Expected Loss to be Paid Expected Loss to be Paid - Net Economic Loss Development (Benefit) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Expected Losses to be Paid [Line Items]
Economic loss development after recoveries for R&W	$ 70	$ 25	$ 101	$ (14)
RMBS | U.S.
Schedule of Expected Losses to be Paid [Line Items]
Economic loss development after recoveries for R&W	1	(40)	(61)	(223)
RMBS | U.S. | First Lien
Schedule of Expected Losses to be Paid [Line Items]
Economic loss development after recoveries for R&W	(6)	27	49	77
RMBS | U.S. | Second Lien
Schedule of Expected Losses to be Paid [Line Items]
Economic loss development after recoveries for R&W	$ 5	$ 13	$ 12	$ 146