Consolidated Statements Of Operations (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Change in fair value of insured derivatives:
Unrealized gains (losses) on insured derivatives					$ 1,562		$ 1,473
Net change in fair value of insured derivatives	257		(21)		14		1,053
Net gains (losses) on financial instruments at fair value and foreign exchange	5		7		62		(18)
Investment losses related to other-than-temporary impairments:
Net investment losses related to other-than-temporary impairments	0		(8)		0		(105)
Net gains (losses) on extinguishment of debt	6		0		49		0
Other net realized gains (losses)	(29)		1		(29)		7
Total revenues	420		281		751		1,703
Expenses:
Losses and loss adjustment	98		171		92		330
Interest	59		69		179		214
Total expenses	249		338		629		944
Income (loss) before income taxes	171		(57)		122		759
Provision (benefit) for income taxes	39		(64)		4		161
Net income (loss)	132		7		118		598
Net income (loss) per common share:
Basic	$ 0.68		$ 0.04		$ 0.61		$ 3.09
Diluted	$ 0.67		$ 0.04		$ 0.60		$ 3.07
Weighted average number of common shares outstanding:
Basic	192,711,608	[1]	193,879,994	[1]	193,440,078	[1]	193,760,654	[1]
Diluted	196,746,771		194,977,642		197,762,488		194,835,537
Non Variable Interest Entity [Member]
Premiums earned:
Scheduled premiums earned	80		85		236		291
Refunding premiums earned	24		70		112		173
Premiums earned (net of ceded premiumsof $2, $3, $7 and $12)	104		155		348		464
Net investment income	42		50		118		172
Fees and reimbursements	5		20		17		47
Change in fair value of insured derivatives:
Realized gains (losses) and other settlements on insured derivatives	(28)		12		(1,548)		(420)
Unrealized gains (losses) on insured derivatives	285		(33)		1,562		1,473
Net change in fair value of insured derivatives	257		(21)		14		1,053
Net gains (losses) on financial instruments at fair value and foreign exchange	5		7		62		(18)
Investment losses related to other-than-temporary impairments:
Investment losses related to other-than-temporary impairments	0		(3)		0		(58)
Other-than-temporary impairments recognized in accumulated other comprehensive income (loss)	0		(5)		0		(47)
Net investment losses related to other-than-temporary impairments	0		(8)		0		(105)
Net gains (losses) on extinguishment of debt	6		0		49		0
Other net realized gains (losses)	(29)		1		(29)		7
Expenses:
Losses and loss adjustment	98		171		92		330
Amortization of deferred acquisition costs	9		8		36		36
Operating	71		72		280		307
Interest	59		69		179		214
Variable Interest Entity Primary Beneficiary [Member]
Premiums earned:
Net investment income	13		17		43		51
Change in fair value of insured derivatives:
Net gains (losses) on financial instruments at fair value and foreign exchange	17		44		128		(17)
Investment losses related to other-than-temporary impairments:
Net gains (losses) on extinguishment of debt	0		16		0		49
Other net realized gains (losses)	0		0		1		0
Expenses:
Operating	2		5		8		14
Interest	$ 10		$ 13		$ 34		$ 43

[1] Includes 4,349,481 and 5,524,396 of unvested restricted stock and units that receive nonforfeitable dividends or dividend equivalents for the three months ended September 30, 2013 and 2012,respectively. Includes 4,981,970 and 5,442,143 of unvested restricted stock and units that receive nonforfeitable dividends or dividend equivalents for the nine months endedSeptember 30, 2013 and 2012, respectively.