Consolidated Statements Of Operations - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Change in fair value of insured derivatives:
Unrealized gains (losses) on insured derivatives			$ 32	$ (16)
Net change in fair value of insured derivatives	$ (7)	$ 3	(12)	(50)
Net gains (losses) on financial instruments at fair value and foreign exchange	22	(61)	13	(44)
Net investment losses related to other-than-temporary impairments:
Net investment losses related to other-than-temporary impairments	(1)	(11)	(2)	(13)
Net gains (losses) on extinguishment of debt	0	0	0	8
Other net realized gains (losses)	0	34	(1)	37
Total revenues	12	72	85	149
Expenses:
Losses and loss adjustment	59	170	131	264
Interest	52	50	103	98
Total expenses	158	282	327	479
Income (loss) before income taxes	(146)	(210)	(242)	(330)
Provision (benefit) for income taxes	0	1,019	2	971
Net income (loss)	$ (146)	$ (1,229)	$ (244)	$ (1,301)
Net income (loss) per common share:
Basic	$ (1.64)	$ (9.78)	$ (2.75)	$ (10.13)
Diluted	$ (1.64)	$ (9.78)	$ (2.75)	$ (10.13)
Weighted average number of common shares outstanding:
Basic	89,131,760	125,653,189	88,865,272	128,511,897
Diluted	89,131,760	125,653,189	88,865,272	128,511,897
Non Variable Interest Entity [Member]
Premiums earned:
Scheduled premiums earned	$ 29	$ 28	$ 52	$ 56
Refunding premiums earned	7	16	24	37
Premiums earned (net of ceded premiums of $1, $1, $3 and $3)	36	44	76	93
Net investment income	34	37	65	89
Fees and reimbursements	0	6	6	8
Change in fair value of insured derivatives:
Realized gains (losses) and other settlements on insured derivatives	(25)	(3)	(44)	(34)
Unrealized gains (losses) on insured derivatives	18	6	32	(16)
Net change in fair value of insured derivatives	(7)	3	(12)	(50)
Net gains (losses) on financial instruments at fair value and foreign exchange	22	(61)	13	(44)
Net investment losses related to other-than-temporary impairments:
Investment losses related to other-than-temporary impairments	0	(54)	0	(54)
Other-than-temporary impairments recognized in accumulated other comprehensive income (loss)	(1)	43	(2)	41
Net investment losses related to other-than-temporary impairments	(1)	(11)	(2)	(13)
Net gains (losses) on extinguishment of debt	0	0	0	8
Other net realized gains (losses)	0	34	(1)	37
Expenses:
Losses and loss adjustment	59	170	131	264
Amortization of deferred acquisition costs	4	8	8	15
Operating	19	32	39	61
Interest	52	50	103	98
Variable Interest Entity Primary Beneficiary [Member]
Premiums earned:
Net investment income	8	6	16	12
Change in fair value of insured derivatives:
Net gains (losses) on financial instruments at fair value and foreign exchange	13	14	17	(19)
Net investment losses related to other-than-temporary impairments:
Other net realized gains (losses)	(93)	0	(93)	28
Expenses:
Operating	3	3	5	5
Interest	$ 21	$ 19	$ 41	$ 36