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, 2018	Dec. 31, 2017	Dec. 31, 2016
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	$ 1,183	$ 1,303	$ 1,198
Net Economic Loss Development (Benefit)	(5)	313
Financial Guarantee Accounted for as Insurance Contracts [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	1,109	1,226
Net Economic Loss Development (Benefit)	(9)	353
Financial Guarantee Variable Interest Entities And Other [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	76	91
Net Economic Loss Development (Benefit)	(13)	(6)
Financial Guarantee Accounted for as Credit Derivatives [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	(2)	(14)
Net Economic Loss Development (Benefit)	17	(34)
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)	293	73	$ 206
Net Economic Loss Development (Benefit)	(69)	(181)
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)	243	123
Net Economic Loss Development (Benefit)	16	1
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)	50	50
Net Economic Loss Development (Benefit)	$ (85)	$ (182)