Segment Information - Reconciliation of Total GAAP Revenues to Segment Revenues and Expenses (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Total GAAP revenues	$ 372	$ 266	$ 468	$ 461
Less: Realized gains (losses) on investments	4	8	(1)	(4)
Less: Non-credit impairment unrealized fair value gains (losses) on credit derivatives	100	12	23	(9)
Less: Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves			55	3
Plus: Credit derivative losses	1	21	3	25
Segment Revenue, Including Adjustments	294	263	484	497
Benefits, Losses and Expenses	150	85	304	224
Total expenses	150	85	296	223
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total GAAP revenues	372	266	468	461
Benefits, Losses and Expenses	150	85	304	224
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Less: Realized gains (losses) on investments	4	8	(1)	(4)
Less: Non-credit impairment unrealized fair value gains (losses) on credit derivatives	97	(12)	9	(40)
Fair value gains (losses) on FG VIEs	(25)	19	23	10
Less: Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	2	(12)	(55)	(3)
Plus: Credit derivative losses	0	0	(8)	(1)
Segment Revenue, Including Adjustments	35	21	16	21
Total expenses	$ 4	$ 14	$ 3	$ 14