Expected Loss to be Paid - Net Expected Loss to be Paid (Recovered) and Net Economic Loss Development (Benefit) by Accounting Model (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	$ 737	$ 1,183	$ 1,303
Net Economic Loss Development (Benefit)	(1)	(5)
Financial Guarantee Accounted for as Insurance Contracts [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	683	1,110
Net Economic Loss Development (Benefit)	14	(9)
Financial Guarantee Variable Interest Entities And Other [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	58	75
Net Economic Loss Development (Benefit)	(29)	(13)
Financial Guarantee Accounted for as Credit Derivatives [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	(4)	(2)
Net Economic Loss Development (Benefit)	14	17
United States [Member] | Residential Mortgage-Backed Securities (RMBS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	146	293	$ 73
Net Economic Loss Development (Benefit)	(234)	(69)
First Lien [Member] | United States [Member] | Residential Mortgage-Backed Securities (RMBS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	166	243
Net Economic Loss Development (Benefit)	(77)	16
Second Lien [Member] | United States [Member] | Residential Mortgage-Backed Securities (RMBS) [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	20	50
Net Economic Loss Development (Benefit)	$ (157)	$ (85)