Consolidated Statements Of Operations (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Change in fair value of insured derivatives:
Realized gains (losses) and other settlements on insured derivatives					$ 607
Unrealized gains (losses) on insured derivatives	1,870		(441)		(607)
Investment losses related to other-than-temporary impairments:
Net gains (losses) on extinguishment of debt	49		26		60
Total revenues	2,435		(1,557)		894
Expenses:
Losses and loss adjustment	50
Total expenses	837		682		989
Income (loss) before income taxes	1,598		(2,239)		(95)
Provision (benefit) for income taxes	364		(920)		(148)
Net income (loss)	1,234		(1,319)		53
Net income (loss) per common share:
Basic	$ 6.36		$ (6.69)		$ 0.26
Diluted	$ 6.33		$ (6.69)		$ 0.26
Weighted average number of common shares outstanding:
Basic	193,842,435	[1]	197,019,968	[1]	202,421,433	[1]
Diluted	194,904,830		197,019,968		203,021,134
Non Variable Interest Entities [Member]
Premiums earned:
Scheduled premiums earned	372		456		504
Refunding premiums earned	233		149		90
Premiums earned (net of ceded premiums of $14, $12 and $28)	605		605		594
Net investment income	214		383		457
Fees and reimbursements	61		50		160
Change in fair value of insured derivatives:
Realized gains (losses) and other settlements on insured derivatives	(406)		(2,371)		(162)
Unrealized gains (losses) on insured derivatives	1,870		(441)		(607)
Net change in fair value of insured derivatives	1,464		(2,812)		(769)
Net gains (losses) on financial instruments at fair value and foreign exchange	55		(99)		88
Investment losses related to other-than-temporary impairments:
Investment losses related to other-than-temporary impairments	(58)		(125)		(206)
Other-than-temporary impairments recognized in accumulated other comprehensive income (loss)	(47)		24		142
Net investment losses related to other-than-temporary impairments	(105)		(101)		(64)
Net gains (losses) on extinguishment of debt			26		35
Other net realized gains (losses)	7		(1)		29
Expenses:
Losses and loss adjustment	50		(80)		232
Amortization of deferred acquisition costs	50		63		59
Operating	381		308		290
Interest	284		300		325
Variable Interest Entity [Member]
Premiums earned:
Net investment income	67		70		73
Change in fair value of insured derivatives:
Net gains (losses) on financial instruments at fair value and foreign exchange	18		59		342
Investment losses related to other-than-temporary impairments:
Net gains (losses) on extinguishment of debt	49				25
Other net realized gains (losses)			263		(76)
Expenses:
Operating	17		29		24
Interest	$ 55		$ 62		$ 59

[1] Includes 5,514,523, 5,080,742 and 5,325,428 of unvested restricted stock and units that receive nonforfeitable dividends or dividend equivalents for the years ended December 31, 2012, 2011 and 2010, respectively.