	244		245		606		400
Income (loss) before income taxes	795		(147)		816		(1,910)
Provision (benefit) for income taxes	214		(284)		225		(772)
Net income (loss)	581		137		591		(1,138)
Net income (loss) per common share:
Basic	$ 2.99		$ 0.69		$ 3.05		$ (5.70)
Diluted	$ 2.98		$ 0.68		$ 3.03		$ (5.70)
Weighted average number of common shares outstanding:
Basic	193,926,953	[1]	199,295,797	[1]	193,700,328	[1]	199,602,865	[1]
Diluted	194,941,233		200,064,679		194,763,617		199,602,865
Non Variable Interest Entities [Member]
Premiums earned:
Scheduled premiums earned	110		116		206		243
Refunding premiums earned	61		33		103		43
Premiums earned (net of ceded premiums of $6, $3, $9 and $6)	171		149		309		286
Net investment income	60		95		122		209
Fees and reimbursements	20		11		27		25
Change in fair value of insured derivatives:
Realized gains (losses) and other settlements on insured derivatives	(428)		(191)		(432)		(546)
Unrealized gains (losses) on insured derivatives	1,203		116		1,506		(1,307)
Net change in fair value of insured derivatives	775		(75)		1,074		(1,853)
Net gains (losses) on financial instruments at fair value and foreign exchange	(6)		(103)		(25)		(127)
Investment losses related to other-than-temporary impairments:
Investment losses related to other-than-temporary impairments	(2)		(6)		(55)		(13)
Net investment income	60		95		122		209
Other-than-temporary impairments recognized in accumulated other comprehensive income (loss)	(1)		(14)		(42)		(20)
Net gains (losses) on financial instruments at fair value and foreign exchange	(6)		(103)		(25)		(127)
Net investment losses related to other-than-temporary impairments	(3)		(20)		(97)		(33)
Net gains (losses) on extinguishment of debt							26
Other net realized gains (losses)	6				6		5
Expenses:
Losses and loss adjustment	62		50		159		14
Amortization of deferred acquisition costs	15		23		28		39
Operating	78		75		235		150
Interest	71		75		145		150
Variable Interest Entity [Member]
Premiums earned:
Net investment income	17		16		34		34
Change in fair value of insured derivatives:
Net gains (losses) on financial instruments at fair value and foreign exchange	(34)		22		(61)		(85)
Investment losses related to other-than-temporary impairments:
Net investment income	17		16		34		34
Net gains (losses) on financial instruments at fair value and foreign exchange	(34)		22		(61)		(85)
Net gains (losses) on extinguishment of debt	33				33
Other net realized gains (losses)			3				3
Expenses:
Operating	3		7		9		17
Interest	$ 15		$ 15		$ 30		$ 30

[1] Includes 5,597,797 and 5,035,256 of unvested restricted stock and units that receive nonforfeitable dividends or dividend equivalents for the three months ended June 30, 2012 and 2011, respectively. Includes 5,400,564 and 5,102,013 of unvested restricted stock and units that receive nonforfeitable dividends or dividend equivalents for the six months ended June 30, 2012 and 2011, respectively.