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, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Gross Premium Receivable Net of Ceding Commissions [Roll Forward]
Beginning of period		$ 915	$ 576	$ 693
Less: Non-financial guaranty insurance premium receivable		1	1	0	$ 0
FG insurance premiums receivable		903	914	576	$ 693
Premiums receivable from acquisitions (see Note 2)		0	270	18
Gross written premiums on new business, net of commissions (1)		610	301	193
Gross premiums received, net of commissions (2)		(577)	(301)	(258)
Adjustments:
Changes in the expected term		(8)	(8)	(38)
Accretion of discount, net of commissions on assumed business		9	12	9
Foreign exchange translation and remeasurement (3)		(35)	64	(41)
Cancellation of assumed reinsurance		(10)	0	0
End of period		904	915	576
Variable Interest Entity, Primary Beneficiary [Member]
Gross Premium Receivable Net of Ceding Commissions [Roll Forward]
Beginning of period		10	11
Adjustments:
End of period		9	10	11
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
Gross premiums received, net of commissions (2)	$ (275)
Foreign Currency Gain (Loss) [Member]
Adjustments:
Foreign exchange translation and remeasurement (3)		$ (33)	$ 61	$ (36)