Expected Loss to be Paid - Narrative Net Expected Recoveries from Breaches of R&W (Details) - RMBS - U.S. - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Schedule of Expected Losses to be Paid [Line Items]
Future net R&W benefit	$ 82	$ 53
Second Lien
Schedule of Expected Losses to be Paid [Line Items]
Period from plateau to intermediate conditional default rate (in months)	28 months
Second Lien | Most Stressful
Schedule of Expected Losses to be Paid [Line Items]
Period from plateau to intermediate conditional default rate (in months)	31 months