Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Statement of Cash Flows [Abstract]
Proceeds From Issuance of Ambac UK Debt	$ 0	$ 12
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	34	46
Cash flows from operating activities:
Net income attributable to common shareholders	(315)	(172)
Net income (loss)	(315)	(172)
Adjustments to reconcile net income to net cash used in operating activities:
Amortization of bond premium and discount	(8)	(55)
Share-based compensation	6	7
Deferred income taxes	(8)	(1)
Current income taxes	(7)	33
Unearned premiums, net	(19)	(68)
Losses and loss expenses, net	71	(388)
Ceded premiums payable	(2)	(2)
Premium receivables	24	54
Accrued interest payable	46	42
Amortization of insurance intangible assets	27	263
Net mark-to-market (gains) losses	1	(1)
Net realized investment gains	(18)	(53)
Variable interest entity activities	(3)	(19)
Increase (Decrease) in Derivative Assets and Liabilities	21	(1)
Other, net	72	95
Net cash used in operating activities	(112)	(265)
Cash flows from investing activities:
Proceeds from sales of bonds	876	689
Proceeds from matured bonds	75	274
Purchases of bonds	(685)	(427)
Proceeds from sales of other invested assets	361	48
Purchases of other invested assets	(401)	(117)
Change in short-term investments	(38)	(342)
Change in cash collateral receivable	(13)	65
Proceeds From Financial Guaranty Variable Interest Entity Assets	98	122
Other, net	(2)	0
Net cash provided by (used in) investing activities	270	313
Cash flows from financing activities:
Paydown of Ambac Note	(103)	(22)
Paydown of Financial Guaranty Variable Interest Entity Liabilities	(99)	(92)
AMPS Proceeds	0	19
Payment, Tax Withholding, Share-based Payment Arrangement	(3)	(2)
Net cash used in financing activities	(205)	(85)
Effect of Exchange Rate on Cash and Cash Equivalents	0	0
Net cash flow	(47)	(37)
Cash, cash equivalents, and restricted cash at end of period	$ 17	$ 18