Segment Information - Reconciliation of Total GAAP Revenues to Segment Revenues and Expenses (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting Information [Line Items]
Total GAAP revenues	$ 96	$ 195
Less: Realized gains (losses) on investments	5	12
Less: Non-credit impairment unrealized fair value gains (losses) on credit derivatives	(77)	(21)
Less: Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	(58)	9
Plus: Credit derivative losses	2	4
Benefits, Losses and Expenses	154	139
Total expenses	146	138
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total GAAP revenues	96	195
Benefits, Losses and Expenses	154	139
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Less: Realized gains (losses) on investments	5	12
Less: Non-credit impairment unrealized fair value gains (losses) on credit derivatives	(88)	(28)
Less: Fair value gains (losses) on CCS	(48)	9
Less: Foreign exchange gains (losses) on remeasurement of premiums receivable and loss and LAE reserves	(57)	9
Plus: Credit derivative losses	(8)	(1)
Total expenses	$ (1)	$ 0