Segment Information - Reconciliation of Total GAAP Revenues to Segment Revenues and Expenses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting Information [Line Items]
Total consolidated revenues	$ 268	$ 206	$ 736	$ 667
Realized gains (losses) on investments	13	16	12	12
Less: Non-credit impairment unrealized fair value gains (losses) on credit derivatives	2	8	25	(1)
Less: Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves			14	24
Plus: Credit derivative impairment (recoveries)	6	5	9	30
Total segment revenues	232	223	716	720
Total consolidated expenses	196	120	500	344
Total expenses	200	130	496	353
Operating Segments
Segment Reporting Information [Line Items]
Total consolidated revenues	268	206	736	667
Total consolidated expenses	196	120	500	344
Other
Segment Reporting Information [Line Items]
Realized gains (losses) on investments	13	16	12	12
Less: Non-credit impairment unrealized fair value gains (losses) on credit derivatives	(3)	11	6	(29)
Fair value gains (losses) on FG VIEs	(10)	(14)	13	(4)
Less: Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	40	(20)	(15)	(23)
Plus: Credit derivative impairment (recoveries)	4	10	(4)	9
Total segment revenues	17	0	33	21
Total expenses	$ 5	$ 2	$ 8	$ 16