Consolidated Statements Of Operations (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Change in fair value of insured derivatives:
Unrealized gains (losses) on insured derivatives					$ 1,277		$ 1,506
Net change in fair value of insured derivatives	(182)		775		(243)		1,074
Net gains (losses) on financial instruments at fair value and foreign exchange	(6)		(6)		57		(25)
Investment losses related to other-than-temporary impairments:
Net investment losses related to other-than-temporary impairments	0		(3)		0		(97)
Net gains (losses) on extinguishment of debt	39		0		43		0
Other net realized gains (losses)	0		6		0		6
Total revenues	112		1,039		331		1,422
Expenses:
Losses and loss adjustment	188		62		(6)		159
Interest	60		71		120		145
Total expenses	376		244		380		606
Income (loss) before income taxes	(264)		795		(49)		816
Provision (benefit) for income taxes	(86)		214		(35)		225
Net income (loss)	(178)		581		(14)		591
Net income (loss) per common share:
Basic	$ (0.92)		$ 2.99		$ (0.07)		$ 3.05
Diluted	$ (0.92)		$ 2.98		$ (0.07)		$ 3.03
Weighted average number of common shares outstanding:
Basic	193,104,610	[1]	193,926,953	[1]	193,810,351	[1]	193,700,328	[1]
Diluted	193,104,610		194,941,233		193,810,351		194,763,617
Non Variable Interest Entity [Member]
Premiums earned:
Scheduled premiums earned	77		110		156		206
Refunding premiums earned	47		61		88		103
Premiums earned (net of ceded premiumsof $2, $6, $5 and $9)	124		171		244		309
Net investment income	38		60		76		122
Fees and reimbursements	6		20		12		27
Change in fair value of insured derivatives:
Realized gains (losses) and other settlements on insured derivatives	(1,532)		(428)		(1,520)		(432)
Unrealized gains (losses) on insured derivatives	1,350		1,203		1,277		1,506
Net change in fair value of insured derivatives	(182)		775		(243)		1,074
Net gains (losses) on financial instruments at fair value and foreign exchange	(6)		(6)		57		(25)
Investment losses related to other-than-temporary impairments:
Investment losses related to other-than-temporary impairments	0		(2)		0		(55)
Other-than-temporary impairments recognized in accumulated other comprehensive income (loss)	0		(1)		0		(42)
Net investment losses related to other-than-temporary impairments	0		(3)		0		(97)
Net gains (losses) on extinguishment of debt	39		0		43		0
Other net realized gains (losses)	0		6		0		6
Expenses:
Losses and loss adjustment	188		62		(6)		159
Amortization of deferred acquisition costs	11		15		27		28
Operating	103		78		209		235
Interest	60		71		120		145
Variable Interest Entity Primary Beneficiary [Member]
Premiums earned:
Net investment income	14		17		30		34
Change in fair value of insured derivatives:
Net gains (losses) on financial instruments at fair value and foreign exchange	78		(34)		111		(61)
Investment losses related to other-than-temporary impairments:
Net gains (losses) on extinguishment of debt	0		33		0		33
Other net realized gains (losses)	1		0		1		0
Expenses:
Operating	2		3		6		9
Interest	$ 12		$ 15		$ 24		$ 30

[1] Includes 4,490,348 and 5,597,797 of unvested restricted stock and units that receive nonforfeitable dividends or dividend equivalents for the three months ended June 30, 2013 and 2012,respectively. Includes 5,303,456 and 5,400,564 of unvested restricted stock and units that receive nonforfeitable dividends or dividend equivalents for the six months endedJune 30, 2013 and 2012, respectively.