Consolidated Statements Of Operations - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Premiums earned:
Premiums earned (net of ceded premiums of $6, $7 and $9)		$ 201	$ 300	$ 372
Change in fair value of insured derivatives:
Unrealized gains (losses) on insured derivatives		0	21	157
Net change in fair value of insured derivatives		(51)	(19)	129
Net gains (losses) on financial instruments at fair value and foreign exchange		(24)	84	63
Net investment losses related to other-than-temporary impairments:
Net investment losses related to other-than-temporary impairments		(106)	(5)	(13)
Net gains (losses) on extinguishment of debt		28	5	(1)
Other net realized gains (losses)		31	(282)	17
Total revenues		433	294	853
Expenses:
Losses and loss adjustment		683	220	123
Interest		197	197	199
Total expenses		1,094	633	564
Income (loss) before income taxes		(661)	(339)	289
Provision (benefit) for income taxes		944	(1)	109
Net income (loss)		$ (1,605)	$ (338)	$ 180
Net income (loss) per common share:
Basic		$ (13.5)	$ (2.54)	$ 1.06
Diluted		$ (13.5)	$ (2.54)	$ 1.06
Weighted average number of common shares outstanding:
Basic	[1]	118,930,282	133,001,088	163,936,318
Diluted		118,930,282	133,001,088	164,869,788
Non Variable Interest Entity [Member]
Premiums earned:
Scheduled premiums earned		$ 107	$ 168	$ 199
Refunding premiums earned		94	132	173
Premiums earned (net of ceded premiums of $6, $7 and $9)		201	300	372
Net investment income		154	152	152
Fees and reimbursements		15	28	6
Change in fair value of insured derivatives:
Realized gains (losses) and other settlements on insured derivatives		(51)	(40)	(28)
Unrealized gains (losses) on insured derivatives		0	21	157
Net change in fair value of insured derivatives		(51)	(19)	129
Net gains (losses) on financial instruments at fair value and foreign exchange		(24)	84	63
Net investment losses related to other-than-temporary impairments:
Investment losses related to other-than-temporary impairments		(101)	(1)	(12)
Other-than-temporary impairments recognized in accumulated other comprehensive income (loss)		(5)	(4)	(1)
Net investment losses related to other-than-temporary impairments		(106)	(5)	(13)
Net gains (losses) on extinguishment of debt		28	5	(1)
Other net realized gains (losses)		31	(282)	17
Expenses:
Losses and loss adjustment		683	220	123
Amortization of deferred acquisition costs		23	40	50
Operating		106	137	140
Interest		197	197	199
Variable Interest Entity Primary Beneficiary [Member]
Premiums earned:
Net investment income		27	31	86
Change in fair value of insured derivatives:
Net gains (losses) on financial instruments at fair value and foreign exchange		130	0	42
Net investment losses related to other-than-temporary impairments:
Other net realized gains (losses)		28	0	0
Expenses:
Operating		10	14	13
Interest		$ 75	$ 25	$ 39

[1] Includes 0.3 million, 0.9 million and 0.6 million of participating securities that met the service condition and were eligible to receive nonforfeitable dividends or dividend equivalents for the years ended December 31, 2017, 2016 and 2015, respectively.