Contracts Accounted for as Insurance - Gross Premium Receivable Net of Commissions on Assumed Business Roll Forward (Details) - USD ($) $ in Millions		12 Months Ended
	Jun. 01, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Gross Premium Receivable Net of Ceding Commissions [Roll Forward]
Beginning of period		$ 904	$ 915	$ 576
Less: Specialty insurance premium receivable		2	1	1	$ 0
Financial guaranty insurance premiums receivable		1,284	903	914	$ 576
Premiums receivable from acquisitions (see Note 2)		0	0	270
Gross written premiums on new business, net of commissions (1)		689	610	301
Gross premiums received, net of commissions		(318)	(577)	(301)
Adjustments:
Changes in the expected term		(21)	(8)	(8)
Accretion of discount, net of commissions on assumed business		10	9	12
Foreign exchange translation and remeasurement		21	(35)	64
Cancellation of assumed reinsurance		0	(10)	0
End of period		1,286	904	915
Variable Interest Entity, Primary Beneficiary [Member]
Gross Premium Receivable Net of Ceding Commissions [Roll Forward]
Beginning of period		9	10
Adjustments:
End of period		7	9	10
Reinsurance of SGI Insured Portfolio [Member]
Gross Premium Receivable Net of Ceding Commissions [Roll Forward]
Gross written premiums on new business, net of commissions (1)	$ 330
Foreign Currency Gain (Loss) [Member]
Adjustments:
Foreign exchange translation and remeasurement		$ 21	$ (33)	$ 61